Platelike lighting device

Abstract: The light radiation beam emitted by a source with finite dimension, integrated within a transparent plate (3), in contact therewith, is initially reflected inside the plate (3) by a first reflecting or semi-reflecting planar surface (6) towards a second planar reflecting surface (8). Both reflecting surfaces (6, 8) are constituted by portions with an irregular profile provided a the two faces of the transparent plate (3), without applying a reflective coating.

Description: The present invention relates to the field of lighting systems, such as outer and inner lighting systems for motor vehicles, lighting systems for buildings, lighting systems for safety signals and road or railway signals, as well as lighting systems for scientific apparatus, laser processes, test or inspection apparatus, measurement systems such as velocimeters, reading or writing systems of the compact disk type, radar sensors for recognizing obstacles or the shape of objects, optical scanning systems, display lighting systems or warning lights. In particular, the invention relates to lighting devices of the type disclosed for example in EP-A-0 426 248. The correction of vergence of light beams, particularly those emitted by solid state light sources such as LED or lasers, is usually associated with two main requirements: the reduction of the thickness, i.e. the dimension along the optical axis, of the overall optical system and uniformity of the light beam coming out of the system. In a lighting system, the use of a source or matrix of sources without using lenses is not accepted since it does not satisfy the requirement for uniformity of the light beam through the whole emitting surface. In a conventional system such as that diagrammatically shown in figure 1 of the annexed drawings, the divergence of a LED light source 1 is controlled by a lens system 2 aligned on the axis of source 1. Once the diameter of lens 2 is chosen, the thickness of the source-lens system is determined by the divergence of light beam 3 emitted from source 1. If source 1 emits a very divergent light beam (figure 2), the thickness can be partially reduced. However this is achieved to the detriment for the system efficiency. Indeed, in this case beam 3 reaches the first interface of lens 2 at a high incidence angle and therefore is partially reflected backwardly as shown at 4. Moreover, in order that the lens may act efficiently on the beam vergence it is necessary that it has highly curved surfaces. Thus, the lens volume and complexity of manufacture increase. A further problem associated with this solution is the assembling of the system. It is in fact necessary to provide a casing which keeps source 1 and lens 2 spaced apart from, and aligned with each other. This implies a further increase in the weight and complexity of the system. In order to overcome said drawbacks, the present invention provides a lighting device having the features indicated in the annexed claim 1. Further advantageous features and preferred embodiments are defined in the remaining claims, depending from claim 1. The invention also provides a lighting system as defined in claim 7. The invention will be now described with reference to the annexed drawings, given purely by way of non limiting example, in which: figure 1 is a diagrammatic view of a conventional lighting system, including a solid state source of the LED or laser type; figure 2 shows a further known system with a source having a very divergent light beam and a highly curved lens; figure 3 is a cross-sectional view of a first embodiment of a micro-telescope lighting device according to the invention, including a plate with curved surfaces; figure 4 shows a variant of figure 3; figure 5 shows a further variant of figure 3 having an asymmetrical confiquration; figure 6 shows a further variant of figure 5; figure 7 shows how the reflectivity degree of the device is affected by the first reflecting surface; figure 8 shows a variant using a polychromatic source constituted by a single source or a number of separate adjacent sources; figure 9 shows a further variant including a source outside of the plate provided with a mirror which directs part of the beam into the plate, and figure 10 shows a cross-sectional view of a further embodiment of the invention obtained by providing a matrix of micro-telescope lighting devices. According to the invention, the vergence of the light beam emitted by a source of finite dimension is varied by a micro-telescope optical system integrated within a transparent plate. With reference to figure 3, a light source 1 emits a beam 2 of light rays whose divergence depends upon the construction of the source itself. The rays are emitted towards a transparent plate 3, constituted of a plastic or glass material, where they reach a first interface 4 on which they are subject to a partial reflection and refraction. The refracted rays 5 reach a first planar surface 6, (located on the face of the plate 3 remote from the source) and obtained by carving of the plate, which reflects the rays towards a second reflecting surface 8 located on the face of plate 3 which is closer to source 1, also formed by carving of the plate, which corrects the vergence of the beam 7 into a pre-established direction. The plate 3 acts as a light guide provided with an integrated micro-telescope. The analytical expression of the two reflecting surfaces 6, 8 is determined as a function of the features of the beam emitted by source 1, the material forming plate 3 and the features which the beam going out of the plate 3 must have. In its more complex configuration, the system is provided with a focal power at its second interface 6, i.e. the light beam is again varied in its distribution and vergence. The reflecting surfaces 6, 8 are obtained, without applying a layer of reflecting material on the surface of plate 3, but simply as a result of the provision of portions with an irregular profile of the plate faces. The solution of figure 4 has a configuration with curved surfaces located on the same side of plate 3. Figures 5,6 show solutions similar to those of figures 3, 4 but with an asymmetrical arrangement. With reference to figure 7, the reflectivity coefficient of surface 6 depends upon the refraction index of plate 3, the polarization state of the beam, the wavelength of the radiation and the inclination of surfaces 6. When this inclination becomes greater than the value corresponding to total internal reflection, the whole beam is reflected inside the guide towards the second planar surface 8. Conversely, a portion of the beam is transmitted directly. Thus, a viewer sees the device with no dark areas. The second interface appears as emitting a uniform light beam over the whole surface. On the basis of this principle, it is possible to transform the non polarized state of the beam coming into the guide into a beam with controlled polarization. Source 1 may be integrated directly in the plate. By providing surfaces 6, 8 with a circular cross-section it would be possible to obtain a beam with a circular cross-section. Conversely, by providing surfaces 6, 8 with a pyramidal configuration or with the configuration of a truncated pyramid, it is possible to obtain a beam with a square or rectangular cross-section. In the solution of figure 8, the micro-telescope lighting device is used with a polychromatic source beam emitted by a single source or many adjacent separate sources. In figure 9, the source is outside of the plate and is provided with a mirror which contributes to direct a part of the radiation towards plate 3. A coating or a refractive surface placed on the first interface 4 may cause a portion of the spectrum to be reflected, the remaining portion being transmitted. Figure 10 shows a cross-section of a matrix of micro-telescope lighting devices, which covers a large surface, such as the surface of a lighting system for a safety signal, or a side or central car light or a lighting device for the passenger compartment of a car, or a device for road signals, for traffic lights, for railway signals, for domestic and industrial building lighting systems, for scientific apparatus, for inspection systems, for laser devices, for measure systems such as velocimeters. The matrix can be constituted by elements different from each other, i.e. in which the beams are generated with different vergence and shape. Naturally, while the principle of the invention remains the same, the details of construction and the embodiments may widely vary with respect to what has been described and illustrated, without departing from the scope of the present invention as defined in the claims.

Claims: A lighting device comprising a transparent plate (3), having opposite first (4) and second major parallel faces, and a light source (1) arranged immediately adjacent to said first major face of the plate or incorporated within the plate and emitting a light beam (2, 5, 7, 9) having a predetermined divergence, said first and second major faces having respectively a first (8) and a second (6) surface portion such that part of the light beam emitted from the light source is directed towards said second surface portion, reflected by said second surface portion by internal reflection towards the first surface portion, reflected by said first surface portion by internal reflection towards said second major face and transmitted by the second major face, at least said second surface portion being constituted by the surface of a recess formed in said second major surface of the plate and having a surface shaped profile arranged with respect to the light source and cooperating with the first surface portion so that a section of the light beam emitted by the light source is reflected by total internal reflection and another section is partially reflected by partial internal reflection and partially transmitted by said second surface portion, and the light reflected by said first and second surface portions and transmitted by the second major face emerges from the second major face as an expanded light beam having a predetermined shape and a different vergence than the light beam emitted by the light source. Lighting device according to claim 1, characterized in that the light source is a solid state source of the LED or laser type. Lighting device according to claim 1, characterized in that the transparent plate (3) is constituted of a plastic or glass material and acts as transparent or coloured guide for the radiation. Lighting device according to claim 1, characterized in that the light source (1), with associated electric and electronic components, is integrated within the transparent plate (3). Lighting device according to claim 1, characterized in that one of said first and second surface portions (6, 8) has a shape such as to generate a light beam going out of the plate having a square or rectangular cross-section. Lighting device according to claim 1, characterized in that the one of said surface portions with a greater size has a predetermined geometric cross-section, for example rectangular, hexagonal or starshaped, so as to generate a beam having a similar cross-section. Lighting system, including a matrix of lighting devices integrated within a transparent plate member (3), each lighting device being a lighting device as set forth in any of the previous claims with the respective transparent plates being constituted by said transparent plate member, the lighting devices being arranged so that the second face of the plate is totally covered by the cross-sections of the emerging radiation beams. Lighting system according to claim 7, characterized in that the lighting devices constituting said matrix integrated in said transparent plate member (3) are different from each other, in order to generate separate light beams. Lighting device according to claim 1, characterized in that said first and second surface portions (6, 8) are constituted by pyramidal surfaces or surfaces with the shape of a truncated pyramid, which are curved in the faces of the plate (3). Lighting device according to claim 1, characterized in that it has a symmetrical arrangement around the optical axis of the illumination field. Lighting device according to claim 1, characterized in that it has an asymmetrical arrangement around the optimal axis of the illumination field.

Inventors: PERLO PIERO, SINESI SABINO, PERLO, PIERO, SINESI, SABINO
Applicants: FIAT RICERCHE, C.R.F. SOCIETA CONSORTILE PER AZIONI
Application year: 1996
Main classification: G02B27
IPC codes: G01P21