Lighting device designed to reduce glare using light-emitting diodes

Abstract

The invention relates to a lighting device for glare control comprising one or more lensless light-emitting diodes connected to a multi-lens optical system, including a Fresnel lens, enabling the production of substantially uniform illumination at a distance. [Fig 2] to be published with the abstract.

Description

Title of the invention: Lighting device for glare reduction using light-emitting diodes

[0001] The present invention relates generally to the field of lighting, in particular to lighting which must meet particular specifications, in particular capable of producing concentrated illumination over an area a few meters away, and has as its object a lighting device with light-emitting diodes (generally designated as LEDs) whose luminous flux is expressed in lumens.

[0002] In certain fields or applications, it is necessary to have lighting that meets certain technical, or even regulatory, specifications, for example in terms of intensity or uniformity of lighting at the level of the area to be illuminated.

[0003] This is particularly the case for lighting intended for military or police operations for the purpose of detecting or dazzling threats. In close combat or during hostile demonstrations, it is essential to enable an operator on foot to illuminate a forward area close to them with sufficient power. In a specific operating mode, a so-called threat zone of 1 square meter at a distance of 5 meters would be most suitable. In a specific operating mode for police officers operating during demonstrations, the lighting device is mounted on a shield held on the operator's arm. In such a use, the size and weight of the lighting device must be minimal.

[0004] Devices of the aforementioned type, which are currently commercially available, generally use standard white LEDs as their light source(s). The emitting area, usually referred to as the chip, is a square measuring 1 to 2 mm on each side. Each of these LEDs is typically paired with a collimator, such as those marketed by Gaggione, which reduces the divergence angle of the LED's beam. The maximum luminous power of these LEDs is limited, depending on the model, to between 150 and 300 lumens. These devices are marketed, for example, by Extrême Vision.

[0005] To obtain a sufficient dazzling effect, under the aforementioned conditions, the various physiological studies show that an eye illumination greater than 10000 lux (1 lux is equal to 1 lumen per square meter) is necessary.

[0006] To obtain such illumination with a small and lightweight lighting device, the luminance, denoted L0, expressed in candelas per square meter, of the LED chip is a determining factor. The luminance L1 of the radiation The luminance emitted by the lighting device is slightly less than LO, the attenuation being caused by the transmission coefficient of the optical elements composing the device. Since the illumination of the threat zone is always proportional to Ll, it is thus shown that, for an optical device of a given size, the luminance LO is one of the main factors of efficiency. LEDs such as the Osram Ostar LECG models, which can emit a luminous flux of 8000 lumens, make it possible to achieve a luminance of 400 million candelas per square meter, or more than 8 times the luminance of a typical white LED. LEDs such as the LECGP2 or LECGP3 models do not have attached lenses and require a dedicated optical system, which is claimed in this invention.

[0007] In a non-exhaustive operating mode, the device uses LECGP2 LEDs whose spectrum has a maximum emission near 550 nm, which is the wavelength to which the eye is most sensitive. Figure 1 shows on the same graph the spectrum of an LED such as the LECGP2 model (1) and the function V(1) (2) which characterizes the eye's sensitivity as a function of wavelength 1. These two spectra are substantially superimposed and thus allow for good luminous efficacy.

[0008] Many LEDs are fitted with a lens made of plastic or silicone material attached to the LED, which fits into collimators as described above and is used in state-of-the-art devices for glare control. High-power LEDs such as the Osram LECGP2 or LECGP3, as described above, do not have these lenses and consequently produce a Lambertian emission pattern with perfectly constant luminance over a half-space.

[0009] The object of the present invention is the design of an optical system adapted to the aforementioned types of LEDs, enabling the efficient collection of such Lambertian radiation in order to illuminate the threat area in a substantially uniform manner.

[0010] On the other hand, given that the use of this device is carried out by an external operator most often on foot, the LEDs are controlled by an electrical supply powered by a rechargeable battery.

[0011] To perform efficient collection of the LED's luminous flux, the optical device has at least two lenses made of transparent material, a first lens advantageously plano-convex, having its face substantially flat in relation to the LED at a distance close to the LED, its convex face being able to be aspherical, and, a second lens which is advantageously a so-called Fresnel lens.

[0012] The first lens is made of transparent material which can be glass or plastic, its position is close to the LED, the distance between the LED and the first lens always being less than the thickness of the lens at its center.

[0013] The second lens is advantageously a Fresnel lens, which can be made of glass or plastic, and whose focal length and position allow the width of the illuminated area to be modified at a given distance. The advantage of using a Fresnel lens compared to a conventional lens of the same focal length is the reduction in weight and size. This is particularly advantageous for use by a person on foot.

[0014] Thus, according to the invention, the lighting device intended for glare comprises a light-emitting diode or LED without an attached lens, driven by an electronic circuit powered by a rechargeable battery and associated with an optical system capable of recovering the luminous flux emitted by said LED and producing at a distance a substantially uniform illumination, said optical system comprising at least two lenses made of transparent material, characterized in that the optical system comprises a first lens whose distance to the surface of the LED is less than the central thickness of said first lens and a second lens which is a so-called Fresnel lens.

[0015] According to different embodiments, a dazzling device may comprise one or more assemblies, each comprising a power LED and the two lenses described, the device as a whole being enclosed in a waterproof case and powered by a rechargeable battery.

[0016] The external optical face of the sealed housing which emits light can be the flat face of the Fresnel lens or that of an additional window made of transparent material.

[0017] In a particular embodiment, this window can be easily replaced in case of damage.

[0018] According to another embodiment, the outer face comprises a transparent protective element that is easily replaceable in case of scratches and soiling.

[0019] According to another embodiment, the electronic circuit allows a stroboscopic operating mode in which the light pulses have an adjustable timing.

[0020] According to another embodiment, the timing of the light pulses has a period which varies randomly during its operation.

[0021] According to various embodiments, the first lens can be plano-convex and may have one or more aspherical faces.

[0022] The invention will be better understood, from the following description, which relates to a preferred embodiment, given by way of non-limiting example, and explained with reference to the accompanying schematic drawings, in Figures 1 to 4:

[0023] [Fig. 1] represents on the same graph the spectrum of the Osram LECGP2 LED (1) and the eye sensitivity curve (2), the near-superposition of the two The curves attest to the effectiveness and sensitivity of the LED radiation for glare reduction.

[0024] [Fig.2] represents in cross-section the LED (3) and a two-lens optical system comprising a first lens (4) having a flat surface (5) and a convex surface (6), and, a Fresnel lens (7).

[0025] [Fig.3] represents a device comprising two Osram LECGP2 LEDs (8), two plano-convex lenses (9) and two Fresnel lenses (10), shown in front view (H).

[0026] [Fig.4] represents the mechanical housing (12) containing the double optical system, detailed [Fig.3], having an easily replaceable transparent element (13), said housing being connected to a second box (14) containing the rechargeable battery.

Claims

Demands

1. A lighting device intended for glare comprising at least one light-emitting diode (3), generally referred to as LED, without an attached lens, driven by an electronic circuit powered by a rechargeable battery and associated with an optical system capable of recovering the luminous flux emitted by said LED and producing at a distance a substantially uniform illumination, said optical system comprising at least two lenses made of transparent material, characterized in that the optical system comprises a first lens (4) whose distance to the surface of the LED is less than the central thickness of said first lens and a second lens (7) which is a so-called Fresnel lens.

2. Device according to claim 1 characterized in that the lighting device comprises one or more LEDs each associated with an optical system, said device being enclosed in a mechanical housing (12) having an external face emitting light.

3. Device according to claim 2 characterized in that the mechanical housing has (12), on its light-emitting face, an external window made of transparent material.

4. Device according to claims 2 and 3 characterized in that the outer face of the mechanical housing has an easily interchangeable external transparent element (13).

5. Device according to claim 1 characterized in that the electronic circuit (14) which drives the LED allows stroboscopic light emission.

6. Device according to claims 1 and 5 characterized in that the electronic circuit (14) which controls the LED allows stroboscopic light emission whose timing of light pulses has a period which varies randomly during its operation.

7. Device according to claim 1 characterized in that said first lens (4) has a substantially flat face (5) opposite the LED (3).

8. Device according to claim 1 characterized in that the LED used is the LECGP2 model (8).