Lighting device comprising a light source and an optical reflector, and associated electronic device

Abstract

The invention relates to a lighting device (1) comprising a light source (100) and an optical reflector (200), the light source having a main direction of illumination which defines an optical axis (OA), the optical reflector comprising two segments, the first segment (210) comprising a first wall (211) which extends at least partially around the light source over a first height (H1) in the direction of the optical axis, the first wall being convergent in the direction of propagation of the light, the second segment (220) comprising a second reflective wall (221) and extending in the continuation of the first wall over a second height (H2) in the direction of the optical axis so as to reflect light rays coming from the light source, the second wall being divergent in the direction of propagation of the light. The invention also relates to an electronic device comprising such a lighting device.

Description

Description Title of the invention: Illumination device comprising a light source and an optical reflector, and associated electronic device Technical field

[0001] The present invention relates to the technical field of imaging, and in particular the illumination of a scene observed by an image sensor.

[0002] The invention relates more particularly to an illumination device comprising a light source and an optical reflector.

[0003] It also relates to an electronic device comprising an image capture unit and such an illumination device.

[0004] The invention finds a particularly advantageous application in the illumination of the passenger compartment of a motor vehicle for driver surveillance cameras. Technological background

[0005] Driver monitoring systems (DMS) are increasingly being used in the passenger compartment of motor vehicles. In this context, it is known to couple an image capture unit with an illumination device in order to maintain sufficient brightness regardless of the ambient light.

[0006] The images captured by these devices are then analyzed by image processing algorithms to extract the relevant information.

[0007] In order to improve the performance of image processing algorithms, the requirements for image quality are becoming increasingly high. One of the parameters used to improve the quality of captured images is the uniformity of scene illumination produced by the illumination device.

[0008] Traditionally, the light sources of lighting devices consist of one or more LEDs operating in the infrared range. LEDs generally have a Gaussian profile. The use of such light sources results in non-uniform illumination of the vehicle interior.

[0009] To increase the performance of current image processing algorithms, it is recommended that the scene illumination does not exceed a contrast of approximately 20% across the camera's field of view.

[0010] One solution to standardize the illumination of a light source is to add an optical component such as a diffuser.

[0011] However, this solution results in a significant loss of light intensity, leading to a loss of efficiency of the illumination device and a reduction in the quality of the captured images.

[0012] Another solution is to use a reflector surrounding the light source and allowing peripheral rays from the source and out of the field of view of the image capture unit to be reflected towards an area of ​​interest in the vehicle interior within the field of view of the image capture unit in such a way as to uniform the illumination.

[0013] This solution, although effective, leads to other sources of image degradation by redirecting stray light, in particular rays that are very inclined at the exit of the light source, to the image capture unit. Summary of the invention

[0014] In this context, an illumination device is provided comprising a light source and an optical reflector, the light source having a main illumination direction defining an optical axis and the optical reflector comprising two sections.

[0015] It is proposed here that the first section comprises a first wall extending at least partly around the light source over a first height in the direction of the optical axis, the first wall being convergent in the direction of propagation of the light.

[0016] This first wall, through its convergence, prevents stray light from propagating into the illumination device. Indeed, the rays emitted at the base of the light source and being very inclined can be reflected (specular or diffuse reflection) in the opposite direction to the propagation of the light.

[0017] The second section comprises a second reflective wall extending in the extension of the first wall over a second height in the direction of the optical axis so as to reflect light rays coming from the light source. The second wall is divergent in the direction of propagation of the light.

[0018] The second wall allows peripheral light from the light source to be reflected towards an area of ​​interest in the vehicle interior and thus creates uniform illumination.

[0019] According to one embodiment, the optical reflector comprises a third section comprising a third reflecting wall which extends over a third height in the direction of the optical axis, in the extension of the second wall of the second section.

[0020] Furthermore, the third wall of the third section may have a third angle of inclination relative to the optical axis less than 5°.

[0021] In one embodiment, the first wall and the second wall of the optical reflector each comprise at least one pair of two faces.

[0022] Further, the first wall and the second wall each comprise two pairs of two faces positioned such that the two faces of a pair face each other, on either side of the light source.

[0023] The faces of the sections can be flat.

[0024] In one embodiment, the wall of the first section of the optical reflector is reflective.

[0025] Preferably, the light source is an LED emitting in the infrared, and the walls of the sections are reflective in the infrared.

[0026] The invention also relates to an electronic device comprising an image capture unit and an illumination device as described above configured to illuminate the field of view of the image capture unit.

[0027] The various features, variations and embodiments of the invention may be combined with each other in various combinations to the extent that they are not incompatible or mutually exclusive. Brief description of the figures

[0028] In addition, various other characteristics of the invention emerge from the appended description given with reference to the drawings which illustrate non-limiting embodiments of the invention and where:

[0029] [Fig. 1] is a simulation of stray light within an electronic device as known from the prior art.

[0030] [Fig. 2] is a schematic sectional representation of the illumination device according to one embodiment of the invention,

[0031] [Fig. 3] is a schematic perspective representation of the illumination device of Figure 2,

[0032] [Fig. 4] is a schematic representation of an electronic device comprising the illumination device of Fig. 2,

[0033] [Fig. 5] is a schematic sectional representation of the illumination device according to an embodiment other than that of Figure 2,

[0034] [Fig. 6] is a simulation of the illumination generated by a conventional light source,

[0035] [Fig. 7] is a simulation of the illumination generated by the illumination device of Figure 2, and

[0036] [Fig. 8] is a graph representing the average and maximum illumination corresponding to the stray light at the camera input for the electronic device of Fig. 4 and for the electronic device of Fig. 1 as known from the prior art.

[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] A conventional electronic device 500 for monitoring the driver in the passenger compartment of a vehicle as known from the prior art is shown in FIG. 1. It comprises a conventional illumination device 520 as known from the prior art and an image capture unit 510. The conventional illumination device 520 comprises a light source 521 and a conventional optical reflector 522. Here the light source 521 is an infrared LED. The conventional optical reflector 522 is a continuous frustoconical reflective wall surrounding the light source 521.

[0039] The image capture unit 510 comprises a camera and is used to capture a scene illuminated by the conventional illumination device 520. The conventional electronic device 520 also comprises a protective glass 530. This protective glass may be made of glass or plastic.

[0040] Figure 1 shows stray light rays. Stray light rays include light rays that are emitted by the light source 521 and arrive at the image capture unit 510 without having illuminated the scene.

[0041] The majority of stray light rays are rays that are reflected inside the glass 530 of the conventional electronic device 500 to the image capture unit 510, without being able to exit the conventional electronic device 500.

[0042] The simulation of these rays shows that a large majority of these parasitic light rays are very inclined rays at the exit of the light source 521 and are reflected by the conventional optical reflector 522 in its portion closest to the light source.

[0043] This part of the illumination contributes little to the illumination of the scene, and therefore causes more loss of uniformity via stray rays than illumination contribution.

[0044] In Figure 2, an illumination device 1 according to an embodiment proposed by the invention is shown in section. It comprises a light source 100 and an optical reflector 200. This same illumination device 1 is shown in perspective in Figure 3.

[0045] The light source 100 may for example be an LED. The light source 100 defines an optical axis OA. The optical axis OA is the main direction of illumination of the light source, that is to say for example the direction in which the light intensity is maximum. The reflector may be oriented in such a way that its main axis coincides with the optical axis OA.

[0046] The optical reflector 200 here comprises a first section 210, a second section 220 and a third section 230.

[0047] The first section 210, closest to the light source 100, comprises a first wall 211. The first wall 211 comprises four faces surrounding the light source 100 and facing each other two by two.

[0048] The faces here are flat. They can be trapezoidal in shape.

[0049] The faces are inclined so that the surface defined by the first section 210 (in section orthogonal to the optical axis OA) decreases in the direction of propagation of the light. In other words, the faces converge towards the optical axis in the direction of propagation of the light. The faces may be symmetrical with respect to the optical axis OA.

[0050] A first inclination angle THETA1 is defined as the inclination angle of the faces of the first section 210 relative to the optical axis OA.

[0051] The faces are here reflective. In this way, the highly inclined rays coming from the light source 100, such as those creating stray light in the example of Figure 1, will be reflected in the opposite direction of the propagation of the light, towards the light source 100 itself. For example, the reflection here is specular.

[0052] Thus, when used with an image capture unit, as described below with reference to Figure 4, stray light will not exit the illumination device 1 and thus propagate to the image capture unit.

[0053] The faces are reflective at least in the wavelength range emitted by the light source 100 and / or in the wavelength range of the image capture unit. Here, the faces are reflective at least in the infrared.

[0054] Highly inclined rays are defined as rays forming an angle with the optical axis between an angle ALPHA1 and 90°. The angle ALPHA1 is the angle between the optical axis OA and the ray furthest from the optical axis OA not reflected by the first section 210.

[0055] In another embodiment, the reflection of light on the first section is a diffuse reflection.

[0056] Alternatively, the faces may be absorbent in the wavelength range emitted by the light source 100. In this case, the rays are absorbed and do not propagate to the image capture unit.

[0057] The second section 220 extends in continuity with the first section 210. The second section 220 comprises a second wall 221. The second wall 221 comprises four reflective faces which each extend in continuity with a corresponding face of the first section 210. The faces are arranged in two pairs. In each of the pairs, the faces are positioned opposite each other.

[0058] The faces here are flat. They can be trapezoidal in shape.

[0059] Unlike the first section 210, the faces are inclined so that the surface defined by the second section 220 (in section orthogonal to the optical axis OA) increases in the direction of propagation of the light. In other words, the faces diverge from the optical axis in the direction of propagation of the light.

[0060] A second inclination angle THETA2 is defined as the inclination angle of the faces of the second section 220 relative to the optical axis OA. The first inclination angle THETA1 and the second inclination angle THETA2 are of opposite signs.

[0061] This second section 220 reflects a portion of the rays coming from the light source 100 and forming an angle with the optical axis between ALPHA1 and an angle ALPHA2. The angle ALPHA2 is defined as the angle between the optical axis OA and the ray furthest from the optical axis OA not reflected by the second section.

[0062] The third section 230 extends in continuity with the second section 220. The third section 230 comprises a third wall 231. The third wall 231 of the third section 230 comprises four faces which each extend in continuity with a corresponding face of the second section 220. The faces are arranged in two pairs. In each of the pairs, the faces are positioned opposite each other.

[0063] The faces here are flat. They can be trapezoidal in shape.

[0064] A third inclination angle is defined as the inclination angle of the faces of the third section 230 relative to the optical axis OA.

[0065] This third section 230 reflects a portion of the rays coming from the light source 100 and forming an angle with the optical axis between ALPHA2 and an angle ALPHA3. The angle ALPHA3 is defined as the angle between the optical axis OA and the ray furthest from the optical axis OA not reflected by the third section 230.

[0066] For example, for a light source emitting a light emission cone forming an angle between 50° and 80° with the optical axis, the angle ALPHA1 may be between 55° and 65° and / or the angle ALPHA2 may be between 32° and 48° and / or the angle ALPHA3 may be between 25° and 40°.

[0067] The faces of the second section 220 and / or third section 230 are here reflective in the infrared.

[0068] The second section 220 and the third section 230 make it possible to create a more uniform illumination by reflecting the most inclined rays which are not in the field of view of the image capture unit towards areas of interest which lack illumination in the field of view of the image capture unit.

[0069] For example, in the case of a 100 Gaussian light source, which is the case of the LED here, the outermost rays will be reflected towards the peripheral areas of the central peak of illumination or the edges of the field of view of the image capture unit.

[0070] In Figure 2, several light rays are observed coming from the light source 100. The rays represented in solid lines have an inclination angle less than ALPHA3 and are not reflected. The light rays represented in dotted lines are reflected by the second section 220. The reflected rays represented with dashes are reflected by the third section 230. The rays represented with dashes and in dotted lines will thus make it possible to compensate for the Gaussian distribution of the LED by bringing luminous flux back into the edges of the field.

[0071] Furthermore, the optical reflector 200 can be produced by standard industrial processes such as injection molding followed by deposition of a reflective coating by physical vapor deposition (PVD) or galvanization.

[0072] In Figure 4, an electronic device 2 is shown according to one embodiment of the invention. The electronic device 2 comprises the illumination device 1 of Figures 2 and 3 and described previously. It also comprises an image capture unit 20 and a control unit 30 coupled to the illumination device 1 and to the image capture unit 20. The electronic device 2 can be placed in a motor vehicle, for example to form a driver monitoring system.

[0073] The image capture unit 20 makes it possible to capture images of an environment facing it, here a part of the passenger compartment of the motor vehicle. For example, the field of vision of the image capture unit 20 is directed towards the usual position of the driver. The image capture unit 20 can be a camera and capture the entire scene illuminated by the illumination device 1. The control unit 30 is configured to analyze the captured image.

[0074] The control unit may be designed to determine (when the driver is in his usual position) a level of unfitness to drive (e.g. a level of distraction or a level of drowsiness) by means of analysis of the captured image.

[0075] In order to avoid disturbing people near the electronic device and to standardize the use of image capture during the day and at night, the source light source 100 can operate in the infrared, light invisible to the human eye. The image capture unit 20 operates at least in the same wavelength range as the light source 100. Here, the image capture unit 20 operates only in the infrared. Alternatively, the image capture unit can operate in the infrared and visible.

[0076] To improve the performance of the analysis of the captured image, it is preferable that the uniformity of the illumination is such that the illumination contrast is less than 20%. This means that two points in the field of view of the image capture unit 20 must receive an illumination difference of less than 20%.

[0077] The inclination angles and heights of the faces of the sections were calculated by numerical simulation to meet this objective.

[0078] The first section 210 may have a first height H1 on the optical axis of between 1 and 1.5 mm. Here the first height H1 is 1.3 mm. The absolute value of the first inclination angle THETA1 of the first section 210 relative to the optical axis (OA) may be between 8 and 15°. Here the absolute value of the first inclination angle measures 10°.

[0079] The second section 220 may have a second height H2 on the optical axis of between 2 and 5 mm. Here the second height H2 is 3 mm. The absolute value of the second inclination angle THETA2 of the second section 220 relative to the optical axis (OA) may be between 8 and 15°. Here the absolute value of the second inclination angle measures 10°.

[0080] The third section 230 may have a third height H3 on the optical axis of between 0.8 and 1.5 mm. Here the third height H3 is 1 mm. The absolute value of the third angle of inclination of the third section 230 relative to the optical axis (OA) may be less than 5°. Here the absolute value of the third angle of inclination measures 1°.

[0081] For a better result on the uniformity of the source, the inclination of the faces of the third section 230 could be zero. However, in order to be able to more easily manufacture the optical reflector 200, which is generally molded, it is preferable that the faces of the third section 230 are slightly inclined.

[0082] These values ​​are dependent on the light source 100 and the configuration of the image capture unit 20. They are given here for informational purposes and are not limiting.

[0083] The electronic device 2 here comprises an outer casing 40 and a removable cover 42. The outer casing 40 makes it possible to mechanically hold the elements relative to each other. The removable cover 42 makes it possible to easily access the interior of the electronic device 2.

[0084] The electronic device 2 also comprises a printed circuit 50 on which the light source 100 and the control unit 30 are fixed. The optical reflector 200 is fixed here using fixing clips 41.

[0085] Alternatively, the illumination device 1 could be entirely attached directly to the printed circuit board 50.

[0086] In Figure 5, an illumination device 1 according to another embodiment of the invention is shown. The illumination device 1 here comprises a light source 100 and an optical reflector 200. The light source 100 may be a source with Gaussian illumination, such as for example an LED. The optical reflector 200 here comprises two sections.

[0087] The first section 210 comprises converging faces and makes it possible to limit the propagation of stray light. The second section 220 comprises diverging faces and makes it possible to standardize the illumination in the same manner as described previously.

[0088] Figure 6 represents a simulation 110 of the illumination generated by the light source 100 used in the illumination device 1. A Gaussian distribution of the light is observed.

[0089] Figure 7 represents a second simulation 120 of the illumination generated by the illumination device 1 of Figure 2. Thanks to the optical reflector 200, the peripheral light rays are folded around the light peak, thus generating uniform illumination over a wider field of view.

[0090] Figure 7 shows a zone 300 (usually called a “headbox”) corresponding to the possible location of the driver’s head. observes that the illumination simulated here is uniform over a field of view large enough to fully illuminate the aforementioned area 300.

[0091] Figure 8 represents a graph showing the average (Avg. Irrad) and maximum (Max. Irrad) irradiance due to stray light as a percentage relative to a standard value at camera input for the electronic device of Figure 4 (Inv. DMS) and for the conventional electronic device of Figure 1 comprising a conventional illumination device (Std. DMS).

[0092] It is observed that the stray light is lower when using the electronic device of Figure 4 and as defined herein than for the conventional electronic device of Figure 1 comprising a conventional illumination device.

Claims

Claims 1. Illumination device (1) comprising a light source (100) and an optical reflector (200), the light source (100) having a main illumination direction defining an optical axis (OA), the optical reflector (200) comprising two sections, the first section (210) comprising a first wall (211) extending at least partly around the light source (100) over a first height (H 1) in the direction of the optical axis (OA), the first wall (211) being convergent in the direction of propagation of the light, the second section (220) comprising a second reflective wall (221) and extending in the extension of the first wall (211) over a second height (H2) in the direction of the optical axis (OA) so as to reflect light rays coming from the light source, the second wall (221) being divergent in the direction of propagation of the light.

2. Illumination device (1) according to claim 1, in which the optical reflector (200) comprises a third section (230) comprising a third reflective wall (231) which extends over a third height (H3) in the direction of the optical axis, in the extension of the second wall of the second section.

3. Illumination device (1) according to claim 2, wherein the third wall (231) of the third section (230) has a third angle of inclination relative to the optical axis of less than 5°.

4. Illumination device (1) according to one of claims 1 to 3, wherein the first wall (211) and the second wall (221) of the optical reflector (200) each comprise at least one pair of two faces.

5. Illumination device (1) according to claim 4, wherein the first wall (211) and the second wall (221) each comprise two pairs of two faces positioned such that the two faces of a pair are opposite each other, on each side of the light source (100).

6. Illumination device (1) according to one of claims 4 or 5, in which the faces are flat.

7. Illumination device (1) according to one of claims 1 to 6, in which the first wall (211) of the first section (210) of the optical reflector (200) is reflective.

8. Illumination device (1) according to one of claims 1 to 7, in which the light source (100) is an LED emitting in the infrared, and in which the walls (211, 221) of the sections (210, 220) are reflective in the infrared.

9. Electronic device (2) comprising an image capture unit (20) and an illumination device (1) according to one of the preceding claims configured to illuminate the field of view of the image capture unit (20).

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