LIGHTING DEVICE AND IMAGE DEVICE WITH SUCH A LIGHTING DEVICE

Description

technical field

[0001] The present invention relates to the technical field of imaging, and in particular to image capture using an illuminator.

[0002] The invention relates particularly to an illumination device and an imaging device comprising such a device, for example but not limited to image capture in the passenger compartment of a motor vehicle. Technological background

[0003] The term imager is understood here as any device capable of capturing images which are either two-dimensional images, such as photos or videos, or three-dimensional images such as those captured by an imager implementing time of flight measurement techniques.

[0004] It is known to couple an imager to an illumination device in order to maintain sufficient brightness regardless of ambient brightness, or to generate light pulses necessary for the implementation of time-of-flight measurement techniques.

[0005] To avoid disturbing people near the imager, infrared light sources, which emit beams invisible to the human eye, are commonly used. However, infrared sources can pose a risk to the human eye under certain conditions, particularly when their intensity becomes too high, especially since they do not trigger a protective reflex in people exposed to infrared illumination.

[0006] Typically, light sources in imaging illumination devices, particularly infrared light sources, are coupled to a diffuser that serves the dual purpose of increasing the angular spread and reducing the luminous intensity of the light beam emitted by the source and passing through the diffuser. Therefore, in illumination devices, the light source must be configured to generate a high-intensity beam in order to maintain sufficient luminous intensity downstream of the diffuser relative to the beam propagation direction.

[0007] A risk to the human eye arises when the diffuser is faulty, for example absent or broken.

[0008] Existing solutions to address the risk of diffuser failure include securely fixing the diffuser, for example using a dedicated frame, protecting it with a housing, and / or using a diffuser presence detector to cut off the light source if the diffuser is not detected.

[0009] However, these solutions do not prevent certain types of damage to the diffuser, such as thermal damage, for example exposure to very high heat, which can alter its internal structure and therefore its functions of diffusion and reduction of light intensity without altering its external structure.

[0010] Furthermore, such solutions require the use of bulky means, which goes against the current trend of miniaturizing imaging devices.

[0011] Therefore, there is a need for a lighting device that is compact and safe for the human eye.

[0012] US2017 / 0307164 A1 discloses an integrated lighting device within a motor vehicle. EP3258746 A2 discloses the securing of a light module including a laser source. Summary of the invention

[0013] According to one aspect, an illumination device is proposed comprising an illumination module including an optical output configured to emit a light beam having an angular spread, the illumination module including a light source and an optical diffuser, the light source being configured to generate said light beam, the optical diffuser being arranged to receive the light beam and to diffuse it towards the optical output so that the angular spread has, downstream of the diffuser with respect to the direction of propagation of the light beam, a downstream value greater than an upstream value of the angular spread upstream of the diffuser.

[0014] According to a general characteristic of this aspect, the device includes a control module configured to emit a control signal with an alarm value when the value of the angular spread of the light beam emitted by the optical output falls below a first predetermined threshold, the control module comprising a photoreceptor optically coupled to the optical output and configured to measure a light intensity, the control module being configured to deliver the control signal with the alarm value when the value of the light intensity is less than or equal to a second predetermined threshold, the device further comprising a control circuit configured to deactivate the light source upon receipt of the control signal with the alarm value.

[0015] The angular spread of a light beam is understood here and in the rest of the description as the angle of divergence of the beam with respect to its axis of propagation, that is to say here with respect to a direction normal to the diffuser.

[0016] Thus, by detecting a decrease in the angular spread of the light beam exiting the diffuser, a consequence of diffuser failure is detected, regardless of the cause. Failure detection is therefore reliable, and the device is thus safer than those of the prior art.

[0017] According to the invention, the control module includes a waveguide which has a propagation direction transverse to the beam and which is configured to optically couple the optical output and the photoreceptor.

[0018] Thus, a smaller angular spread results in a smaller angle of incidence of the rays on the waveguide walls, and therefore a higher number of reflections within the waveguide. Consequently, losses in the waveguide due to successive reflections are greater, and the light intensity at the optical input is lower. This makes it possible to easily and reliably detect a diffuser failure. Furthermore, using a waveguide allows a portion of the control module to be kept away from the light beam, thus preventing excessive beam obstruction by the control module.

[0019] According to the invention, the device comprises a protective glass panel configured to allow the light beam to pass through it, the waveguide including at least a portion of the protective glass panel. The waveguide, for example, comprises two opposing, partially reflective walls of the protective glass panel. It should be noted that a failure of said portion of the protective glass panel is detectable by the device.

[0020] This eliminates the need for a separate waveguide and protective glass. The device is therefore significantly more compact. Furthermore, eliminating the need for a separate waveguide prevents additional beam obstruction by the waveguide.

[0021] The control circuit can be configured to deliver a control pulse signal having either a first state or a second state, the light source being configured to generate the light beam when the control pulse signal is in the first state and to be deactivated when the control pulse signal is in the second state.

[0022] Pulsed control of the light source is particularly suitable for implementing time-of-flight measurement techniques.

[0023] The photoreceptor may include a signal terminal configured to deliver a measurement signal representative of the light intensity, the control module including a comparator comprising a first comparator input electrically coupled to the signal terminal, a second comparator input configured to receive a reference signal whose value is representative of the second threshold and a comparator output configured to deliver the control signal having the alarm value if the value of the signal on the first comparator input is less than or equal to the value of the signal on the second comparator input.

[0024] The signal terminal can be coupled to the first comparator input via a memory circuit configured to maintain the value of the measurement signal between two successive presentations of the first state of the control pulse signal.

[0025] Therefore, the values ​​of the measurement signal are excluded from detection when the light source is not generating the beam. This results in more precise detection and a more reliable device.

[0026] The signal terminal can be coupled to the first comparator input via a subtractor configured to deliver to the first comparator input a differential signal whose value is equal to the difference between the value of the measurement signal when the control pulse signal is in the first state and the value of the measurement signal when the control pulse signal is in the second state.

[0027] A temporal filtering operation is therefore performed, advantageously excluding from detection the signal components representative of ambient light. The device is thus more reliable.

[0028] A bandpass filter can be interposed between the photoreceptor and the optical output.

[0029] An optical bandpass filter is a simple way to achieve filtering and make the device more reliable.

[0030] The control module may include at least one opaque insulating partition protecting it from ambient light.

[0031] The light source may include at least one vertical cavity laser diode emitting from the surface.

[0032] Vertical cavity surface emitting laser diodes (commonly referred to by those skilled in the art under the English acronym VCSEL, for "Vertical Cavity Surface Emitting Laser") exhibit very low temperature drift and allow the generation of a beam in a very narrow wavelength band which, especially when the control module includes a narrow bandpass filter, allows good immunity to ambient light.

[0033] In addition, the ability of VCSEL diodes to generate short pulses makes it possible to increase the peak power of the pulses and therefore to increase the signal-to-noise ratio, which is particularly advantageous for the implementation of time-of-flight methods.

[0034] According to another aspect, an imaging system is proposed comprising an image capture device and an illumination device according to the invention.

[0035] The different features, variants and embodiments of the invention can be combined with each other in various ways insofar as they are not incompatible or mutually exclusive. Brief description of the figures

[0036] Furthermore, various other features of the invention become apparent from the attached description made with reference to the drawings which illustrate non-limiting embodiments of the invention and where: [ Fig. 1] there figure 1 is a schematic representation from a structural point of view of an illumination device according to an embodiment of the invention, [ Fig. 2 ] there figure 2 is a schematic representation of the lighting system of the figure 1 in which the diffuser of the lighting module is faulty, [ Fig. 3 ] there figure 3 is a schematic representation from a structural point of view of the illumination device according to an example of a control module without a waveguide, [ Fig. 4 ] there figure 4 is a schematic representation from a structural point of view of an imaging system according to an embodiment of the invention, [ Fig. 5 ] there figure 5 is a schematic representation from a structural point of view of another embodiment of the lighting device according to the invention in which the control module is protected by an opaque partition, [ Fig. 6 ] there figure 6is a schematic representation from a structural point of view of another embodiment of the illumination device according to the invention in which the control module includes an optical bandpass filter, [ Fig. 7 ] there figure 7 is a schematic representation from an electrical point of view of the lighting device according to the invention, and [ Fig. 8 ] there figure 8 is a schematic representation from an electrical point of view of the lighting device according to an embodiment of the invention

[0037] It should be noted that in these figures the structural and / or functional elements common to the different variants may have the same references. Detailed description

[0038] An illumination device according to the invention, as schematically represented on the figure 1and designated as a whole by reference 1, comprises an illumination module 2, a control module 3 optically coupled to the illumination module and a control circuit 4 electrically coupled to the illumination module 2 and the control module 3.

[0039] The illumination module 2 includes an optical output 22 configured to deliver a light beam 5, a light source 20 and a diffuser 21. The light source 20 is configured to generate the light beam 5 and the diffuser 21 is arranged to receive it and deliver it to the optical output 22. These elements of the illumination module 2 are in this example housed in a BT enclosure.

[0040] Here, the BT housing has an opening in which the diffuser 21 is housed. Thus, the optical output 22 is formed by one face of the diffuser 21. Alternatively, the diffuser could be positioned upstream of the optical output relative to the direction of propagation of the beam 5. In this case, the opening of the BT housing would act as the optical output.

[0041] The diffuser 21 is configured to increase the angular spread of the beam and reduce its intensity. Thus, upstream of the diffuser relative to the propagation direction of beam 5, beam 5 has an angular spread with an upstream value θ1 of 10°. Downstream of the diffuser, the beam 5 has an angular spread with a downstream value θ2 greater than the upstream value θ1, the downstream value θ2 being 50°.

[0042] The light source 20 is presented here in the form of a matrix of light-emitting diodes (LEDs) mounted on a printed circuit board. The LEDs are VCSELs configured to generate the beam 5 in a spectral band between 800 nanometers and 1000 nanometers.

[0043] The control module 3 is configured here to transmit a CTRL control signal to the control circuit. This signal can have either a neutral value, for example, a low state, or an alarm value, for example, a high state. The control module is designed to detect an abnormal decrease in the angular spread of the light beam 5, i.e., a drop below a predetermined threshold for the angular spread value. If such a decrease is detected, the control module 3 generates the CTRL control signal with the alarm value; otherwise, it generates the CTRL control signal with the neutral value.

[0044] To this end, the control module 3 includes a photoreceptor 30 optically coupled to the optical output 22 and configured to measure light intensity. The control module 3 is configured to generate the control signal with the alarm value when the light intensity measured by the photoreceptor 30 crosses a second predetermined threshold. Here, the value of the second predetermined light intensity threshold is representative of the value of the first predetermined angular spread threshold; that is, it is directly related to this value, as will be seen below.

[0045] In this embodiment, the photoreceptor 30 is optically coupled to the optical output 22 via a waveguide 6 having a propagation direction DP transverse to the light beam 5, and in particular in this example a propagation direction DP orthogonal to the propagation direction DF of the beam 5. A first opaque partition CL1 is located here between the photoreceptor 30 and the illumination module 2 so that the photoreceptor 30 is optically coupled to the illumination module 2 via the waveguide 6 only.

[0046] Here, the waveguide 6 is formed by a protective glass located downstream of the illumination module 2 (on the path of the light beam 5) so as to be crossed by the beam 5. The protective glass also extends above the photoreceptor 30 so that the illumination module 2 and the photoreceptor 30 are located on the same side of the protective glass and are protected by the protective glass.

[0047] The waveguide 6 is formed by a first partially reflective wall 60 and by a second partially reflective wall 61 which delimit the protective glass 6. Part of the rays of the beam 5 which does not pass through the partially reflective walls 60 and 61 is reflected successively on the walls 60 and 61 so as to propagate along the direction of propagation DP.

[0048] As an example, the path of a first peripheral ray 50 of the beam 5 located at the periphery of the beam 5 is shown. The first peripheral ray 50 is guided from the optical output 22 to the photoreceptor 30 through the waveguide 6. The first peripheral ray 50 therefore passes twice through the first partially reflective wall 60 but never completely passes through the second partially reflective wall 61.

[0049] It should be noted here that since walls 60 and 61 are partially reflective, each reflection against either wall results in optical losses through the corresponding wall, and conversely each crossing of the wall results in optical losses by reflection.

[0050] And, since the first peripheral ray 50 is located at the edge of the beam 5, it has a maximum divergence angle with respect to the direction of propagation of the beam 5, and therefore a maximum angle of incidence on the partially reflective walls 60 and 61. Thus, for a given distance traveled in the waveguide 6, the first peripheral ray 50 will undergo fewer reflections than a light ray having a smaller divergence angle with respect to the direction of propagation of the beam 5. Here, the first peripheral ray 50 undergoes three reflections, only one of which is on the first peripheral wall 60.

[0051] Each reflection on the partially reflective walls 60 and 61 causes optical losses through said walls, the luminous intensity measured by the photoreceptor 30 is proportional to the number of reflections undergone by the peripheral beam 50, and therefore to the angular spread of the beam 5. Thus, the smaller the angular spread of the beam 5, the smaller the luminous intensity measured by the photoreceptor 30 will be.

[0052] Thus, as mentioned above, the measured light intensity value is representative of the angular spread value, and the value of the second predetermined light intensity threshold is representative of the first predetermined angular spread threshold.

[0053] Here, control module 3 is configured to generate the CTRL control signal showing the alarm value when the light intensity value is below the second predetermined threshold.

[0054] Control circuit 4 is configured to deactivate the light source upon receiving the CTRL control signal containing the alarm value. For example, control circuit 4 can be configured to disconnect the light source 20 from its power supply, as will be shown below.

[0055] There figure 2 This illustrates a configuration of device 1 in which the diffuser 21 is faulty, here absent. The angular spread therefore exhibits the upstream value even at the optical output 22.

[0056] The path of a second peripheral ray 51 originating from the edge of the beam 5, which has the upstream angular spread value, is shown. The ray is reflected off the partially reflective surfaces 60 and 61 at a lower angle of incidence and therefore undergoes a greater number of reflections, here 19, resulting in higher optical losses. Consequently, the second peripheral ray 50 reaches the photoreceptor 30 with a light intensity lower than the second predetermined threshold. The control module therefore transmits the CTRL control signal, which contains the alarm value, to the control circuit 4, which then deactivates the light source 20.

[0057] The device described here in connection with the figures 1 and 2The design includes a light source comprising a VCSEL diode array. However, this example of a light source embodiment is not limiting, and the light source could be different. In particular, the light source may consist of only a single diode. The light source may also be of a different nature, for example, comprising one or more laser sources that are not of the VCSEL type, such as edge-emitting laser diodes (EDDs), Fabry-Perot laser diodes, distributed feedback lasers (DFBs), or one or more light sources that are not light-emitting diodes (LEDs), such as incandescent lamps, discharge lamps, or fluorescent tubes.

[0058] In particular, the light source can be configured to deliver a light beam with a different upstream value than that mentioned above. For example, the upstream value of the angular spread can be between 1° and 20°.

[0059] The downstream angular spread value, which depends on the diffuser configuration and the upstream angular spread value, can be between 30° and 100°.

[0060] The device described above includes a waveguide formed by a partially transparent protective glass, which advantageously reduces the device's size. However, alternative embodiments not covered by the invention, which include a waveguide separate from the protective glass, such as an optical fiber, are conceivable. In particular, alternative embodiments of the device not covered by the invention are devoid of protective glass.

[0061] There figure 3 illustrates an alternative embodiment not covered by the invention in which the control module 3 does not have a waveguide, and in which the photoreceptor 30 is directly optically coupled to the optical output 22. Here, the photoreceptor 30 is placed at the periphery of the beam 5.

[0062] Thus, if the angular spread decreases, i.e., if the diffuser 21 fails, the photoreceptor 30 is no longer illuminated by the beam 5 with the upstream divergence value, and the light intensity it receives falls below the second threshold. The control circuit 4 then deactivates the light source.

[0063] The device according to this embodiment includes a protective glass 65 which does not act as a waveguide but simply serves to protect the device 1.

[0064] An imaging system according to the invention is illustrated by the figure 4and designated as a whole by reference numeral 7. The imaging system 7 here comprises an image capture device 70, here a camera held by a chassis 71, and an illumination device 1 as described previously in connection with the figures 1 and 2 The illumination device 1 is configured to illuminate a scene to be captured, for example, the interior of a vehicle, and the camera 70 is configured to capture the illuminated scene. For example, the images captured by the camera 70 are processed by an image processing circuit (not shown) for driver assistance purposes.

[0065] Alternatively, the imaging device 7 may include, as an imaging device, a three-dimensional image capture system and the illumination device is then configured to emit the light beam in a pulsed manner, in order to capture a three-dimensional image in particular by implementing time-of-flight measurement techniques.

[0066] There figure 5 illustrates a variant embodiment of the invention in which the illumination device described above is linked to the figures 1 and 2 It also includes a second opaque partition CL2 protecting the control module 3 from ambient light. The second opaque partition CL2 is positioned on a portion of the protective glass opposite the photoreceptor 30.

[0067] For example, the first opaque partition CL1 and the second opaque partition CL2 here form the walls of a box which isolates the photoreceptor 30 from ambient light and which has an opening 36 through which the protective glass passes, i.e. the waveguide 6.

[0068] According to an alternative embodiment illustrated by the figure 6A bandpass filter 37 is interposed between the photoreceptor 30 and the optical output 22. Here, the bandpass filter 37 is configured to allow light rays with wavelengths within the emission spectrum of the light source to pass through, taking into account all variations related to this source (manufacturing tolerances, temperature variations, variations in the angle of incidence), and to reflect or absorb light rays outside this range. In this example, the bandpass filter 37, combined with the light source 20 (a VCSEL laser), is configured to allow light rays to pass through in a band from 50 nm to 20 nm around the central wavelength of the VCSEL. The bandpass filter 37 is made up of a series of thin layers of materials with varying refractive indices on a glass substrate.

[0069] There figure 7illustrates schematically and from an electrical point of view the device 1 according to the invention, and particularly the illumination module 2, the control module 3 and the control circuit 4.

[0070] The light source 20 is here symbolically represented by a light-emitting diode coupled between a supply terminal BV configured to receive a supply voltage, for example here a voltage of a few volts, and a reference terminal GND, for example here ground.

[0071] The photoreceptor 30 is here symbolically represented by a photodiode whose cathode is coupled to the supply terminal BV and whose anode forms a signal terminal BS configured to deliver a measurement signal SM representative of the light intensity measured by the photoreceptor 30. A protection resistor Rp is coupled between the anode and the cathode of the photodiode 30.

[0072] The control module 3 further includes a comparator 32 having a first comparator input EC1, a second comparator input EC2, and a comparator output SC configured to deliver the CTRL control signal.

[0073] The signal terminal BS is connected to the first comparator input EC1 via a first memory circuit 33. This first memory circuit is an RC circuit comprising a first resistor R1, connected between the signal terminal BS and the first comparator input EC1, and a first capacitor C1, connected between the first comparator input EC1 and the reference terminal GND. Those skilled in the art will choose the values ​​of resistor R1 and capacitor C1 to form a low-pass filter suitable for the modulation or activation frequency of the illuminator. For example, for a TOF (Time Of Flight) sensor modulation at 25 MHz, a cutoff frequency of 5 MHz would be chosen. This is to prevent the SC output of comparator 32 from changing state with each light pulse.

[0074] The second comparator input is configured to receive an SRF reference signal representative of the value of the second predetermined threshold, and comparator 32 is configured to deliver the CTRL control signal with the neutral value when the value of the signal on the first comparator input EC1 is greater than the value of the SRF reference signal, and to deliver the CTRL control signal with the alarm value when the value of the signal on the first comparator input EC1 is less than or equal to the value of the SRF reference signal.

[0075] The control circuit 4 is configured to generate a CMD control signal having either a first state, here a high state (for example a few volts), or a second state, for example here a low state corresponding to a value of 0 volts.

[0076] The light source 20 is connected to the reference terminal GND via a first switch INT1, which is voltage-controlled by the control signal CMD. The first switch INT1 is configured to be closed when the control signal CMD is in its first state and open when the control signal CMD is in its second state. Thus, the power supply to the light source 20, and therefore the emission of the light beam 5, is controlled by the control signal CMD.

[0077] The signal terminal BS is coupled to the first memory circuit 33 via a second voltage-controlled switch INT2, configured to be closed when the control signal CMD is in its first state and open when the control signal is in its second state. Thus, the control circuit 4 is configured to disable photodetection when the light source 20 is not emitting the light beam 5.

[0078] In the illustrated embodiment, the CMD control signal is a pulsed signal, for example with a duty cycle of 50%. The light beam 5 is therefore emitted in a pulsed manner, and the illumination device 1 is particularly suitable for image capture using the time-of-flight method.

[0079] The memory circuit 33 is configured to maintain the value of the measurement signal SM between two successive high-state presentations of the control signal CMD. In this example, the time constant of the first RC circuit of the first memory circuit 33 is at least 5 times the period of the CMD pulse signal, and the maintenance of the measurement signal value SM is ensured with a tolerance of less than 1%.

[0080] The control circuit 4 is configured to deliver the CMD control signal presenting the second state continuously when the control signal presents the alarm value.

[0081] There figure 8 illustrates a variant implementation of the device as described previously in connection with the figure 7 , in which the control module further comprises a subtractor 34 and a second memory circuit 35.

[0082] The subtractor has a first subtractor input ES1, a second subtractor input ES2 and a subtractor output SS configured to deliver a differential signal whose value is equal to the difference between the value of the signal on the first subtractor input ES1 and the value of the signal on the second subtractor input ES2.

[0083] The first subtractor input ES1 is coupled to the signal terminal BS via the second memory circuit 35. The second memory circuit 35 includes a second RC circuit with a second resistor R2 connected between the signal terminal BS and the first subtractor input ES1, and a second capacitor C2 connected between the first subtractor input ES1 and the reference terminal GND. Those skilled in the art will choose the values ​​of resistor R2 and capacitor C2 to form a low-pass filter with respect to the modulation or activation frequency of the illuminator, in the same way as for resistor R1 and capacitor C1. For example, for a 25 MHz TOF sensor modulation, a cutoff frequency of 5 MHz would be chosen.

[0084] The BS signal terminal is coupled to the second memory circuit 35 via a third voltage-controlled switch INT3 configured to be open when the CMD control signal is in its first state and closed when the CMD control signal is in its second state. For example, here, the third switch INT3 is configured to receive the control signal via an inverter gate INV.

[0085] Thus the SS subtractor output is configured to deliver to the first comparator input a differential signal whose value is equal to the difference between the value of the measurement signal when the control pulse signal is in the first state and the value of the measurement signal when the control pulse signal is in the second state, i.e. a signal in which the component representing ambient light has been eliminated.

[0086] Various other modifications may be made to the invention within the scope of the appended claims. For example, although the embodiments of the figures 7 and 8 Although illustrated by analog circuits, the invention is perfectly compatible with digital technologies, for example involving integrated electronic circuits.

Claims

1. Lighting device comprising a lighting module (2) comprising an optical output (22) configured to emit a light beam (5) having an angular spread, the module (2) comprising a light source (20) and an optical diffuser (21), the light source (20) being configured to generate said light beam (5), the optical diffuser (21) being arranged to receive the light beam (5) and to diffuse it toward the optical output (22) so that the angular spread has, downstream of the diffuser (21) relative to the direction of propagation of the light beam (5), a downstream value (θ2) that is greater than an upstream value (θ1) of the angular spread upstream of the diffuser, the device (1) comprising a control module (3) configured to transmit a control signal (CTRL) having an alarm value when the value of the angular spread of the light beam emitted by the optical output (22) falls below a first predetermined threshold, the control module comprising a photoreceptor (30) optically coupled to the optical output (22) and configured to measure a light intensity, the control module being configured to deliver the control signal (CTRL) having the alarm value when the value of the light intensity is less than or equal to a second predetermined threshold, the device (1) further comprising a control circuit (4) configured to deactivate the light source upon receiving the control signal (CTRL) having the alarm value, the control module (3) comprising a waveguide (6) that has a direction of propagation (DP) transverse to the beam (5) and that is configured to optically couple the optical output (22) and the photoreceptor (30), the device being characterized in that it comprises a protective window configured to be traversed by the light beam, the waveguide (6) comprising at least one portion of the protective window.

2. Device according to Claim 1, wherein the control circuit (4) is configured to deliver a control pulse signal (CMD) having either a first state or a second state, with the light source (20) being configured to generate the light beam (5) when the control pulse signal (CMD) assumes the first state and to be deactivated when the control pulse signal assumes the second state.

3. Device according to Claim 2, wherein the photoreceptor (30) comprises a signal terminal (BS) configured to deliver a measurement signal (SM) representing the light intensity, the control module (3) comprising a comparator (32) comprising a first comparator input (EC1) electrically coupled to the signal terminal (BS), a second comparator input (EC2) configured to receive a reference signal (SRF), the value of which represents the second threshold and a comparator output (SC) configured to deliver the control signal (CTRL) having the alarm value if the value of the signal on the first comparator input (EC1) is less than or equal to the value of the signal on the second comparator input (EC2).

4. Device according to Claim 3, wherein the signal terminal (BS) is coupled to the first comparator input (EC1) by means of a memory circuit (33) configured to maintain the value of the measurement signal (SM) between two successive presentations of the first state of the control pulse signal (CMD).

5. Device according to Claim 3 or 4, wherein the signal terminal (BS) is coupled to the first comparator input (EC1) by means of a subtractor configured to deliver a differential signal to the first comparator input (EC1), with the value of the differential signal being equal to the difference between the value of the measurement signal (SM) when the control pulse signal (CMD) assumes the first state and the value of the measurement signal (SM) when the control pulse signal (CMD) assumes the second state.

6. Device according to any one of the preceding claims, wherein an optical bandpass filter (37) is interposed between the photoreceptor (30) and the optical output (22).

7. Device according to any one of the preceding claims, wherein the control module (3) comprises at least one opaque isolating partition (CL1, CL2) protecting it from ambient light.

8. Device according to any one of the preceding claims, wherein the light source (20) comprises at least one vertical cavity surface emitting laser diode.

9. Imaging system comprising an image capture device (70) and a lighting device (1) according to any one of Claims 1 to 8.