Lighting device

Abstract: The device comprises a block of transparent material (1) delimited by a pair of opposite surfaces, a front surface (2) and a rear surface (3) and a source of light radiation (4) located between said surfaces: cavities (5) are formed in the rear surface (3), each of which cavities is delimited at least by one surface (6) which forms a predetermined angle with the rear surface (3) and diffraction means (7) are located on the front surface (2), on which means the light rays reflected by the rear surface (3) are incident and by which means these rays are diffracted so as to give a light flux having predetermined optical characteristics.

Description: The present invention relates to a lighting device which is particularly suitable for use in lighting both on the inside and on the outside of a motor vehicle. Lighting devices designed for this use in which the light flux is generated by an emitting surface, are known e.g., from the IBM Technical disclosure Bullettin, vol. 33, no. 9 of February 1991; these devices comprise a source of light radiation in which the light is directed in a substantially parallel direction to the emitting surface and a plurality of optical devices which are able to transmit the light rays from the source in predetermined directions. The abovementioned means are usually made up of lenses, directional prisms, reflectors, diffusers or of systems of such prisms. Devices of this type have proved to be somewhat complex in terms of construction as a result of the large number of components and of the shape of some of these; also, the light flux produced using these devices cannot meet all the requirements set in connection with motor vehicle lighting; furthermore, because such devices take up a lot of space, they cannot be used in certain cases owing to the limited space available for housing them. The object of the present invention is to produce a lighting device, in particular for use on motor vehicles, which overcomes the drawbacks described and, therefore, which is structurally very simple, compact, and able to emit a light flux having the desired optical characteristics. This object is achieved through a lighting device as claimed in Claim 1. In order to give a clearer idea of the lighting device of the invention, a more detailed description will now be given by way of example and with reference to the figures of the attached drawings in which: Fig. 1 is a perspective view of a part of the device; Fig. 2 is a cross-section thereof. The device basically comprises a block of transparent material 1 delimited by a pair of converging surfaces, a front surface 2 and a rear surface 3, and a source of light radiation, indicated as a whole by the reference 4, and which is located between the planes bearing the abovementioned surfaces. Cavities 5 are formed in the rear converging surface 3, each of which cavities is delimited at least by one surface 6 which forms a predetermined angle with the rear converging surface 3; this angle is selected, as will be more fully described later, so that the rays emitted by the light source 4 and which are incident on the surfaces 6 are reflected towards the front surface 2. According to a variant embodiment not shown, there are no cavities 5 in the rear surface 3: instead, a layer of material having total reflection and high scattering properties is deposited thereon. Diffraction means 7 of a known type, either with phase modulation or with intensity modulation or consisting of holograms (for example of the computer generated holograms type) are located on the front surface 2; advantageously these diffraction means 7 can make up a set of lenses 8 of the Fresnel or Kinoform type. These lenses can be circular, as shown in the figure, or else they can be square, rectangular, hexagonal or pentagonal. There can be any number of lenses 8, these being connected together by a supporting element 9 and usually arranged so as to completely cover the front surface 2. The diffraction means 7 can comprise reliefs which are cut directly into the front surface 2, or which can be formed on a supporting sheet made of a suitable material which is then attached to the abovementioned surface. The diffraction means can form part of a computer generated hologram of the type with phase modulation or with amplitude modulation, which hologram is recorded directly on the front surface 2, or on a support of transparent material which is then attached to said surface; this hologram can be of any type known per se and able to produce any pattern and which therefore can comprise, for example, a plurality of adjacent holograms so as to obtain a predetermined distribution of the light flux emitted. The reliefs on the diffraction means 7 can be produced, in a known manner, from a master diffraction surface which is prepared for example using a multilevel process of the type with binary diffractive optics; replication can be carried out using microelectronics, by means of direct moulding, by means of "embossing" or by means of any other technique used in the replication of diffractive optics. If the element 9 supporting the diffractive reliefs is made of a sheet of plastic, the latter can be advantageously attached to the surface 2 using a suitable adhesive and can be covered with a suitable protective layer. Each of the cavities 5 advantageously consists of a longitudinal groove formed in the rear converging surface 3, while the light source 4 is housed in another longitudinal groove 10 in the block, set in the top surface 11 of said block. The groove 10 is shaped so as to maximise the coupling between the source and the light guide. For this purpose a mastic or more generally an adhesive having a suitable refractive index can be placed between the source and the light guide. Advantageously the source of light radiation 4 is a linear source and can be given a reflective coating 19 so as to increase the overall efficiency of the system. The axis is parallel that of the groove in which said source is housed. According to an alternative version, this source comprises a plurality of light emitters (not shown) arranged along an axis which is substantially parallel to that of the groove in which said source is housed. The lighting device described works in the following way. A light ray 15 (Fig. 2) emitted by the source of light radiation 4 towards the rear surface 3 is incident on the surfaces 6 of the cavities 5 and is reflected by them towards the front converging surface 2, thereby forming a ray 16; this ray is incident on the diffractive projections of one of the lenses 8, is diffracted by them and emerges from said lenses to form the ray 18. The rays 17 from the light source 4 which are directed towards the front converging surface 2 are directly incident on the lenses 8 and they too emerge therefrom in the form of diffracted rays 18. By suitably selecting the pattern of projections of the lenses 8 it is possible to obtain, from the rays emitted by the surface 2, a predetermined distribution of the light flux because as a result of the diffractive action exerted by said lenses it is possible to control, at each point of the light flux emitted by the device, the direction and the intensity of the light emitted, in such a way that said flux is distributed in a predetermined pattern. In this way the light flux is distributed in a way similar to that obtained using the usual prism means found in lighting devices of the prior art. The particular pattern of diffractive reliefs of the lenses 8 can also be used to effect chromatic control over the light flux exiting the surface 2. This is because the action exerted by these lenses on the incident rays also depends on the wavelength of the rays themselves: it is therefore possible to obtain a light flux exiting the device which is of a predetermined colour or which has a desired chromatic distribution within the flux itself. This feature enables particular light patterns to be obtained and lends itself therefore to generating effects which are particularly useful in the production of lighting devices for use on motor vehicles. In the case where the device of the invention does not have any cavities 5, and the rear surface 3 is smooth and coated with a layer of material having total reflection and high scattering properties, rays (similar to the rays 16 in Fig. 2) strike the diffraction means 7 after originating from the source 4 and being reflected by said surface; hence, the operating method described earlier applies in this case also. It is clear that modifications and variations may be made to the described embodiments of the present invention without departing from the scope of the invention itself. In particular, the device can consist of a block of transparent material delimited by a pair of surfaces, a front surface 2 and a rear surface 3, which are mutually parallel rather than convergent, as has been described with reference to the preceding embodiments; thus, in this case too, the rays emitted by the light source 4 are reflected by the rear surface 3 towards the diffraction means 7 located on the front surface 2, and are diffracted by these means to give the desired light flux.

Claims: Lighting device comprising a block (1) of transparent material delimited by a pair of opposite surfaces, a front surface (2) and a rear surface (3), and a source of light radiation (4) located between the planes bearing said surfaces, said rear surface (3) being provided with means capable of reflecting the light rays from said source which are incident on said rear surface towards said front surface; characterised in that diffraction means (7) are located on said front surface (2), on which means the light rays reflected by said rear surface (3) are incident and by which means these rays are diffracted so as to give a light flux, emerging from said front surface (2), having predetermined optical characteristics; said diffraction means being constituted by a plurality of single diffraction elements carried side by side on said front surface (2). Device according to Claim 1, characterised in that said front (2) and rear (3) opposite surfaces of said block are convergent in the direction opposite to said light source (4). Device according to Claim 1 or 2, characterised in that cavities (5) are formed in said rear surface (3), each of which cavities is delimited at least by one surface (6) which forms a predetermined angle with said rear surface (3), so as that relieves are formed on said rear surface (3). Device according to Claim 3, characterised in that each of said cavities (5) consists of a longitudinal groove formed in said rear surface (3), said light source being housed in another longitudinal groove (10) in said block. Device according to Claims 1, 2 or 3, characterised in that a layer of material having total reflection and high scattering properties is deposited on said rear surface (3). Device according to one of the preceding claims, characterised in that said diffraction means (7) comprise a plurality of diffractive lenses (8). Device according to Claim 6, characterised in that said diffractive lenses are of the Fresnel or Kinoform type. Device according to one of the preceding claims, characterised in that said diffraction means (7) are of the type with phase modulation. Device according to one of Claims 1 to 7, characterised in that said diffraction means (7) are ofthe type with amplitude modulation. Device according to one of the preceding claims, characterised in that said diffraction means (7) comprise diffractive projections located on said front surface (2), so as to form a predetermined configuration. Device according to claim 10 characterised in that said diffractive projections are cut into said front surface (2) of the block of transparent material (1). Device according to claim 10 characterised in that said diffractive projections are formed on a sheet of material (9) which is attached to said front surface (2) of said block block of transparent material. Device according to one of the preceding claims, characterised in that said diffraction means (7) comprise at least one hologram of the computer generated hologram type. Device according to Claim 13, characterised in that said diffraction means (7) comprise a series of independent holograms, arranged next to one another. Device according to one of the claims 13 or 14 characterised in that said hologram is recorded on said front surface (2) of said block of transparent material. Device according to one of the claims 13 or 14 characterised in that said hologram is recorded on a sheet of material which is attached to said front surface (2) of said block oftransparent material. Device according to one of the claims 4 to 16 characterised in that said source of light radiation (4) is a light source whose axis is parallel to that of said groove (10) in which said source is housed. Device according to one of the claims 4 to 16, characterised in that said source of light radiation (4) comprises a plurality of light emitters arranged along an axis which is substantially parallel to that of said groove in which said source is housed.

Inventors: MASUELLI STEFANIA, PERLO PIETRO, MASUELLI, STEFANIA, PERLO, PIETRO
Applicants: MAGNETI MARELLI SPA, MAGNETI MARELLI S.p.A.
Application year: 1993
Main classification: F21V8
IPC codes: G02B6, F21S8, F21V5, F21V8