Control of lighting systems for color point and flux level control

Abstract

A method is provided for controlling a multi-channel lighting system in which (nominal) color point information about the light source is adjusted based on a temperature estimate and the desired current drive level. Therefore, this method individually compensates for the effects of light source temperature and the calculated current drive level on color point and flux. An iterative loop finds the current drive level to achieve the desired color point and flux.

Description

Technical Field

[0001] This invention relates to the control of lighting systems, and more particularly to achieving flux level control (i.e., dimming) while maintaining a desired color point. Background Technology

[0002] Multichannel lights achieve color point control by including different channels with different color points and independently controlling the drive level applied to each channel.

[0003] For example, the use of pulse width modulation (PWM) dimming in multi-channel lamps is well-known, especially for LED lamps. PWM dimming is very attractive because LED behavior is highly predictable. In particular, the same current is always driven through the LED, and changing the dimming level only involves selecting the duration for which the lamp is on. By selecting a PWM control signal of a sufficiently high frequency, on / off cycles imperceptible to the human eye can be achieved.

[0004] However, there is growing concern about flicker, an inherent drawback of PWM dimming at low PWM frequencies (which are less costly to implement). Furthermore, the integrated circuit (IC) industry is increasingly focused on ICs with amplitude modulation dimming capabilities.

[0005] PWM dimming systems use a fixed current, so as mentioned above, no current correction is required (i.e., color point correction based on current). However, it is common practice to correct the color point of each channel for temperature (e.g., the XYZ values ​​in the CIE 1936 color space), especially when using direct red LEDs.

[0006] In order to use mainstream amplitude dimming ICs and achieve the desired control of the output color point of the lighting system, the current effect becomes a problem in achieving accurate color point control.

[0007] CA2791258A1 discloses a method for operating a lighting apparatus comprising a plurality of discrete lighting sources having distinguishable color coordinates. The method includes determining a target color coordinate and luminous flux for operating the lighting apparatus; determining an input electrical power value for each of the plurality of discrete lighting sources substantially generating the target color coordinate and luminous flux by referring to a calibration data lookup table having calibration data based on measurements of the plurality of discrete lighting sources; determining, according to the calibration data, a color mixing region in which the target color coordinate is located, defined by three distinguishable color coordinates of the plurality of discrete lighting sources; and determining a luminous flux ratio of each of the plurality of discrete lighting sources having one of the three distinguishable color coordinates that defines the color mixing region substantially generating the target color coordinate.

[0008] US2010 / 301777A1 discloses a method for temperature-dependent adjustment of the color or photometric characteristics of an LED lighting device having LEDs that emit light of different colors or wavelengths or LED color groups that emit light of the same color or wavelength within a color group, wherein the luminous flux portion determines the color, color temperature, and / or chromaticity coordinates of the light emitted by the LED lighting device.

[0009] US2010 / 259182A1 discloses a light source comprising one or more first light-emitting elements for generating light having a first wavelength range and one or more second light-emitting elements for generating light having a second wavelength range. The first and second light-emitting elements are responsive to separate control signals provided to them. A control system receives signals representing operating temperature from one or more sensing devices and determines the first and second control signals based on the desired color of light and the operating temperature. Light emitted by the first and second light-emitting elements as a result of the received first and second control signals can be mixed to substantially obtain light of the desired color. Therefore, the generated light of the desired color can be substantially independent of changes in the operating characteristics of the light-emitting elements caused by junction temperature. Summary of the Invention

[0010] This invention is defined by the claims.

[0011] According to an example of one aspect of the present invention, a method for controlling a lighting system is provided, the lighting system comprising a plurality of lighting channels, the plurality of lighting channels comprising light sources having different color points, the method comprising:

[0012] The first step is to receive color point information, which includes nominal color point information about the light source.

[0013] The second step is to adjust the color point information based on the latest temperature estimate.

[0014] The third step is to further adjust the color point information based on the latest current drive level for the corresponding lighting channel, wherein the second and third steps can be performed in any order.

[0015] The fourth step involves using further adjusted color point information to determine the flux contribution of each illumination channel in order to achieve the desired combined color point and combined light output flux from multiple illumination channels.

[0016] The fifth step is to update the current drive level for multiple lighting channels to create an updated current drive level that accounts for the flux contribution of each lighting channel.

[0017] The sixth step is to update the temperature estimate based on the updated current drive level to create an updated temperature estimate; and

[0018] Repeat steps two through six if necessary.

[0019] This method determines the current drive levels of a set of channels to achieve a desired color point and desired brightness (e.g., dimming level), but ensures that the effect of operating channels with different currents on the resulting color point is taken into account. Color point control and brightness level (i.e., dimming level) control are implemented such that the color point remains constant across all brightness (i.e., dimming) levels. This provides an analog current level control method that can be used alone or in combination with digital (PWM) current level control.

[0020] The first compensation measure is to determine the temperature generated by different drive currents (e.g., LED junction temperature), and this is used to model how the color point will change. This temperature compensation is known.

[0021] The method of this invention also takes into account the fact that different color points in the illumination channel require different drive currents. In particular, blue and green LEDs exhibit considerable color shifts. Therefore, the color point information is updated additionally based on the current drive level of the corresponding illumination channel. This can be achieved in various ways, for example, depending on the type of light source.

[0022] Due to color shift, the balance of different channels needs to be adjusted to achieve the desired setpoint for the complete light source. Another impact is that drive current and flux are non-linearly related, especially when a wide range of possible drive currents exists. Part of this non-linearity is due to inherent effects within the LED die. All these effects manifest as variations in flux relative to current, thus requiring different current drive levels to achieve a given flux.

[0023] Color shifts are independent of temperature, so they are modeled as independent effects (which can be corrected in any order), and individual temperature control loops cannot provide full compensation.

[0024] Therefore, in addition to temperature compensation, the method of this invention allows for the separate consideration of the relationship between nonlinear flux and current, as well as the variation of the color point with current. The method is iterative, repeating the steps until sufficient color point control accuracy is achieved.

[0025] Repeat steps two through six until:

[0026] Temperature estimates converge to values ​​that deviate less than a threshold when updated; and / or

[0027] The current-driven level converges to a value that deviates less than the threshold when it is updated.

[0028] In one embodiment, steps two through six are repeated until the temperature estimate converges to a value less than a threshold when it is updated, and the current drive level converges to a value less than a threshold when it is updated.

[0029] Therefore, this method can iteratively obtain a set of correct color points (and output flux) based on accurate temperature estimation and by properly adapting the current drive level to compensate for the influence of the current drive level on the color points.

[0030] The second step may include transforming the CIE 1936 XYZ color coordinates to CIE xy chromaticity color coordinates, applying temperature correction to dx / dt and dy / dt, and transforming back to XYZ color coordinates.

[0031] This provides an effective method for achieving temperature compensation.

[0032] In one approach, the third step may include using information related to the rate of change of the CIE xy chromaticity color coordinates relative to the drive current.

[0033] This method for modeling the dependence of color on drive current is particularly well-suited for phosphor-converted LEDs.

[0034] In another method, the third step may include:

[0035] The first sub-step is to derive the representative wavelength for the adjusted color point information;

[0036] The second sub-step involves adjusting the representative wavelength based on the latest current drive level for the corresponding illumination channel; and

[0037] The third sub-step involves further adjusting the color point information based on the already adjusted representative wavelength.

[0038] This method for modeling the dependence of color on drive current is particularly well-suited for direct LEDs. In this way, the method takes into account the different drive currents required for the dominant wavelength.

[0039] The first sub-step, for example, uses a model for converting from a color point to a representative wavelength. The representative wavelength is the dominant wavelength for that color point. For example, the dominant wavelength is defined by drawing a line (in CIE color coordinate space) through the white point and its x, y coordinates. The wavelength at which the line intersects the boundary of the color space is the dominant wavelength.

[0040] The second sub-step, for example, uses a current-dependent model for different wavelengths and a model based on the CIE x,y color coordinates as a function of the dominant wavelength to determine the color point offset with wavelength.

[0041] The third sub-step, for example, uses a model for converting representative wavelengths to color points.

[0042] Therefore, the second and third steps convert between current and wavelength, so that the relationship between wavelength and current can be used.

[0043] The method may also include applying pulse width modulation to the drive current for the lighting channel. Therefore, an analog drive current scheme can be combined with a PWM drive scheme. The PWM setting (for one or more channels) can, for example, be set to 1. Thus, channel differentiation is achieved through PWM control with the longest possible duty cycle, and further scaling uses amplitude modulation control.

[0044] The present invention also provides a method for controlling a lighting system, the lighting system including multiple lighting channels, the multiple lighting channels including light sources with different color points, the method comprising:

[0045] For the first range of dimming levels, apply the simulation method defined above; and

[0046] For the second range of dimming levels, pulse width modulation dimming is applied.

[0047] Therefore, the above method (which is an analog dimming method) can be combined with PWM dimming based on the applied dimming level.

[0048] The first range is for low brightness levels, and the second range is for high brightness levels.

[0049] In this first method, PWM dimming can be initially used (for high brightness), and the above method can also be used for low brightness levels. This improves resolution at low brightness.

[0050] Alternatively, the first range can be for high brightness levels, and the second range for low brightness levels.

[0051] In this second method, analog dimming can be initially used (for high brightness) to avoid flicker, and PWM dimming can be used for low brightness levels. This reduces the dimming range required for analog dimming and improves the accuracy of the analog dimming model.

[0052] The present invention also provides a computer program including computer program code, which, when run on a computer, is adapted to implement the above-described method.

[0053] The present invention also provides a processor for controlling a lighting system comprising multiple lighting channels, the multiple lighting channels comprising light sources having different color points, wherein the processor is programmed using the computer program defined above.

[0054] A lighting controller may include the processor described above.

[0055] The present invention also provides a lighting system comprising: multiple lighting channels, each lighting channel including a light source with a different color point; and

[0056] The lighting controller defined above is used to control the drive current to different lighting channels.

[0057] These and other aspects of the invention will become clear from and will be set forth with reference to the embodiments described below. Attached Figure Description

[0058] To better understand the invention and to more clearly illustrate how to implement it, reference is now made to the accompanying drawings by way of example only, in which:

[0059] Figure 1 A known method for determining the flux level of a single channel, taking temperature into account, is shown;

[0060] Figure 2 The CIE chromaticity diagram is shown, and the effect of amplitude modulation dimming on phosphor-converted LEDs is also shown.

[0061] Figure 3 The typical relationship between relative flux (y-axis) and relative current (x-axis) per relative current is shown;

[0062] Figure 4 The color point shift of the lighting system at a 2% dimming level is shown;

[0063] Figure 5 The first option within the method of controlling the lighting system is shown;

[0064] Figure 6 It shows Figure 5 The second option within the method;

[0065] Figure 7 It shows how to determine the channel fraction;

[0066] Figure 8 This illustrates methods that can be used to combine amplitude modulation and PWM; and

[0067] Figure 9 The lighting system is shown. Detailed Implementation

[0068] The invention will be described with reference to the accompanying drawings.

[0069] It should be understood that while exemplary embodiments of the indicated devices, systems, and methods are provided, the detailed descriptions and specific examples are intended for illustrative purposes only and are not intended to limit the scope of the invention. These and other features, aspects, and advantages of the devices, systems, and methods of the present invention will be better understood through the following description, the appended claims, and the accompanying drawings. It should be understood that these drawings are merely schematic diagrams and are not drawn to scale. It should also be understood that the same reference numerals are used in the drawings to indicate the same or similar parts.

[0070] This invention provides a method for controlling a lighting system in which (nominal) color point information about the light source is adjusted based on a temperature estimate and the desired current drive level. Therefore, this method individually compensates for the effects of the light source temperature and the calculated current drive level on color point and flux. An iterative loop finds the current drive level to achieve the desired color point and flux.

[0071] Figure 1 A known method for determining the flux level of a single channel, taking temperature into account, is shown. The drive current is derived from the flux level.

[0072] The method begins at step 10. The inputs to the flowchart include the nominal color points 12 of the individual LEDs under reference conditions. These nominal color points are provided, for example, as CIE 1931 XYZ coordinates for calculation. However, the color point information can be processed in another color space.

[0073] In step 14, the XYZ coordinates are temperature-corrected based on a temperature estimate, which is used as the initial temperature estimate in step 16 and is generated by the method in subsequent iterations, as will be clear from the explanation below.

[0074] Given the target color and flux provided as input 18, the relative flux contribution of each channel in the channel can be calculated in step 20.

[0075] Based on the computational flux requirements, the LED temperature can be estimated in step 22. This takes into account the temperature dependence model 23. The convergence of the temperature estimate is checked in step 24. If the estimated temperature has not yet converged with the previous temperature estimate, the method returns to the XYZ correction step 14.

[0076] When convergence occurs, the process ends in step 28.

[0077] This invention extends temperature compensation to achieve current amplitude modulation, and in particular, makes it possible to compensate for the effects of non-constant drive current on color points.

[0078] The effects of amplitude modulation dimming were analyzed for typical red, green, and blue LEDs. Blue and green LEDs, in particular, showed significant color shifts with dimming.

[0079] Figure 2 The CIE chromaticity diagram is shown. Regions 30R, 30G, and 30B illustrate how the color points of red, green, and blue LEDs shift due to a dimming level change from 100% to 0.1% for phosphor-converted LEDs. Different points represent different dimming levels. It can be seen that the color point shift is most pronounced for blue and green LEDs.

[0080] In addition to color point shift, LEDs also exhibit nonlinear behavior between output flux and current, especially over a large current range.

[0081] Figure 3 The graph illustrates the relationship between typical relative flux (y-axis) and relative current (x-axis) per relative current. It shows the variation in the slope of the relative flux versus relative current curve. As indicated, this relationship is non-linear.

[0082] Applying known color point control algorithms with temperature compensation, but ignoring flux and color point shift with current, will result in significant color shift in LED devices.

[0083] Figure 4 The color point offset of the lighting system at a 2% dimming level is shown. The crosshairs in area 40 indicate the color point offset for target color points of 2700K, 4000K, and 6500K. The target color points are located on solid lines. The offset is approximately twice the allowable color point deviation specified in ANSI.

[0084] The conclusion that can be drawn is that without proper compensation for the nonlinearity of flux with current, the combination of amplitude modulation dimming and color point shift will not result in acceptable color consistency.

[0085] This invention provides a suitable method for correcting the nonlinear behavior of flux and color point with current. The invention provides additional features to be added to corrections for known temperatures. Therefore, the aim is to describe the change in color point (e.g., as XYZ coordinates) as a function of temperature and current.

[0086] Figure 5 and Figure 6 A method for controlling a lighting system is shown, the lighting system comprising multiple lighting channels, each of which includes a light source with a different color point.

[0087] The method begins at step 50 and then includes a first step of receiving nominal color point information 51 about the light source. In a second step 52, the color point information is adjusted based on a temperature estimate. This temperature estimate is later derived and fed back into the method, thus forming an iterative loop. Therefore, the temperature estimate is updated during each iteration, and the temperature correction is based on the latest (i.e., most recent) temperature estimate (or the initial estimate at the start of the method).

[0088] For example, temperature correction involves transforming the CIE 1936 XYZ color coordinates to CIE xy Y chromaticity color coordinates and applying temperature correction to dx / dT and dy / dT as well as the flux level. This provides an efficient (known) way to achieve temperature compensation. The formula for the transformation is generally known and is given by:

[0089] X = x / y

[0090] Y = Y

[0091] Z = (1 - xy) / y

[0092] In this example, the output of step 52 is the xyY value.

[0093] Figure 5 and Figure 6 The flowchart includes two possible correction methods: one based on the dependence of x and y chromaticity values ​​on current, and the other based on the dependence of wavelength on current.

[0094] Step 53 determines whether the calibration is based on wavelength or current. Then, Figure 5 The only steps of the current-based correction method are shown. Figure 6 Alternative paths using this method are shown. The first steps (50, 52, 53) and the final steps (61, 62, 64, 66, 70) are common to both paths using this method.

[0095] Note that the present invention may provide a system having only one of these two methods, or it may provide a system that allows for selection, such as... Figure 5 and Figure 6 As shown.

[0096] Step 54 (used in both methods but with different steps) involves further adjusting the color point information based on the current drive level of the corresponding lighting channel. This current drive level is also derived and fed back in a later flowchart, thus forming an iterative loop again. Therefore, the current setting is updated during each iteration, and the color point adaptation taking into account the current level is based on the latest (i.e., most recent) current setting.

[0097] The first-order approximation used to correct the color point will be used to apply a linear relationship between the color point and the current, thus using factors dx / dI and dy / dI.

[0098] If the data is in XYZ format, it can be converted to xyY format. Then... Figure 5 The third step, 54, includes using information related to the rate of change of the CIE xy chromaticity color coordinates with respect to the drive current in step 80. This method for modeling the dependence of color on drive current is particularly suitable for phosphor-converted LEDs.

[0099] Step 61: Convert back to XYZ coordinates.

[0100] Step 4, 62, involves using further adjusted color point information to determine the flux contribution of each illumination channel in order to achieve the desired combination of color points and combined light output flux from multiple illumination channels.

[0101] In step 62, nonlinear flux relationships can be compensated (such as...). Figure 3 (As shown). The flux variation with current and temperature is directly modeled as Y = Y(I, T).

[0102] Step 4, 62, provides a set of relative flux fractions in the form f1…fn for the n-channel system. The relative flux fractions indicate how much flux each channel should produce to meet the target flux. The value f is between 0 and 1. If the target color point values ​​X, Y, Z and the X, Y, Z values ​​of the LEDs (after temperature and current compensation) result in a value f greater than 1, the target is unattainable and needs to be scaled.

[0103] For each channel, to form this set of desired flux levels, step 5, 64, involves updating the current drive levels of the multiple lighting channels to create updated current drive levels. These are the current levels required to achieve the defined flux contribution for each lighting channel. These current levels are fed back to step 80.

[0104] Considering the nonlinear nature of the color point offset with current in direct LEDs, the offset can be alternatively modeled as the rate of change of wavelength as the offset of dλ / dI.

[0105] Based on these updated current levels, step 66 involves updating the temperature estimate to create an updated temperature estimate. This uses a temperature-dependent model 68.

[0106] In step 70, a convergence test is performed to determine if the iterative process can be stopped. If convergence occurs, the method terminates in step 72; otherwise, the method returns to step 52.

[0107] Figure 6The steps of the method are shown when a wavelength-based method is selected.

[0108] The third step 54 then includes a first sub-step 54a that derives the representative wavelength of the adjusted color point information. This utilizes a conversion function 56 that maps xy values ​​to the dominant wavelength. Similarly, a conversion step from XYZ to xyY can be used if desired.

[0109] The representative wavelength is the dominant wavelength. For example, the dominant wavelength is defined in CIE color coordinates by drawing a line through the white point and the x, y coordinates. The wavelength at which the line intersects the boundary of the color space is the dominant wavelength. It has been found that color shift caused by electric current moves more or less parallel to the boundary in CIE space, so the dominant wavelength is a robust way to represent this color shift.

[0110] The second sub-step 54b involves adjusting the representative wavelength based on the latest current drive level of the corresponding illumination channel. This utilizes model 58, which shows the dependence of the dominant wavelength on the current, using the value dλ / dI.

[0111] The third sub-step 54c involves further adjusting the chromaticity information based on the already adjusted representative wavelength. This utilizes a transformation function 60 that maps the dominant wavelength back to xy values. This transformation function, for example, describes the chromaticity color coordinates x and y as functions of the dominant wavelength.

[0112] This method for modeling the dependence of color on drive current is particularly well-suited for direct LEDs. In this way, the method takes into account the different drive currents required for the dominant wavelength.

[0113] The same step 61 is used to convert back to XYZ coordinates.

[0114] Using the same fourth step 62, and the fourth step 62 again involves using further adjusted color point information to determine the flux contribution of each illumination channel to achieve the desired combined color point and combined light output flux from multiple illumination channels.

[0115] For each channel, to form this set of desired flux levels, the same fifth step 64 involves updating the current drive levels of multiple lighting channels to create updated current drive levels. These are the current levels required to achieve the defined flux contribution for each lighting channel. These current levels are fed back to step 54b.

[0116] The same sixth step 66 involves using a temperature-dependent model 68 to update the temperature estimate to create an updated temperature estimate.

[0117] In step 70, the same convergence test is performed to determine if the iterative process can be stopped. If convergence occurs, the method terminates in step 72; otherwise, the method returns to the second step.

[0118] Note that the light source can include both direct LEDs and phosphor-converted LEDs. Therefore, these two different correction models can be combined within a single system. However, either correction model can be used for either or both types of LEDs. However, wavelength correction methods will yield better results, particularly for direct LEDs.

[0119] Of course, other transformations can be used to give a simple relationship between temperature and current on one side and CIE 1936 XYZ coordinates on the other. For example, another method can use CIE 1976 coordinates and first describe the offsets as du′ / dT and dv′ / dT and / or du′ / dI and dv′ / dI.

[0120] The most suitable model can be found by fitting the measurement data to different coordinate systems and selecting the most appropriate one. Further improvements can be made by using nonlinear polynomial fitting, power fitting, exponential fitting, or logarithmic fitting.

[0121] Therefore, this method determines the current drive levels of a set of channels to achieve a desired color point and desired brightness (e.g., dimming level), but ensures that the effect of operating channels with different currents on the resulting color point is taken into account. Color point control and brightness level (i.e., dimming level) control are achieved, ensuring that the color point remains constant across all brightness (i.e., dimming) levels. This method considers the possibility that different color points in the illumination channels require different drive currents.

[0122] This method allows for altering the balance of different channels to achieve the desired setpoint of the complete light source. Color shifts with varying driving current are temperature-independent, and therefore are modeled as independent effects. In addition to temperature compensation, this method allows for the separate consideration of the nonlinear flux-current relationship explained above, as well as the color point variation with current.

[0123] Convergence tests, for example, involve determining whether the temperature estimate has converged such that the next update gives a change below a threshold. Similarly, convergence can (alternatively or otherwise) test whether the current drive level has converged such that the next update gives a change below a threshold.

[0124] Therefore, this method can iteratively obtain a set of correct color points (and output flux) based on accurate temperature estimation and by properly adapting the current drive level to compensate for the influence of the current drive level on the color points.

[0125] The above method is based on analog amplitude modulation. However, it can be combined with digital pulse width modulation in various ways, as described below.

[0126] In addition to PWM dimming systems, amplitude modulation can be used to improve resolution. Many standard PWM systems use only 8-bit dimming control. However, 8 bits of resolution is insufficient for deep dimming. By using amplitude modulation to change the total current, a gain in resolution can be achieved. For example, amplitude dimming from 100% to 12.5% ​​adds a precision gain equivalent to the 3 additional bits in a full PWM system.

[0127] One option is to use amplitude modulation dimming below a certain total system dimming level, so that initial dimming is performed using PWM dimming. However, this approach will exhibit the inherent flicker of PWM dimming systems when high brightness is present.

[0128] Another alternative is to use amplitude modulation to initiate system dimming. This initial amplitude modulation can be reduced, for example, to a dimming level of 20% to avoid a large current range and wide frequency band for fitting consistent LED behavior. Below 20%, additional dimming is then achieved using PWM control.

[0129] Therefore, there are three possible configurations that combine amplitude modulation and PWM dimming.

[0130] (i) First, dim the system using PWM dimming. Add amplitude modulation dimming to improve resolution at low light (i.e., low brightness) levels.

[0131] (ii) First, dim the system using amplitude modulation dimming to avoid flicker. Add PWM dimming to avoid an excessively large AM dimming range and reduce the risk of inaccurate model fitting.

[0132] (iii) Combine amplitude modulation and PWM dimming for all dimming levels. For example, this could involve dimming in a way that the maximum PWM duty cycle is always 1. In this way, PWM control sets the difference between channels but with the maximum duty cycle. Amplitude dimming then provides scaling. This is particularly attractive in parallel-switched multichannel systems.

[0133] Figure 7 This demonstrates how to obtain the relative flux contribution of each channel relative to the Y0 value of the LED channel, i.e., the channel's fractional value f_ch.

[0134] This method involves solving the vector equation shown, which relates the temperature and current corrected LED values ​​to the target XYZ value (X... T Y T Z T Mapping between )

[0135] This produces channel fractions f1 to fn. Therefore, the output is the relative flux fraction f1…fn for an n-channel system. The relative flux fraction indicates how much flux each channel should produce to meet the target flux. The system needs to ensure that the value of f is between 0 and 1. If f is greater than 1, the target on the right should be scaled.

[0136] Figure 8 One method is shown that enables PWM dimming to be reduced to a threshold brightness and then amplitude modulation is used, or enables amplitude modulation to be set to a threshold and then PWM dimming is used.

[0137] This method is used after the desired flux level is known according to the method described above (step 62).

[0138] Some values ​​will be defined so that it can be understood. Figure 8 .

[0139] After temperature correction, the color point and flux of the channel are defined as x0, y0, and Y0.

[0140] Therefore, Y0_ch is the temperature correction flux for a specific channel, as indicated at the end of step 54 in the flowchart.

[0141] x(It_ch) and y(It_ch) give the color point correction of the target current (It) for each channel (ch) after amplitude modulation dimming.

[0142] Yt_ch is the target flux (Yt) of the channel (ch) when PWM is set to 1 (i.e., when it is permanently on).

[0143] It_ch is the target current (It) of the channel (ch) after amplitude modulation dimming.

[0144] When the iteration is complete, Ych(It_ch) = Yt_ch. In other words, the flux of the channel at the target current is equal to the target flux.

[0145] Ych is a function that describes the nonlinear relationship between flux and current.

[0146] If amplitude modulation dimming should be used first, define a target value relFlux_lim. relFlux_lim gives the flux relative to Y0; below this flux, PWM dimming will be used.

[0147] If PWM dimming should be used first, define a target value PWM_lim. PWM_lim describes the lowest dimming level that is still possible when using PWM dimming.

[0148] In scenario (i) above (where the system is first dimmed using PWM dimming, and amplitude modulation dimming is added to improve resolution in low-light conditions), the target relFluxlim is used. When relFlux_lim = 0, pure amplitude modulation dimming exists, and there is no initial PWM dimming.

[0149] When PWM_lim < 1, the above scenario (ii) (firstly, amplitude modulation dimming is used to dim the system to avoid flicker, and PWM dimming is added to avoid excessive AM dimming range) uses the target PWM_lim. When PWM_lim = 1, there is a combined system of scenario (iii), where PWM dimming is always used.

[0150] To obtain the desired color point of the lighting system, each channel should provide f_ch*Y0_ch lumens, where f_ch*Y0_ch = PWM_ch*Yt_ch.

[0151] Yt-ch is the amount of flux that the channel should provide after AM dimming.

[0152] In a full AM dimming system, Yt_ch = f_ch * Y0_ch. In a PWM dimming system, Yt_ch = f_ch * Y_ch / PWN_ch. The nonlinear relationship Ych(Ich) is used to determine the current such that f_ch * Y0_ch = Ych(Ich).

[0153] The method begins at step 90.

[0154] In step 92, a choice is made between whether amplitude modulation or PWM dimming should be used first.

[0155] For the initial amplitude modulation dimming, the target relFlux_lim and channel fraction are input into step 94.

[0156] Step 94 sets a correction value for each channel: corr_ch = min(1, fch / relFlux_lim). This correction cannot be greater than 1.

[0157] This involves checking if the required lumens per channel are below the limit. If they are, a correction is applied. The limit is a value that is still accurate enough using color point correction with current.

[0158] Step 96 sets the target channel flux Yt_ch = Y0_ch x fch / corr_ch and sets the PWM value PWM_ch = corr_ch. The correction is the difference between the minimum allowed value and the calculated relative flux f_ch.

[0159] Therefore, the target flux is inversely proportional to corr_ch, and the PWM setting is proportional to corr_ch.

[0160] In step 98, the required current is then found for the new value Yt_ch. Therefore, the PWM and target current value have been found.

[0161] For the initial PWM dimming, the target PWM_lim and channel fraction are input into step 102. Step 102 sets a correction value corr_ch = max(1, PWM_lim / f_ch) for each channel. Therefore, the correction cannot be greater than 1.

[0162] Step 104 determines whether each channel needs to be calibrated.

[0163] This is a decision based on designer preference. The "yes" path provides a correction factor for each channel (and the ability in the driver to control the current individually for each channel). The "no" path uses only a single correction for all channels, and that single correction is the same for all channels.

[0164] If per-channel calibration is required, step 106 sets the target channel throughput Yt_ch = Y0_ch / corr_ch and PWM_ch = corr_ch.

[0165] Y0_ch is the flux of the channel at the nominal current. If a correction is applied to the PWM value (e.g., to make the channel fraction f_ch larger), the flux at 100% PWM needs to be reduced to Yt_ch.

[0166] f_ch is the flux fraction per channel. f_ch = flux(It_ch) / flux(Inom_ch)*PWM, where flux(It_ch) is the flux at PWM=1 and the target current It, and flux(Inom_ch) is the flux of the channel at the nominal current.

[0167] The target flux is inversely proportional to corr_ch, and the PWM setting is proportional to corr_ch.

[0168] If per-channel calibration is not required, step 108 sets the target channel throughput Yt_ch = Y0_ch / min(corr_ch) and PWM_ch = min(corr_ch).

[0169] In this case, all PWMs scale in a similar way, so the current will also scale in the same way (by first order).

[0170] In step 98, the required current is then found for the new value Yt_ch. Therefore, the PWM and target current value have been found.

[0171] Figure 8 A lighting system comprising multiple lighting channels 110 is shown, each channel including a light source with a different color point. A lighting controller 112 is part of a lighting driver 114 and uses the method described above to control the drive current to the different lighting channels.

[0172] The steps of the method (e.g., in) Figure 5 and Figure 6 (The Chinese text has already been numbered. However, this does not mean that no additional steps are involved.)

[0173] By studying the accompanying drawings, this disclosure, and the appended claims, those skilled in the art can understand and implement variations of the disclosed embodiments in practicing the claimed invention. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite articles "a" or "an" do not exclude a plural.

[0174] The fact that certain measures are listed only in mutually different dependent claims does not imply that a combination of these measures cannot be used for a beneficial purpose.

[0175] Computer programs may be stored / distributed on suitable media, such as optical or solid-state storage media provided with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunications systems.

[0176] If the term “adapted to” is used in the claims or specification, it should be noted that the term “adapted to” is intended to be equivalent to the term “configured to”.

[0177] No reference numerals in the claims should be construed as limiting the scope.

Claims

1. A method for controlling a lighting system, the lighting system comprising a plurality of lighting channels, the plurality of lighting channels comprising light sources having different color points, the method comprising: The first step (51) is to receive color point information, which includes nominal color point information about the light source; The second step (52) is to adjust the color point information based on the latest temperature estimate. The third step (54) further adjusts the color point information based on the current latest current drive level for the corresponding lighting channel, wherein the second and third steps can be performed in any order; In the fourth step (62), the further adjusted color point information is used to determine the flux contribution of each illumination channel to achieve the desired combined color point and combined light output flux from the plurality of illumination channels; Fifth step (64), update the current drive level for the plurality of lighting channels to create an updated current drive level to achieve the flux contribution of each lighting channel; The sixth step (66) is to update the temperature estimate based on the updated current drive level to create an updated temperature estimate; as well as Repeat steps 2 through 6 until (i) the temperature estimate converges to a value less than a threshold when it is updated, and / or (ii) the current drive level converges to a value less than a threshold when it is updated.

2. The method according to claim 1, comprising: Repeat steps 2 through 6 until (i) the temperature estimate converges to a value less than a threshold when it is updated, and (ii) the current drive level converges to a value less than a threshold when it is updated.

3. The method according to any one of claims 1 to 2, wherein the second step (52) comprises: Transform the CIE1936 XYZ color coordinates to CIE xyY chromaticity color coordinates, apply temperature correction to dx / dT, dy / dT, and flux, and then transform back to XYZ color coordinates.

4. The method according to any one of claims 1 to 2, wherein the third step comprises (54): using information related to the rate of change of CIExy chromaticity color coordinates relative to the driving current.

5. The method according to any one of claims 1 to 2, wherein the third step (54) comprises: The first sub-step (54a) derives a representative wavelength for the adjusted color point information; The second sub-step (54b) involves adjusting the representative wavelength based on the current latest current drive level for the corresponding illumination channel. as well as The third sub-step (54c) further adjusts the color point information based on the adjusted representative wavelength.

6. The method of claim 5, wherein the first sub-step (54a) uses a model (56) for converting from color points to representative wavelengths.

7. The method according to claim 6, wherein the second sub-step (54b) uses a current dependence model (58) for different wavelengths and determines the color point offset with wavelength based on the CIE x,y color coordinates as a function of the dominant wavelength model.

8. The method of claim 5, wherein the third sub-step (54c) uses a model (60) for converting from a representative wavelength to a color point.

9. The method according to any one of claims 1 to 2, further comprising: Pulse width modulation is applied to the drive current for the lighting channel.

10. A method for controlling a lighting system, the lighting system comprising a plurality of lighting channels, the plurality of lighting channels comprising light sources having different color points, the method comprising: For a first range of dimming levels, the method according to any one of claims 1 to 2 is applied; as well as For the second range of dimming levels, pulse width modulation dimming is applied.

11. The method of claim 10, wherein: The first range is for low brightness levels, and the second range is for high brightness levels; or The first range is for high brightness levels, and the second range is for low brightness levels.

12. A computer program product comprising computer program code, wherein when the computer program code is run on a computer, the computer program code is adapted to implement the method according to any one of claims 1 to 2.

13. A processor for controlling a lighting system, the lighting system comprising a plurality of lighting channels, the plurality of lighting channels comprising light sources having different color points, wherein the processor is programmed using a computer program product according to claim 12.

14. A lighting controller comprising the processor according to claim 13.

15. A lighting system comprising: Multiple lighting channels (110), each of which includes a light source with a different color point; as well as The lighting controller according to claim 14 is used to control the drive current to different lighting channels.

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