A method and system for use in regulating the circadian rhythm

Abstract

A computer implemented system for regulating the circadian rhythm of a human subject including a display device 150 configured to access a set of images, each image corresponding to a solar elevation

Description

Field The present application relates to a method and system for use in regulating the circadian rhythm of a human subject. Background A solar day may be defined as the period taken for the sun to return to the same azimuthal position in the sky. For example, in the northern hemisphere the duration of a day may be taken as the period between two successive positionings of the sun due south at noon. This period as measured in astronomical terms is not entirely constant, but rather varies through the year because of the elliptical orbital motion of the earth around the sun. To avoid such complexity, a consistent 24 hour solar clock has been defined for use in civilian life based on mean solar time. An Equation of Time is used to specify the offset between mean solar time and apparent solar time (also referred to as astronomical time, as would be measured using a sun-dial). In practice, this offset is relatively small, typically varying by approximately up to ±15 minutes through the year. It is readily apparent that the daily solar cycle has a very significant impact on the natural world. For example, flowers may open during daylight hours but close again overnight, while some animals are nocturnal, active during the night but sleeping during the day. Humans also experience the daily solar cycle, typically being awake and active during the day and sleeping at night. During the twentieth century it became widely understood that the daily solar cycle and the routine associated with it affect behavioural and metabolic aspects of humans which may become synchronised with external (environmental) influences. Strictly speaking, some influences might be aligned with apparent solar time (such as the decline in daylight as the evening progresses), while other influences might be aligned with mean solar time (such as catching a particular train or bus each day for commuting to work). However, as noted above, the offset between apparent and mean solar time is relatively small, so we consider their influence herein as both acting together within the general ambit of a solar cycle. The aspects of human behaviour and metabolism that are sensitive to the solar day are referred to as the circadian rhythm (or sometimes as the circadian cycle), where “circadian” is derived from the Latin meaning “about a day”. Note that the terms circadian rhythm and circadian cycle are generally used synonymously (interchangeably) within the present application. A circadian cycle or rhythm may also sometimes be referred to informally as a body clock. Further background information about circadian rhythms can be found at https: / / en.wikipedia.org / wiki / Circadian_rhythm and in many other documents. It is known that various aspects of the circadian rhythm may be generally maintained even for people who are deprived of feedback from external influences that would normally play a role in setting the pace of the circadian rhythm. For example, a human subject may (usually for experimental reasons) inhabit a cave or underground structure without access to natural light or other indicators of the solar day. In such circumstances, the circadian rhythm of the human subject may initially stay aligned with the solar day, even without receiving external feedback confirming such alignment. However, in the absence of external feedback for a longer duration, the circadian rhythm of such a person may drift out of alignment with the solar day. We can approximate a circadian cycle (C) as a function of time (t) by the formula: C = A sin (2TTt / P + (p) where A is the amplitude, P is the period of the circadian cycle and <p is the phase of the circadian cycle. In practice, it is relatively unusual for humans to experience an environment which completely lacks external influences - usually there is some form connection or grounding to the normal 24 hour cycle. However, for certain people the period P of the circadian cycle may potentially drift away from the normal 24 hour hours, for example, a patient in intensive care or otherwise suffering from significant medical issues. A more common concern for maintaining body clocks is where the period of the circadian rhythm may be generally maintained at 24 hours, corresponding to the solar day, but the phase q> of the circadian rhythm is shifted (offset) in an abrupt manner. Such a situation may arise, for example, after an intercontinental flight which involves a large time difference. In this case, the phase of the circadian rhythm of a traveller is initially aligned with their starting location, but is offset from the phase of the solar day in their new location, as indicated by external factors such as daylight hours, meal times, and so on. For example, a flight from London to New York typically takes 8 hours, but the time difference between London and New York (in terms of the local solar time) is only 5 hours. Accordingly, there is a mismatch (phase offset) between (i) the circadian cycle of a traveller aligned with their starting location and (ii) the external factors at the destination, with the former 3 hours ahead of the latter. This phase offset between the circadian rhythm and the external influences may give rise to jet lag involving negative metabolic and / or physiological conditions, such as potential problems with insomnia, digestion, and so on. An analogous phase offset may occur when a worker has their shift changed from night-time to day-time (or vice versa). Again, this abrupt transition may result in a phase offset between the circadian rhythm from the original night-time shift and the external factors now being experienced according to the new day-time shift. As above, such a phase offset may give rise to metabolic and / or physiological problems. In some cases, such problems may also arise simply from working a night-shift, in that the worker may receive conflicting external feedback. For example, a user might be active during the night performing shift work, but then experience increasingly bright daylight while travelling home. Such daylight would normally be indicative for a human of the start of the day, rather than a time to go to sleep. Hospital patients are also susceptible to problems with the phase shifts of their circadian rhythm. For example, a hospital patient who has undergone a surgical procedure may be unconscious (anaesthetised) during the day, and then wake up during the night feeling alert and unable to sleep further. The resulting phase mismatch between the circadian rhythm and external environmental influences may again cause metabolic and / or physiological problems. Similarly, a patient may suffer from pain or discomfort at night, so that they are unable to sleep during this period, contrary to their normal circadian cycle. An additional problem in a medical context is that different aspects of the circadian rhythm may go out of synchronisation with one another in an individual. For example, a patient may be given drugs that suppress a first aspect of metabolism but not a second aspect of metabolism. It is also possible in a medical context that an injury or disease may directly disrupt a metabolic or physiological aspect of the circadian rhythm, which again may cause a lack of synchronisation between different aspects of the circadian rhythm and have therefore have a negative health impact on a patient. Summary A system and method are provided for use in regulating and / or restoring the circadian rhythm of a human subject as disclosed herein. The ability to help maintain and / or restore such a circadian rhythm offers various benefits for human health as described in more detail herein. The system includes a display device and may be configured to access a set of images, each image corresponding to a solar elevation and providing a view indicative of the corresponding solar elevation. The system may be further configured to display on the display device to a human subject a sequence of images from the set of images to provide a sequence of views indicative of a change in solar elevation with time. The method may similarly access a set of images, each image corresponding to a solar elevation and providing a view indicative of the corresponding solar elevation. The method may further display on the display device to a human subject a sequence of images from the set of images to provide a sequence of views indicative of a change in solar elevation with time. Brief Description of the Figures Various implementations of the claimed invention will now be described by way of example only with reference to the following drawings. Figure 1 is a schematic diagram of one example of a system for helping to regulate circadian rhythm as disclosed herein. Figure 1A is a schematic diagram showing a wider variety of metabolic and physiological processes that are affected by the circadian cycle. (This figure is taken from https: / / en.wikipedia.org / wiki / Circadian_rhythm). Figure 2 is a schematic diagram of one example of the system of Figure 1 being installed for use by a patient in a bed. Figure 3 is a photograph showing a trial installation of an example implementation of the system of Figures 1 and / or 2. Figure 4 is a schematic diagram of another example of a system for helping to regulate circadian rhythm as disclosed herein. Figure 5 is a flowchart illustrating an example of using a system such as shown in Figure 1 to help regulate the circadian rhythm as described herein. Detailed Description In 1991 Russell G. Foster and colleagues including Ignacio Provencio discovered a non-rod, non-cone photoreceptor in the eyes of mice where it was shown to mediate circadian rhythms, i.e. the body's 24-hour biological clock [1], These cells express the photopigment melanopsin which was first identified by Provencio and colleagues [2], Compared to the rods and cones in the human eye, the intrinsically photosensitive retinal ganglion cells (ipRGC) and represent just a small subset (~1-3%) of the retinal ganglion cells. The ipRGC are sluggish and signal the presence of light over the long term. Their functional roles are non-image-forming and fundamentally different from those of pattern vision - rather they provide a stable representation of ambient light intensity. The ipRGC have at least three primary functions: i) they play a major role in synchronizing circadian rhythms to the 24-hour light / dark cycle, providing primarily length-of-day and length-of night information. They send light information via the retinohypothalamic tract directly to the circadian pacemaker of the brain, the suprachiasmatic nucleus of the hypothalamus. The physiological properties of these ganglion cells match known properties of the daily light entrainment (synchronization) mechanism regulating circadian rhythms. ii) photosensitive ganglion cells innervate other brain targets, such as the center of pupillary control, the olivary pretectal nucleus of the midbrain. They contribute to the regulation of pupil size and other behavioral responses to ambient lighting conditions. iii) they contribute to photic regulation of, and acute photic suppression of, release of the hormone melatonin from the pineal gland. Photosensitive ganglion cells are also responsible for the persistence of circadian and pupillary light responses in mammals with degenerated rod and cone photoreceptors, such as humans suffering from retinitis pigmentosa. Recently photoreceptive ganglion cells have been isolated in humans where, in addition to the above functions shown in other mammals, they have been shown to mediate a degree of light recognition in rodless, coneless subjects suffering with disorders of rod and cone photoreceptors. Work by Farhan H. Zaidi and colleagues has showed that photoreceptive ganglion cells may have a visual function and can be isolated in humans [3], The photopigment of photoreceptive ganglion cells, melanopsin, is excited by light mainly in the blue portion of the visible spectrum (the absorption peaks at ~480 nanometers). The phototransduction mechanism in these cells is not fully understood, but seems likely to resemble that in invertebrate rhabdomeric photoreceptors. Photosensitive ganglion cells respond to light by depolarizing and increasing the rate at which they fire nerve impulses. In addition to responding directly to light, these cells may receive excitatory and inhibitory influences from rods and cones by way of synaptic connections in the retina. Having an out of synchronisation circadian body clock is through to be associated with the instigation of heart disease, cancers, an diabetes to name but a few. Figure 1 is a schematic diagram of one example of a system 10 for helping to regulate circadian rhythm as disclosed herein. The two main components of the system 10 are a computing device 100 and display devices 150a, 150b, collectively referred to herein as display device(s) 150. The number of display devices 150 in the system 10 may vary from one implementation to another. For example, some implementations may comprise a single display device 150 while other implementations may have multiple (two or more) display devices 150a, 150b. Such display devices may also be referred to as monitors. The system 10 is intended for installation and use in buildings used to provide medical services, such as a hospital or nursing home. In a typical configuration, a patient will lie on a bed and the display devices will be located above the patient, hence the patient will look upwards from the bed and see the display device(s) 150. The computing device 100 is configured to provide an image or images as described below which may be used to help regulate the circadian cycle of the patient. In effect, the display device(s) 150 act as an external influencer or indicator of the phase of the circadian cycle, such that in response to viewing the image(s) on the display device, the circadian rhythm of the patient will tend to synchronise or align with the circadian cycle as depicted on the display device. In some cases, the main purpose of the system 10 may be to align the circadian cycle of the patient to an appropriate phase. For example, as described above, the circadian rhythm of a patient who has undergone surgery or some other significant treatment (or illness) may no longer be synchronised to their external environment - e.g. the body clock of the patient may indicate that it is nighttime (so that certain metabolic function may, for example, be naturally suppressed), whereas the actual (solar) time external to the building may be midday. As described in more detail below, the system 10 may use the computing device 100 and the display device(s) 150 to gradually change the phase of the circadian cycle for the patient so that the body clock of the patient is brought back into alignment with the solar cycle. Achieving this alignment may facilitate discharge of the patient, whereby when he / she leaves the building, the patient does not experience or suffer from any mismatch between (i) their own body clock and (ii) external factors such as daylight and normal personal and domestic routines. Figure 1A is a schematic diagram showing some of the biological elements of the circadian circle. (This figure is taken from https: / / en.wikipedia.org / wiki / Circadian_rhythm). As described herein, the computer 100 may be configured to display day time scenes in unison with the daily and seasonally cycles. The system 10 may therefore be utilised as a “circadian rhythm regulating” system which may be used to restore the body clock of a patient back into synchronism with the natural daily cycle. In other words, the control program of system 10 (such as running on computer 100) has the ability to adjust the operation of system 10 so as to resynchronise the circadian body clocks - this in turn reduces the effects and likelihood of circadian clocks for organs going out of synchronisation with one another. In addition, the circadian rhythm regulating program may contribute to brain function resetting. System 10 may also help in a situation in which there is some internal inconsistency in the circadian cycle of a patient. For example, there may be a metabolic function which is out of phase with a physiological aspect, potentially because of illness, injury, or as a result of a treatment. The system 10 uses images on the display device(s) 150 to provide a clear and powerful representation of the circadian cycle. This representation provides external factors or indicators such that the various components of the internal circadian rhythm may be generally guided to synchronise (coalesce) with this externally visible cycle, so that all the various components of the circadian rhythm for the patient are brought into alignment with the phase of the circadian cycle as provided by system 10. There are different ways in which this alignment may be achieved. In some cases, the system 10 may display images representing a circadian cycle that is matched (aligned) to the solar time outside the building in which the patient is located. In this approach, the displayed images may be regarded external influencers that pull the patient circadian cycle into alignment with the circadian rhythm indicated by the images displayed by the system 10 on the display screen(s) 150. In other cases, the system 10 may display images representing a circadian cycle having a phase that is intermediate: (i) the solar time outside the building in which the patient is located, and (ii) the present circadian rhythm of the patient. The rationale here is that the circadian rhythm of the patient may be moved in multiple, gentler steps, each step representing a movement closer to the solar / civil time outside the building in which the patient is located, until ultimately the circadian rhythm of the patient is brought into alignment (conformity) with the solar time outside the building in which the patient is located. This latter approach may in some circumstances provide better (e.g. quicker or more reliable) alignment between the circadian rhythm of the patient and the solar time outside the building in which the patient is located. On the other hand, this latter approach may increase the complexity of operating the system 10, in that rather than having the system implement the same fixed solar cycle for all patients as per the former approach, the latter approach uses the system 10 to apply phase corrections which are different for different patients (according to the current state of their circadian rhythm for each patient). In addition, the phase corrections may potentially vary with time even for a single patient. As mentioned above, the display devices 150 are typically positioned such that they are visible to a patient lying on a bed looking upwards. If there are multiple display devices, they are generally configured to have a contiguous relationship, whereby the multiple display devices in effect emulate or give the impression of a single big screen. There are various potential reasons for system 10 having multiple display devices, such as display device 150A and display device 150B, rather than a single larger display device, equivalent to the screen size of both devices 150A, 150B. For example, in such a situation, devices 150A, 150B are smaller and lighter than a larger display and so are easier to transport and to fit. Moreover, with multiple devices 150, there may be some flexibility in arrangement. For example, if six devices 150 are available, these could be split into 3 arrays each of 2 devices (such as shown in Figure 1), or 2 arrays each of 3 devices, based for example, upon the current occupancy levels of beds in the hospital. Similarly, there may be more flexibility in the arrangement of multiple smaller display devices 150, since they may provide more options for fitting the display devices 150 onto ceilings of different sizes and / or shapes. The display devices 150 are located above the patient at a sufficient height to avoid any hindrance for personnel attending to the patient, along with any treatments and equipment they need to support the patient. In some cases, the display device(s) 150 may be fastened directly to the ceiling above the patient bed; in other cases, the display device(s) may be suspended from the ceiling, such that they are located a certain distance below the ceiling. Having the display devices suspended in this manner allows the display devices(s) to be somewhat closer to the patient and so to occupy more of the field of view of the patient, thereby providing stronger input relating to the circadian cycle. Another possibility is that suspending the display devices 150 potentially allows the same field of view of the patient to be provided by a physically smaller (and hence cheaper) display device. It will be appreciated that any suspended display device 150 will still be at a sufficient height above the bed to avoid any hindrance for other treatments and equipment provided for the patient and so on, as discussed above. A further possibility is that the display device(s) are supported by one or more walls adjacent to the patient, for example, using a cantilever arrangement. Although the display device(s) 150 in most installation are located in a substantially horizontal plane located above the patient, other geometries may be adopted according to the particular circumstances, such as the condition of the patient. For example, having the display device(s) located in a horizontal plane above the patient is generally suitable for a patient who is spending a lot of time lying horizontally on the bed. However, in some cases a patient may have more of a sitting posture, with their head above their legs, and the torso having an inclined or vertical orientation. In this latter configuration, it may be easier for the patient to view the display device(s) with more of a horizontal line of sight. Accordingly, the display device(s) may be located (at least in part) on a wall which faces the patient, so that the patient is looking at the display devices(s) along a substantially horizontal direction from their inclined or upright position. It will be appreciated that the mounting geometries and orientations discussed above are provided by way of example, but without limitation. Furthermore, while some display device(s) 150 may be installed into a generally fixed position, in other implementations, the mounting for the display device(s) might provide more flexibility to allow staff to reconfigure the positions of the display devices 150 as appropriate having regard to the current posture of the patient (such as lying on the bed flat on their back, or sitting upright in their bed). Furthermore, while in many implementations the display device(s) 150 may be fixed to the structure of the building (such as a wall or ceiling), in other cases the display device(s) may be at least partly supported by some other facility, such as a metal frame or scaffolding. Such a metal frame may be provided, for example, with wheels to allow easier movement of the display devices from one bed to another according to the particular conditions of the patients in the different beds. Again, it will be appreciated that such different types of mountings, fixed or movable, and so on, are provided by way of example, but without limitation. The computing device 100 is depicted in Figure 1 as including volatile storage 126, non-volatile storage 125, software 135, an input / output interface (IF) 120, processor 110 and positioning system 130. The computing device 100 may comprise a standard computing device such as a personal computer, a laptop, a notebook or notepad, a smartphone, etc. In some cases, the computing device 100 may comprised customised hardware or software for use in system 10, as described in more detail below. The computing device 100 includes one or more processors 110 which may be used for executing computer program instructions (software). The processor may be any suitable form of processor, for example as generally provided in conventional personal computers, laptops, tablet, notebooks, and so on. The processor(s) 110 may have multiple cores and may be implemented as an array of two or more individual processors. The one or more processors 110 may also comprise one or more graphics processing units (GPUs) which are generally adapted to provide high performance for image (graphics) processing. For example, a general purpose processor may off-load a computing task related to image processing onto one or more GPUs for greater processing efficiency. In many systems, the services of a GPU may be accessed via a graphics application programming interface (API), such as DirectX (from Microsoft) and OpenGL (https: / / opengl.org / ). The use of processor(s) 110 is generally well-known in the computing field, both with and without the inclusion of one or more GPUs. The volatile storage 126 in the computing device 100 is generally provided as random access memory (RAM) and is used to hold software instructions and data for use and execution by the processor(s) 110. This type of volatile storage is sometimes referred to as ‘memory’. The processor 110 itself generally includes a certain amount of RAM for holding software instructions and data in a cache to provide high speed access to these instructions and data. The use of such volatile storage (memory) 126 and a cache provided in conjunction with processor(s) 110 is generally well-known in the computing field. The non-volatile storage 125 in the computing device 100 is used to provide generally longer term storage compared to RAM 126. In particular, the contents of volatile memory 126 are wiped (lost) when the computing device 100 is powered down. In contrast, the non-volatile storage 125 maintains data across a power-off / power-on cycle. The nonvolatile storage 125 may be provided as solid state memory (such as ROM) and / or as hard disk storage. The non-volatile storage 125 is generally able to provide a large storage capacity - typically of the order of 1 Tbyte. This type of non-volatile storage is sometimes referred to as “storage”. The use of such non-volatile storage (storage) 125 is generally well-known in the computing field. As shown in Figure 1, the non-volatile storage 125 is used to hold software (computer programs, code, etc) 135 and data 136. This software can then be loaded onto the processor(s) 110 (typically via memory 126, but sometimes directly from storage 125) for execution. The software 135 generally comprises an operating system, such as Microsoft Windows or Google Android, and application programs which run on top of the operating system. The use of such software 135 is well-known in general terms in the computing field, but the software 135 may incorporate some functionality that is not generally known as described in more detail below. The data 136 in the non-volatile storage 125 may be loaded onto the processor(s) 110 (typically via memory 126, but sometimes directly from storage 125) to provide input for the computer software 135 which is running on the processor(s) 110. The data 136 may also comprise output from the computer software 135 running on the processor(s) which is written out to storage 125 (typically via memory 126). The use of data 136 to represent input to and output from the software 135 executing on processor(s) 110 is well-known in general terms in the computing field, but some of the data 136 is not generally known (especially in the context of the overall functionality of computing device 100 as described in more detail below). In system 10, the data 136 includes a time sequence of images. These images may be encoded as a video, such as in standard TV format, HDTV format, ultra HD, or any other suitable format. Alternatively, the data may comprise a succession (slide show) of images. The images are presented in sequence on the display device(s) 150. The use of a video format is more suited to images that have rapid movement or change. The images provided as data 136 generally do not have rapid movement or change; such images may typically be encoded more efficiently as a succession of still images rather than as an ongoing video. Figure 1 further depicts an input / output interface 120 for transmitting data from and receiving data to the computing device 100. In practice, interface 120 will typically include multiple different data connections which may be wired or wireless according to the nature and configuration of the connectors. Examples of such potential data connections include universal serial bus (USB) in various formats - micro, mini, Type C; (ROM) memory card slot; wireless links such as Bluetooth and / or Near Field Connections (NFC); local area network (LAN) connection - wired or wireless (WiFi); video graphics array (VGA) connector; and High Definition Multimedia Interface (HDMI). It will be appreciated that this list of examples is provided by way of illustration rather than limitation, and the skilled person is generally familiar not only with the above examples but also with other potential data connections for use with Input / Output interface 120. Figure 1 shows two data connections 105A, 105B, collectively referred to herein as data connections(s) 105. In particular, a data connection 105 is provided between the computing device 100 and each respective display device 150. Accordingly, the number of data connections 105 may vary to match the number of display devices 150 included in any particular implementation of system 10. In other implementations, multiple displace devices may potentially share a single cable 105 connected back to computing device 100. In the example, of Figure 1, data connectors 105,105B may be HDMI cables, but any other suitable form of data connection might be utilised instead. One advantage of using a physical (wired) connection between the computing device 100 and the display device(s) 150 is that some hospitals equipment may be sensitive to the use of wireless communications in the surrounding environment. In particular, there may be a risk of potential conflict or interference between wireless radio signals to be used by system 10 and existing (or future) medical apparatus which may use radio waves for data communications, remote control, position sensing, imaging, and so on, whereby such interference may (for example) introduce noise into medical imaging. Such interference or conflict may generally be avoided by the use of (shielded) physical cables 105 such as HDMI for connecting the display devices(s) 150 to the computing device 100. It will be appreciated that the display device(s) 150 are intended to allow a patient to view images relating to the circadian cycle which are presented on the display device(s) 150. In some cases, the computing device 100 may also be provided with a screen, keyboard, mouse, and / or touchscreen (not shown in Figure 1) that may be used by staff to interact with the system 10. For example, such staff may be nursing or other medical personnel, or engineering support personnel responsible for the system 10. Such interactions may be utilised to perform various operations to control, configure and adjust the system 10. For example, and without limitation, these additional forms of data communication (interaction, input-output) with system 10 may include positional configuration (as described below), starting and stopping the sequence of displayed images, selecting or adjusting the set of images to be displayed, adjusting the timing of the displayed images (such as the refresh rate), adjusting the brightness of the displayed images, and so on. Figure 1 further depicts a positioning system 130. The images to be displayed by system 10 on the display device(s) 150 depend on the local time and the latitude of the installed system 10. In some cases, the local (solar) time may be derived from the longitude and knowledge of universal time (UTC, coordinated universal time). There are various ways in which the positioning system 130 may acquire appropriate information to allow display of the suitable images on display device(s) 150. For example, the positioning system 130 may include a global positioning system (GPS) receiver which can be used to extract both time and position (longitude and latitude) for use in selecting the appropriate images from data 136 for display on devices 150. Although such a GPS receiver provides accurate information, it operates best outside, and may perform less well inside a building (such as in a hospital). Another option is that an operator or install engineer might just enter the position and local time directly into the positioning system 130. Such an operator or install engineer may first acquire an accurate position from a GPS receiver, cellphone (mobile phone) information, a hard copy map, and / or any other appropriate source. It will be appreciated that the GPS receiver may be used outside for this purpose because the difference in geographical location between being inside a hospital and outside the same hospital is too small to impact the regulation of circadian rhythms such as described herein. Likewise, the position information held by component 130 remains accurate (and so does not need to be updated) if the system 10 is moved around within the same building (e.g. hospital) or complex of buildings. Figure 2 is a schematic diagram of one example of the system 10 of Figure 1 being installed for use by a patient 230 in a bed 200. The bed 200 may typically be located in a hospital or other medical institution, but other locations are possible such as a care home or nursing home, or possibly a domestic property (house, etc) in which the resident is (largely) confined to bed. In Figure 2, the head of the bed 200 is positioned against a wall 220 which extends up to the ceiling 210. The space formed inter alia by wall 220 and ceiling 210 may, for example, be provided by a single room for the patient 230 or a by a portion of a shared space such as a hospital ward. In the latter case, the space associated with the patient 230 may be shielded by a curtain (not shown in Figure 2) that can be opened or closed. For example, opening the curtain may give the patient 230 more light and more space for visitors, while closing the curtain will generally give the patient more privacy. Figure 2 shows the display device 150 fastened to the ceiling 210 above the patient 230 and the computing device 100 fastened to the wall 220. As discussed in relation to Figure 1 above, the display device 150 may be represented by multiple monitors such as display devices 150A and 150B. A void (not shown in Figure 2) may be provided above the display device 150, for example to provide one or more of alternating current (AC) power supply, control commands, cooling, and so on. One way to provide such a void is to use a suspended ceiling, such as described below in conjunction with Figure 3. A typical installation may involve a minimum void clearance to be provided above at least part (e.g. >50%) of the display device, for example the void clearance may have a value in the range 0.2-0.8 m. The underside of the display device (i.e. the side facing the patient 230) may be provided with a non-reflective layer (not shown in Figure 2). This non-reflective layer may provide protection for patients who have sensitive eyes, such as some elderly patients who might otherwise be discomforted by reflections from the display device 150. (Such reflections may potentially occur when the display device is presenting an operational display and / or when the display device is not presenting an operational display). Furthermore, the system 10 including display device 150 is configured not to complete or conflict with other sources of light provided to the patient 230, such as ambient light, diagnostic light, reading light and so on. By way of example, a clinician may control the system 10 and display device 150 to fade or switch off any image presented on display device 150 during a diagnostic procedure to avoid such image causing an alteration in the perceived skin colour, thereby allowing the clinician to monitor the skin colour of the patient 230 on a more consistent and standardised basis. It will be appreciated that although the computing device 100 is shown in Figure 2 as being potentially located close to the head of the patient, the computing device will generally be located to the left or right of the bed 200 (when viewed from the foot of the bed). Amongst other things, such a sideways (left or right) location of the computing device allows an operator (e.g. a medical or engineering staff member, according to the operation to be performed) to access the computing device 100 without being hindered by the location of the patient 230. The system 10 (or some portion thereof, such as computing device 100) may link to or be incorporated into a bedhead trunking system which is used to provide a variety of facilities to the location of each bed 200, such as electrical networks, equipment sockets and connectors, medical gas supply, and so on (as appropriate). Further information about bedhead trunking can be found in “Specialist services: Health Technical Memorandum OS-OS: Bedhead services”, see: https: / / www.england.nhs.uk / wp-content / uploads / 2021 / 05 / HTM_08-03.pdf. Note that in some cases, a bedhead trunking facility may provide integral lighting. Such lighting may be detrimental to the operation of system 10 described herein, for example, because the integrated lighting may provide a glare that dilutes the circadian rhythm provided by system 10 and as experienced by patient 230. In such cases, various measures may be taken to reduce the glare, whether by controlling the bedhead trunking to provide a lower level of lighting (or no lighting at all), and / or to place an external cover on the bedhead trunking to reduce or remove any light or glare. The computing device 100 may be connected by cabling 105 to the display device 150 (for clarity, this cabling is omitted from Figure 2). In the configuration of Figure 2, the computing device 100 may be implemented as a tablet, notebook or similar, which can be retained substantially flush against wall 220. This positioning and implementation of the computing device 100 provides ready access for operating the computing device 100 but minimises interference with any other equipment which may be located for use with the patient 230, such as various medical devices. Other implementations however may be arranged to accommodate different forms of computing device 100, such as a laptop. In operation, the computing device arranges for a sequence of images (including potentially a video) to be displayed on the display device(s) 150. The positioning of the display device(s) 150 is such as to allow ready viewing of the display device(s) by the patient 230, such as indicated by arrow 240. As discussed in more detail below, the images are created to provide the patient 230 with external indicators of circadian rhythm. In this respect, it should be noted that the screen size of the display device 150 is relatively large to provide the patient 230 with a strong cue to the external environment (in contrast, a display device having a smaller screen size would provide a lower visual impact for the patient 230, and hence may be less effective in helping to regulate the circadian cycle). In some implementations, a facility may be provided for a patient 230 to have some (limited) control over the operation of the system 10. For example, the patient may be provided with a hand-held control unit (not shown in Figure 2) to turn the display device 150 off / on, and / or to control the brightness of the output from the display device. In some cases this control unit may be integrated into (or mounted on) a general nurse call facility for ease of operation, storage, and so on. Figure 3 is a photo showing a trial installation of an example implementation of the system 10. In particular, Figure 3 depicts part of a hospital ward including a wall with markings “3” and “4” which indicate respective bays for two beds located in the ward. Each bay is provided with a pair of adjacent display devices 150. The two display devices for a given bay are operated in conjunction with one another, in effect to show two display portions of a single image for each bay. In the example of Figure 3, each display device 150 has a size generally corresponding to the size of the tiles 211 forming a suspended ceiling 210. Each display device in effect therefore replaces a single ceiling tile 211 at that location. In this configuration, the display devices 150 are held in position by the general structure of the ceiling used to support the ceiling tiles; this can also be used to support the display devices which may replace certain ceiling tiles such as shown in Figure 3. It will be appreciated that the space above the ceiling tiles 211 is often used to provide cabling. Accordingly, the display devices 150 may be connected to receive power from the cabling that is already present above the ceiling tiles. Furthermore, the spacing above the ceiling tiles 211 might be used for routing connectors 105A, 105B between the display devices 150 and the computing device 100 (not shown in Figure 3) to allow images for display to be transmitted from the computing device 100 to the display devices 150 as appropriate. Although Figure 3 shows each bed or bay being associated with two adjacent display devices 150, the number and arrangement of the display devices 150 for each bay may vary according to circumstances. For example, if the ceiling tiles 211 are smaller and / or greater ceiling space was available, then there may be more display devices 150 used to present an image - thus instead of a 2x1 configuration of displace devices, there may be a 3x2 configuration of display devices (for example). Furthermore, although Figure 3 shows a one-to-one relationship between display devices 150 and ceiling tiles 211, it may be possible for a display device to span the space provided for two or more ceiling tiles 211. For example, in relation to bay 4, rather than having two display devices 150, one for each removed ceiling tile, there might be a single display device 150 that occupies the full space corresponding to the two removed ceiling tiles (provided this is mechanically compatible with the overall structure of the ceiling 210). In the example of Figure 3, the images displayed on the display screens provide sky views including clouds. In these images, the sky is bright and blue. This generally indicates a time of day and month in which the sun (not included in the displayed images) is relatively high in the sky - in contrast to a timing (of day and month) in which the sun is lower in the sky, when the sky is the likely to be less bright and have a reddish tinge. As discussed below, by changing the images displayed on devices 150 in Figure 3, this can indicate different times of the day and month, and so be used to adjust or support the circadian rhythms of a patient viewing the display devices 150. In some implementations, each system 10 may be implemented by a standalone system. For example, in the context of Figure 3, bay 3 may be provided with a system 10 including computing device 100 and display(s) 150, and likewise bay 4 may be separately provided with another system 10 including computing device 100 and display(s) 150. However, in other implementations, one system may be able to operate multiple display devices across different bays for different patients. A further consideration is that typically some hospital wards do not have windows, for example a critical care unit (CCU), a high dependent unit (HDU) and an intensive therapy unit (ITU). The display of images, for example of the sky, can generally provide comfort and reassurance to patients in such wards (in addition to the regular of circadian rhythms as described here). For example, the audio-visual systems and programs of system 10 as described herein may also be used to support all facets of CCU, HDU, high dose rate (HDR) treatment, recovery, dementia and mental health locations (inter alia) to alleviate stress, anxiety, and to assist in calming patients as well as inducing pain reduction. Figure 4 is a schematic diagram of another example of a system 10 for helping to regulate circadian rhythm as disclosed herein in which certain components are shared across multiple patients (bays). The system 10 of Figure 4 includes (by way of example) 6 display devices 150. The system 10 may be arranged such that each display screen 150 is assigned to a separate (respective) bay for a patient. In other implementations, one or more of the patient bays may be provided with multiple display screens. For example, the six display screens 150 may be split into 3 pairs of display screens 150, whereby each patient bay may be allocated a pair of display screens (analogous to Figure 3, in which bays 3 and 4 are each provided with a pair of display screens 150). Other configurations are possible, for example, the six display screens 150 of Figure 4 may be split into two pairs of display devices 150 and two individual display devices. In this configuration, a given image may be displayed both spread across a pair of two display devices and also on a single display device (in a more compressed format). The system of Figure 4 further comprises an uninterruptible power supply (UPS) 182 which allows system 10 to continue operation even in case there is a break in the power supply (such as from a power cut or the accidental removal of a plug from a socket). The UPS 182 may be sized and positioned for installation at an appropriate location for providing power as and when required to the various components of system 10. The system 10 of Figure 4 further comprises a master computer 100 (corresponding to the computing device 100 of Figure 1) and a touch screen 184 which is used as an input / output device to allow an operator to monitor, configure and control the operation of system 10. For example, the touch screen may be used by the operator to initiate and / or terminate the display of images on the display devices 150. The touch screen may also be used to provide status updates to the operator, for example, to indicate faulty or unexpected behaviour within the system 10. Each display device 150 is provided with a corresponding (respective) digital player 190 (also described as a digital media player). An HDMI connection 105 is provided from the master computer 100 to each display device 150 via a respective digital player 190. This HDMI connection therefore enables the master computer 100 to utilise the digital players 190 to display images on the respective display devices 150. The system 10 is also provided with universal serial bus (USB) connections 106 between the master computer 100 and the digital players. These USB connections can be used to provide power to and / or control the digital players 190 to display the images from the master computer 100 onto the display devices 150. In this architecture, the digital players 190 have the main responsibility for displaying the images or video on the display device 150, while the master computer 100 has more of a supervisory role, for example to configure the overall system, but with reduced or no direct involvement in the display of images per se. In some implementations, the system 10 includes a wall-mounted master switch to turn the system 10 off and on, including components such as the master computer 100, the touch screen 184, the digital players 190 and the display devices 150. The digital players 190 may be powered from the mains or potentially using the USB connectors 106. In some implementations, the digital players 190 shown in Figure 4 are BrightSign series 4 players (see https: / / www.briahtsign.biz / ), which are designed for high resilience and availability and have a customised (special purpose) operating system. These digital players 190 can be considered as custom-made computers which are specially design to play digital media and include a solid-state architecture, and an anodized aluminium which allows them to dissipate heat efficiently without the use of fans (such that the digital players 190 are smaller and quieter than many other computers). In some implementations, the system 10 is designed to have an auto reset timing function where the 24 / 7 image display program reboots every 7 days at 2am. The objective of this reboot is to maintain the program in a fresh and fault free condition. It will be appreciated that the interval between successive reboots, and the timing of such a reboot, can be adjusted as appropriate (compared to the values specified above) to take into account the circumstances of any given implementation. In some implementations, each patient receives the same sequence of images from the master computer (computing device) 100. For example, in the context of Figure 3, the pair of display devices 150 in patient bay 3 may be shown the same sequence of images as the pair of display devices 150 in patient bay 4. In this situation, all patients associated with system 10, such as all patients in a particular ward, may typically be presented with a sequence of displayed images that represents or mimics the natural lighting levels and colours synchronised to the local (solar) time. This configuration may be suitable for restoring circadian rhythms in patients whose natural circadian rhythms have been disrupted such as by an anaesthetic or major illness. In some cases, the treatment supplied by system 10 may be more customised to individual patients. For example, if the current circadian rhythm of a patient appears to be lagging local solar time, the image sequence presented by the display devices may be configured to a circadian rhythm having a phase which is intermediate between (i) the current circadian rhythm of the patient, and (ii) the local solar time. The image sequence presented by the display devices 150 may then be slowly advanced in phase until it ultimately becomes aligned with the local solar time. In effect, such an approach may guide or facilitate the circadian rhythm of the patient to return to local solar time in a series of steps. In developing and utilising system 10, we note that the terrestrial environment is dominated by 3 main cycles. The annual cycle is defined by the orbital period of the earth around the sun of approximately 365 days. The annual cycle has significant consequences for nature, such as the flowering of plants, but the long period of this cycle means that it is generally not impacted by more short-term timing variations. The monthly cycle is defined by the orbital period of moon around the earth. The location of the moon can be significant for some natural organisms, such as those influenced by tides, but is of lesser significance for humans. For present purposes, the most important cycle is the daily 24 hour (solar) cycle which arises from the rotation of the earth. This rotation causes the sun to apparently follow a circular path about the earth. Typically, for any given location and time, a first portion of the path is above the horizon and a second portion of the path is below the horizon. If the sun is in the first portion, the given location is experiencing daytime, while if the sun is in the second portion, the given location is experiencing nighttime. The rotational axis of the earth is offset to the plane of the ecliptic (as defined by the orbit of the earth about the sun). This offset means that each day, for any given location on the earth (except the north and south poles), the location in effect goes through a rotational cycle of moving closer to the ecliptic and then away from the ecliptic. If the portion of the cycle which is closer to the ecliptic happens during daytime, the location is in summer, with longer daylight and the midday sun higher in the sky. Conversely, if the portion of the cycle which is closer to the ecliptic occurs during nighttime, the location is in winter with shorter daylight and the midday sun lower in the sky. Accordingly, the position and path of the sun are determined not only the daily rotation of the earth about its axis, but also by the year orbit of the earth about the sun. At a given latitude in the northern hemisphere (outside the polar regions), the sun will rise in the morning in the east, and move upwards to a peak height due south at midday (solar time). After midday, the sun will in effect follow a mirror image of the morning, falling to (and then below) the western horizon. Comparing summer to winter, in summer the path of the sun above the horizon is longer, with the sun rising earlier in the northeast, reaching a maximum (peak) at midday, and setting later in the northwest. By comparison, for winter, the sun rises later in the southeast, has a lower peak at midday, and sets earlier in the southwest. The main factors impacting the solar path are time of year, as above, and latitude. At low latitudes, the seasonal variation is relatively small - the sun’s path is approximately due east to due west, rising at midday to overhead. In contrast, at high latitudes the seasonal variation is much more pronounced, especially in relation to duration of the day, with the polar regions inside the arctic and Antarctic circles being informally described as the “land of the midnight sun”. In contrast, the longitude of a location does not change the path of the sun, but rather changes the timing (phase) of the solar cycle to accounting for different time zones around the globe. Accordingly, the solar path used by the system 10 can be determined based on current time of year, current latitude, and either longitude or (equivalently) time difference between the local time zone and UTC The elevation of the sun, as determined according to solar path, affects both the intensity (brightness) of received sunlight and also the colouring. Both of these changes relate to the sunlight having an increasingly long path through the atmosphere for lower elevations of the sun. In particular, the earth’s atmosphere is mostly transparent to visible radiation, but there is a certain amount of Rayleigh scattering caused by sunlight scattering from molecules in the atmosphere. Rayleigh scattering is wavelength (A) dependent (based on A-4). In particular, the increased Rayleigh scattering of shorter, bluer wavelength light (compared to redder, longer wavelength light) produces the blue coloration of the sky, especially for higher elevations of the sun. When the elevation of the sun is relatively low, the loss of blue light increases so that most blue light is lost (e.g. multiply scattered) and may not reach a viewer. This leaves a person receiving light which is more attenuated (less bright) and which also has an apparent reddish coloration. The reddish colouring may be further emphasised by scattering due to dust and other aerosols suspended in the atmosphere such that the sky (as well as the sun) may have a reddish coloration. This reddish colouring of sunlight at low solar elevation (dusk and dawn) is generally considered to provide a gentler and “warmer” feel. The gentler feel may arise because less sunlight is being received at dusk and dawn (compared to the middle of the day) due to the longer optical path through the atmosphere for lower elevations of the sun. The ‘warmer’ feel may be parameterised in terms of a colour temperature (see https: / / en.wikipedia.org / wiki / Color_temperature) based on Wien’s law, which provides a linkage between wavelength and temperature. In other words, different colours are associated with different temperatures. For example, red is associated with a lower temperature than yellow. Although technically Wien’s law relates to black body radiation, the concept of colour temperature has been applied more widely. Thus in the context of sunlight, the red light at sunrise or sunset (which is produced by filtering) is considered to have a lower colour temperature than the yellow or white light from the sun at a higher elevation. The red lighting for sunrise / sunset may be perceived as warm, whereas yellow or white light may be perceived as a hotter (and potentially harsher) form of lighting. The reddish lighting at sunrise and sunset is typically considered to correspond to a ‘warm’ colour temperature of around 5000K, while the whiter midday lighting may have a hotter colour temperature of 6500K. The change in colour temperature over the course of the day from warm to hot then back to warm parallels the change from dark to light and then back to dark. These changes in both light intensity and also colour temperature provide significant external cues for maintaining the human circadian rhythms in line with the solar day. The sequence of images presented by the computer device 100 on the display device 150 are selected to reflect or mimic the solar cycle allowing for: (i) the present time of year, and (ii) the present geographical location; and local time relative to UTC. The first of these parameters can be obtained from any network source (GPS, mobile phones, data networks, etc). The use of GPS or other similar services for the first parameter has the advantage that this time determination can be implemented without any requirement for WiFi or internet access (which might complicate installation of system 10 in a hospital environment). The second and third parameters are fixed for the location, and can be readily obtained from multiple sources as a one-off piece of information at installation which does not then need subsequent updating. The system 10 provides images on the display device(s) 150 that mimic the daily cycle of solar illumination and hence provide the patient 230 with a strong environmental indication of the circadian cycle. The displayed images take into account: a) the effect of solar elevation on intensity b) the effect of solar elevation on colour temperature c) the variation of solar elevation with date and time, which is a function of position of the observing site (longitude and latitude). It will be appreciated that the images are generally not of the sun itself, but rather of objects such as scenery illuminated by light from the sun which is positioned at the appropriate solar elevation. For example, if the sun is relatively low in elevation, then the light intensity of the image will be generally reduced compared to when the sun is at a relatively high elevation. Similarly, if the sun is relatively low in elevation, the colour temperature of the image will be generally reduced (to a warmer, redder colour) compared to when the sun has a relatively high elevation. The system 10 may be used to set the colour temperature to replicate real daylight. Typically, this is achieved by determining the solar elevation for the time of interest (such as the present) and selecting an image corresponding to this solar elevation. The colour temperature of the selected image is then represented in the selected image because the selected image matches the appropriate image and hence colour temperature. Having a sequence of images (scenes) which display colour temperature in this manner provides an interaction with the pineal gland in the supercharismatic nucleus in the hypothalamus. Figure 5 is a flowchart illustrating an example of using a system such as shown in Figure 1 to help regulate the circadian rhythm as described herein. The method of Figure 5 may be implemented within a device such as shown in Figure 4 which provides imaging to multiple patients (for example, 6 patients), or within a device that supports only a single patient. It will be appreciated that the flowchart of Figure 5 not limiting, and various components of the flowchart may be modified or omitted according to the particular circumstances. In operation 510, the system maintains a set of images having solar illumination. Typically these images are of some relatively peaceful and natural subject, for example clouds in the sky (see Figure 3), trees, a beach, and so on in natural sunlight. The images are generally still images, but may comprise videos (or animated images such as GIF files) or a combination thereof. Each image corresponds to a given (known) solar elevation, in other words the given solar elevation represents the height of the sun when the image was acquired. Accordingly, each image is stored with (or indexed to) the known solar elevation, either by storing the elevation per se, or else by storing information that allows the elevation to be determined (such as location of acquiring the image and time of year). In most implementations, it is expected that at least some of the images are photographs which were taken when the sun was at various elevations. In some cases, additional images may be generated by interpolating between photographs. For example, if images are acquired at elevations of 48, 49, 50 degrees and so on, interpolated images may be created for elevations of 48.5 and 49.5 degrees (and so on). As another form of interpolation, the colour temperature of an image may be artificially changed, such as by using a computer. Various image processing packages provide a facility to adjust colour temperatures in this manner. Such an approach allows a user (creator) to initially acquire a relatively small set of images, in effect with relatively large gaps between the images in terms of solar elevation. The adjustment of colour temperatures allows images to be created to fill in the gaps, so that lighting changes from solar elevation can be tracked closely and accurately. It is also possible for at least some of the images to be at least partly created, whether by a human or by an artificial intelligence (Al) system. Information about Al sky simulation can be found, for example, at: https: / / developer.nvidia.com / gpugems / gpugems3 / part-ii-light-and-shadows / chapter-13-volumetric-light-scattering-post-process. This creation is generally performed in advance to provide a set of stored images. It would also possible for the Al system to generate images in real-time as they are to be displayed, however, the calculations are non-trivial. Therefore, creating the images in advance will generally be more efficient, since an image for a given solar elevation, once created, may be used repeatedly over successive days (whenever the solar elevation corresponds to that image). It will be appreciated that overall the number of images in the sequence may be quite high to be able to impart a natural (real-life) movement of the sun. At operation 520, the current location, date and time may be determined and this can then be used calculate the current solar elevation. This determination may extend over a range of times and corresponding solar elevations to reflect the solar movement over the specified time period (say the next 3 hours). The solar elevation may therefore be determined over this period and corresponding images identified accordingly. At operation 530, the parameters of the circadian timing are set. In many cases, this circadian timing reflects the current solar elevation and solar cycle. However, in some cases the circadian timing may differ from the solar cycle as described in more detail below. At operation 540, the appropriate solar images are accessed and displayed on the display device(s) 150. As noted above, in many cases the appropriate solar images for display and access are those corresponding directly to the solar cycle (for the location of the hospital which includes the system 10). In other words, the solar information obtained at operation 520 is used to access an image representing or matching the current solar elevation, or a sequence of images corresponding to the solar path and associated elevation, for some upcoming time period (say the next 3 hours). In some implementations, each image is displayed for a fixed period. A given image may be displayed more than once (each time for the fixed period), if the solar elevation is changing relatively slowly, such as might typically be the case around midday for the maximum of solar elevation. At operation 550, the system transitions from one image to the next image in synchronism with the circadian cycle (typical the solar cycle). In other words, we assume that a first image is displayed at time T1, and a second image is to be displayed at time T2 which is (say) 2 minutes after T1 (and likewise a third image at time T3, and so on). The system determines the solar elevation for times T1, T2 and T3, and uses this elevation to identify corresponding images 11, I2 and I3 having matching respective solar elevations. The system is then able to display image 11 at time T1, I2 at time T2, and I3 at time T3. It will be appreciated that the movement of the sun in the sky is relatively slow over many hours, so there might be a relatively large number of images involved in this process throughout the day. As noted above, the identification of images corresponding to a given time may be performed repeatedly as each new timing commences. Alternatively, a sequence of corresponding images may be determined spread across an upcoming period. In either case, the system 10 is able to display the images corresponding to circadian scenes so that scene changes follow the correct solar timing (or an adjusted timing as discussed further below). As noted above, the images for display may comprise still images, animated images, or video (or a combination thereof). The use of video uses more processing resources, so the presentation of still and / or animated images may be more efficient for displaying views that are intended to be peaceful and calm (rather than high action). The system 10 may support various facilities to support a transition from one image to another image, such as melting, sliding and so on. Such transitions are well-known to the skilled person such as from presentation applications. As discussed above, the displayed images may correspond to the local solar cycle for aligning (or restoring) the circadian cycle of a patient in synchronism with the local solar cycle. However, more complex alignments may be performed. For example, we assume that a post-operative patient has a circadian cycle which is 6 hours ahead of the local solar cycle. In such circumstances, adjustable circadian timing may be used to reset the body clock of such a patient and negate the effects of post-operative delirium. More particularly, in this example, the circadian cycle of the display images may be used to slow down the circadian cycle of the patient to allow the solar cycle to catch up and aligned with the circadian cycle of the patient. One strategy for achieving this would be to use the system 10 to simulate a circadian cycle based on a 25 hour day by slowing down the presentation displayed to the user (who is not exposed to the solar cycle). For example, rather than displaying each image to the user for 2 minutes (120 seconds) as mentioned above, the same set of images may each be displayed for 125 seconds. After 6 days, the circadian cycle experienced by the patient is now aligned with the solar cycle, and hence the patient can now be exposed to the local solar cycle. It will be appreciated that this realignment / resynchronisation can be performed in different ways. For example, rather than presenting each image for 125 second rather than 120 seconds, the image duration in another strategy may be maintained at 120 seconds, but the number of images to be presented to the user for a 25 hour ‘day’ would increase. For example, in a 24 hour day, there are 720 2-minute periods, whereas a 25 hour ‘day’ has 750 2-minute’ periods. The (apparent) solar cycle would then have to be adjusted such that each of the “two-minute” periods corresponds to 115.2 seconds for tracking through the solar elevations to display to the user. In other words, for every two minutes displayed to the patient, the solar elevation is advanced by an amount corresponding to 115.2 seconds of the true (24 hour) solar cycle. It will be appreciated that the system 10 may support a user (operator) in determining the best way or strategy to perform such phase (re)alignments. For example, a user may enter the current phase of the circadian cycle for a patient, and the system 10 automatically determines a patient-specific schedule of day lengths and phases to realign the patient with the solar cycle in the most appropriate manner (such as quickly, but with minimal distress or discomfort for the patient). In some implementations, a trigger point may be defined to allow one scene (image) to blend into a previous scene or image without frame stoppage. The system may also allow a user (operator) to seamless loop a scene to extend or shorten the overall duration (such as described above), where such looping may be controlled by using the trigger points. In addition, the system supports programmed switching with delay or advancement buttons, such that the day-length cycle may be adjusted, for example in 10min segments up to 4 hours. This facility allows the user circadian cycle to be set differently from the current local solar cycle. With this facility, the day is controllable and adjustable as discussed above for each patient to support a gradual body clock realignment. As mentioned above, the system 10 may be used post-operatively to help realign the circadian rhythm of the patient with the (local) diurnal rhythm. This use of system 10 can be considered as supporting a recovery mode for a patient. Conversely, the system 10 may also be used in a pre-operative fashion to support an upcoming procedure. In this latter context, the system may implement an anaesthetic mode which seeks to reduce physiological and metabolic activity at the time of the operation. For example, if an operation is scheduled at 9 am in two days’ time, the system 10 may expose the patient to a longer (say 26 hour) circadian rhythm. This would then cause the 9 am surgery time to correspond (approximately) to 5 am in the patient time-frame based on the shifted circadian rhythm. Since the patient is naturally more asleep at 5am than at 9am for a normal diurnal circle, the administration of anaesthetic at this time may be less disruptive for the patient (compared to if their circadian rhythm had not been realigned). It will be appreciated that a patient may benefit from system 10 providing firstly the anaesthetic mode (pre-operative) and then also from system 10 providing the recovery mode (post-operative). In conclusion, while various implementations and examples have been described herein, they are provided by way of illustration, and many potential modifications will be apparent to the skilled person having regard to the specifics of any given implementation. Accordingly, the scope of the present case should be determined from the appended claims and their equivalents. References [1] “Circadian photoreception in the retinally degenerate mouse (rd / rd)” by RG Foster et al, in J Comp Physiology A. 1991 Jul;169(1 ):39-50. [2] “Melanopsin: An opsin in melanophores, brain, and eye” by Provencio et al, in Neuroscience January 6, 1998 95 (1) 340-345. [3] “Short-wavelength light sensitivity of circadian, pupillary, and visual awareness in humans lacking an outer retina” by Zaidi et al, Current Biology 2007 Dec 18;17(24):2122-8.

Claims

1. A computer-implemented system for regulating the circadian rhythm of a human subject, the system including a computing device and a display device, the computing device5 having a processor configured to:determine solar elevations for a specified time period and select a sequence of images corresponding to the determined solar elevations;access a set of images, each image corresponding to a solar elevation and providing a view indicative of the corresponding solar elevation, wherein each image has a colour10 temperature which matches the solar elevation corresponding to the image; and display on the display device to the human subject the sequence of images from the set of images to provide a sequence of views indicative of a change in solar elevation with time, the sequence of images corresponding to a system circadian cycle which is intermediate: (i) the current circadian cycle for the human subject, and (ii) the local solar15 cycle.

2. The system of claim 1, wherein the set of images have corresponding solar elevations which span the range of solar elevations visible from a physical location of the human subject.CM3. The system of claim 1 or 2, wherein the set of images provide views with solar illumination, wherein the solar illumination for an image utilises the solar elevation corresponding to the view for that image.25 4. The system of any preceding claim, wherein a first image in the set of images hasbeen processed to produce a second image by changing the colour temperature of the first image such that the second image corresponds to a different solar elevation from the first image.30 5. The system of any preceding claim, wherein displaying a sequence of imagesmatching the change in the colour temperature of daylight provides an interaction with the pineal gland in the supercharismatic nucleus in the hypothalamus.

6. The system of any preceding claim, wherein each image has a brightness which35 matches the solar elevation corresponding to the image.

7. The system of any preceding claim, wherein the system further comprises a store holding the set of images, and wherein the system is configured to access the sequence of images for display from the store.5 8. The system of any preceding claim, wherein the system comprises a network sourcehaving GPS.

9. The system of any preceding claim, wherein the system further includes one or more customised players for displaying the sequence of images to the human subject, optionally10 wherein the customised player includes a bespoke operating system.

10. The system of any claim 9, wherein the system is configured to re-boot automatically after a predetermined period, optionally wherein the predetermined period is a week and the re-boot is configured to occur at night.1511. The system of any preceding claim, wherein the system is configured to display a LO sequence of images corresponding to the local solar cycle.CMCQ 12. The system of any one of claims 1 to 10, wherein the system further includes a20 facility for increasing or decreasing the day length of the system circadian cycle, optionally C\j wherein the facility comprises a screen with buttons for an operation to press to increase or reduce the day length.

13. The system of any one of claims 1 to 10 or 12, wherein the system is configured to 25 determine a strategy for the system circadian cycle to realign the current circadian cycle for the human subject to the local solar cycle.

14. The system of claim 13, wherein the strategy to realign the current circadian cycle for the human subject comprises using a system circadian cycle having a day which is less than 30 or greater than 24 hours, optionally wherein the system circadian cycle increases or reduces the duration of display of images in the set of images to provide the day which is less than or greater than 24 hours.

15. The system of claim 14, wherein the realignment of the circadian cycle may be35 performed pre-operatively in an anaesthetic mode and / or post-operatively in a recovery mode.

16. The system of any preceding claim, wherein the system is configured to have a void above the display device.

17. The system of any preceding claim, wherein the display device includes a non-5 reflective layer configured to face the human subject.

18. The system of any preceding claim, wherein at least a portion of the system is configured to link to or be incorporated into a bedhead trunking system10 19. The system of any preceding claim, wherein the system includes a hand-held controlunit to allow the human subject to perform at least one of the following:(i) turn the display device 150 off or on; and / or(ii) control the brightness of the output from the display device.15 20. A computer-implemented method for regulating the circadian rhythm of a humansubject, the method comprising:determining solar elevations for a specified time period and selecting a sequence of images corresponding to the determined solar elevations;accessing a set of images, each image corresponding to a solar elevation and20 providing a view indicative of the corresponding solar elevation, wherein each image has a colour temperature which matches the solar elevation corresponding to the image; anddisplaying on the display device to the human subject the sequence of images from the set of images to provide a sequence of views indicative of a change in solar elevation with time, the sequence of images corresponding to a system circadian cycle which is25 intermediate: (i) the current circadian cycle for the human subject, and (ii) the local solar cycle.

Images