Lighting device that can be constructed with reduced thickness, especially a headlamp or other external vehicle lamp

Abstract

 Lighting device (10), usable as a headlamp or other external vehicle lamp, whose thickness (space requirement in terms of depth) is much less than its other dimensions, comprising at least one light source (1), a modifier/extractor (13) and at least one reflector (3) for collimating a beam of light rays from the source towards the modifier/extractor (13), which latter is designed to control the divergence and intensity distribution of the beam and deflect it through a lens (6) arranged approximately parallel to the direction of propagation of the beam, in front of the modifier/extractor; the latter is a second reflector (13) with, directly facing the lens (6), an upper surface arranged obliquely to the direction (X) of propagation of the beam in such a way that the second reflector (13) is approximately wedge-shaped in cross section in the direction (X) of propagation of the beam, which upper surface is made up of a plurality of mutually adjacent reliefs (15), each of which has, in the direction of propagation of the beam, a sawtooth profile; the peaks (20) of the reliefs (15) all lying on a continuous curve (21) of defined shape, and for each relief (15) the oblique side (16) nearest the light source (12) lies at an individually defined angle relative to the direction (X) of propagation of the beam.

Description

[0001] The present invention relates to a lighting device that can be constructed in such a way that its thickness, that is, its space requirement in terms of depth, is much less than its other dimensions, especially than the surface area of the lens. Such a lighting device is useful as a headlamp or other external vehicle lamp.

[0002] As is well known, lighting devices in many automotive applications, such as headlamps and/or other external lamps, require high power, good optical distribution of the light beam, low power consumption and small size, especially in the direction of depth, that is, parallel with the optical axis of propagation of the final light beam that is to be produced.

[0003] In order to fulfil these demands a variety of ways of making thin lighting devices are known. US Patent 5,046,805 relates to a device in which the light beam emitted by the source, transversely to the direction in which it is to be aimed, is collected by a lightguide along which the beam is transmitted by internal reflection and from which it is extracted at the desired points by means of scatterers; while Italian Patent Application No. TO94A000773 by the present Applicant discloses a device in which the light beam is collected by a lightguide defined by two mouldings presenting a plurality of appropriately angled interfaces along which the two mouldings, which are transparent, are glued by means of a layer of optical adhesive with a defined refractive index: in this way the propagation of the light beam along the guide produces, as it passes each interface, phenomena of partial refraction/reflection by means of which the light is extracted and guided.

[0004] Both the devices described therefore employ a lightguide as a modifier/extractor of the desired beam. However, they have very serious drawbacks from the point of view of achievable performance: the first device, in accordance with the cited US patent, gives excellent uniformity of illumination of the guide, but allows no control over the distribution of the light intensity and divergence of the final beam output by the device: such control is necessary in the case of automotive devices. These functions must therefore be handled, where possible, by the lens, so that manufacture is made more complex and the space requirement increased.

[0005] Contrariwise, in the second described known device, the efficiency of the lightguide can be shown to be very low: efficiency is a function of the number of interfaces and only if this number is large enough (greater than 100) is it possible to achieve more than 45% efficient extraction of the light. However, the possibility of using a large number of interfaces is limited by the physical dimensions available to the lightguide, which will be small if the space requirements of the device are to be kept down. The small dimensions of the final device are therefore achieved at the cost of light efficiency, making it necessary to use high-power lamps and/or a large number of lamps, which in turn means heavy power consumption. In addition, in this type of device, uniformity of illumination is inversely proportional to the number of interfaces. Therefore in order to obtain good uniformity the guides must be inefficient, or alternatively the reflective/refractive characteristics of each interface of the guides must be modified. This can be done either by having different dimensions for each succeeding interface, or by modifying the refractive index of the adhesive between them; however, either method introduces a complication into the manufacturing process and the problem in question is not always satisfactorily solved.

[0006] It is an object of the invention to provide a lighting device that solves the problems described above, in particular by making it possible to combine high uniformity of illumination with an equally high efficiency. It is also an object of the invention to provide a device that is compact, reliable and comparatively simple to manufacture.

[0007] The invention therefore provides a lighting device, usable as a headlamp or other external vehicle lamp, whose thickness is less than its other dimensions, comprising at least one light source, a modifier/extractor and at least one reflector for collimating a beam of light rays from the source towards the modifier/extractor, which latter is designed to control the divergence and intensity distribution of the beam and deflect it through a lens arranged approximately parallel to the direction of propagation of the beam, in front of the modifier/extractor; characterized in that the modifier/extractor is a second reflector facing the first, the upper surface, directly facing the lens, of which second reflector is arranged obliquely to the direction of propagation of the beam, in such a way that the second reflector is approximately wedge-shaped in cross section in the direction of propagation of the beam; and in that said upper surface is defined at least in part by a plurality of mutually adjacent reliefs, each of which has, in the direction of propagation of the beam, a sawtooth profile such that for each relief the oblique side nearest the light source lies at an individually defined angle relative to the direction of propagation of the beam.

[0008] Moreover, the peaks of said sawtooth reliefs all lie on a continuous curved profile of defined shape, which is preferably a complex profile made up of a plurality of curves of different equations fitted together without discontinuity up to a defined order of derivative, preferably to the second order.

[0009] The oblique sides of the reliefs are defined by respective planar or curved reflective surfaces, optionally defined by complex profiles, and said reliefs all have a constant profile, so that the oblique sides all have the same inclination, or they may differ in profile from each other, so that the oblique sides have different inclinations.

[0010] Moreover, in another aspect of the invention, the surfaces defining said oblique sides of the reliefs are given diffractive optics or microoptics, either formed directly on these surfaces or applied to them; these diffractive microoptics may optionally be formed directly on a surface of the second reflector that has no reliefs, instead of part of the sawtooth reliefs themselves.

[0011] Lastly, the lens is preferably provided with a plurality of refractive, diffractive or hybrid diffractive/refractive lenses/microlenses for receiving the light beam after the second reflector has modified and deflected it and giving it a desired definitive distribution.

[0012] Other objects and advantages of the present invention will become clear in the following description of certain non-restrictive embodiments. This description refers to the figures of the accompanying drawings, in which:

• Figure 1 is a schematic elevation of a headlamp or other external vehicle lamp constructed in accordance with the invention;
• Figure 2 is a schematic perspective view of the device of Figure 1;
• Figures 3 and 4 show examples, on an enlarged scale, of different details of the construction of the device of Figure 1; and
• Figures 5, 6, 7 and 8 illustrate different possible alternative embodiments of the device of the invention.

[0013] With reference to Figures 1 and 2, the numeral 10 is a general reference for a lighting device, in the present case a headlamp or other external vehicle lamp, that basically comprises an envelope 2 of known type, illustrated only schematically for simplicity's sake, of, for example, parallelepipedal shape and containing a light source 1 and a reflector 3, of for example parabolic profile; the envelope 2 is closed on the outside (sealed against the ingress of fluids, for example) by a transparent screen or lens 6 (Fig. 1). According to the invention, the thickness S of the device 10 measured parallel to an optical axis A along which the rays 11 produced by the device 10 are directed, is much smaller (for example by an order of magnitude) than the length L of the envelope 2, whereas it may be of any width, meaning its dimension perpendicular to the length L and to the thickness S, depending on what the lighting requirements are. The reflector 3, and the source 1, are arranged at one end 4 of the envelope 2, in such a way that the reflector 3 collimates the various light rays 9 emitted by the source 1 and directs them, parallel to each other, along a direction of propagation X - indicated by the arrow in Figure 1 and parallel with the lens 6 and with the side of dimension L of the envelope 2 - perpendicularly and on one side of the optical axis A.

[0014] Furthermore the envelope 2 also houses a modifier/extractor component, the function of which is to collect the rays 9 collimated by the reflector 3 and deflect them, with defined divergence and intensity with respect to the optical axis A through the lens 6, to form the rays 11 of the final light beam which it is desired to obtain. According to the invention, this modifier/extractor component consists of a second reflector 13 facing the reflector 3, opposite from it and in front of the lens 6, for the entire length L of the envelope 2.

[0015] The reflector 13 has a completely reflective upper surface 14 directly facing the lens 6 and arranged obliquely to the direction X of propagation of the beam of rays 9. The reflector 13 is consequently basically wedge-shaped in cross section (cutting in direction X). In addition, the surface 14 is defined, wholly or at least in part, by a plurality of mutually adjacent reliefs 15, each of which has, in the direction X of propagation of the light beam collimated by the reflector 3, a sawtooth profile (Figures 3 and 5); each relief 15 (Figures 3 and 5) is therefore defined by an oblique side 16, turned towards the light source 1 and lying at a defined angle relative to the direction of propagation X, and by an opposite side 18 situated approximately perpendicularly to the lens 6.

[0016] Both sides 16, 18 are defined, in the present example, by reflective surfaces. These surfaces may be planar, as illustrated, or may be curved, either in direction X or at right angles to this direction, the curvature being described by a single equation or, if required, by a series of different equations (complex surface), in order to control the divergence of the beam of rays 11 leaving the device 10 in the two directions perpendicular to the optical axis A.

[0017] Whichever form is adopted, according to the invention the reliefs 15 are so shaped that respective peaks 20 of said sawtooth teeth all lie on a continuous curved profile of defined shape, illustrated by a dashed line marked 21 in Figure 3. The profile 21 is such as to give the reflective surface 14 as a whole a generally concave configuration made up of all the mutually adjacent reliefs 15 put together and, depending on how the final beam of rays 11 is to be distributed and deflected through the lens 6, this profile 21 may have a single equation (may for example be parabolic or elliptical) or, preferably, be a complex profile made up of a plurality of curves of different equations (for example a parabola, a portion of an ellipse, a portion of a circle, a portion of a hyperbole, etc.) fitted together without discontinuities up to a defined order of derivative, preferably to the second order.

[0018] The profile 21 is chosen by calculation, in such a way as to find the best possible compromise between the following requirements:

• achieve initial control over the divergence of the beam of rays 11 leaving the device 10 in one of the two directions perpendicular to the optical axis A, which will subsequently be refined by the lens 6;
• smooth out the distribution of illumination on the lens 6 at the outlet of the device 10, from the combined distribution ("pattern") of intensity of the beam of rays 9 collimated by the reflector 3 and of the directly output light.

[0019] Whichever approach is adopted, the selection of the possible profile 21 is limited by the physical dimensions of the device 10, in particular by the two heights h1 and h2 (Figure 3) at the beginning and end of the component 13, which are laid down at the start of the design according to the final thickness S to be achieved. Figure 4 illustrates, though not in scale, three different possible profiles 21a, 21b and 21c and shows how the same ray 9 collimated by the reflector 3 is reflected at different angles by each profile 21, thus producing outgoing rays 11a, 11b and 11c having different divergences and striking the lens 6 at quite different points.

[0020] As illustrated in Figures 1 to 3, the teeth or reliefs 15 are all of the same profile, so that the oblique sides 16 all have the same inclination, or, in the variant illustrated in Figure 5, the reflective surface 14 of the reflector, marked 13a, is composed of reliefs 15 whose profiles differ from each other, so that the oblique sides 16 have different inclinations, in order to modify the light distribution (as is indicated by the differing divergences of the resulting outgoing rays 11) without altering the uniformity of illumination of the lens 6.

[0021] In the other possible variant illustrated not in scale in Figure 6, the reliefs 15, especially the surfaces defining their oblique sides 16, can be provided with diffractive optics or microoptics 25a and 25b, different from each other (or identical to each other), their function being the initial distribution of the desired final light beam. These optics 25a, 25b may be formed directly on the surfaces 16, as a series of microreliefs produced directly along with the component 13, which is preferably a moulding in a synthetic plastic resin, or be made, by a known technique, on respective transparent films (known and not shown), which in turn are applied to the surfaces 16 as a coating, for example by adhesive bonding.

[0022] If diffractive microoptics are employed, these may in some cases completely replace some of the sawtooth reliefs 15: in other words, in this case, some areas of the surface 14 have no reliefs 15 and only a diffractive optic. Either way, these surface 14 areas must still lie on the overall profile 21 defining the shape of the surface 14 as a whole.

[0023] Lastly, the lens 6 is provided with a plurality of refractive, diffractive or hybrid diffractive/refractive lenses/microlenses 6a (Figure 1) for receiving the light beam after the surface 14 has modified and deflected it, and giving it the desired definitive distribution. These optics 6a may likewise be formed directly on the lens 6, or on films which are then adhesively bonded to the lens 6, for example on the inside of the device 10.

[0024] The light source 1 may be of any type capable of emitting monochromatic, polychromatic, coherent, partially coherent or totally incoherent light; for instance, it may be a filament (incandescent), gas, ion-discharge, solid-state polymer, LED (optionally with suitable collimating lenses), halogen or neon lamp, or may consist of an optical fibre; if it is wished not to use the direct rays, moreover, the source 1 can be masked, as known, by a concealing shield arranged near the second reflector 13.

[0025] The example illustrated in Figures 1 and 2 uses a single source of light 1 arranged at one end 4 of the device 10; however, on the basis of the available space and of the power needed to produce the desired final light beam, many other embodiments of the device 10 are possible, two of which, marked 10a and 10b, are illustrated in Figures 7 and 8, as alternatives using more light sources.

[0026] For instance, Figure 7 shows a device 10a of elongate shape comprising a pair of opposing in-line reflectors 3, each provided with its own light source 1, and a modifier/extractor consisting of another reflector 13b in the shape of a double wedge arranged between and in line with the two reflectors 3, and defined by a pair of oblique reflective upper surfaces 14a and 14b, whose inclinations are opposite and which each face a reflector 2 and are each defined by a plurality of adjacent reliefs 15, which diminish away from a common middle top portion 34 towards the respective reflectors 3. If the lighting power needs to be increased, this variant, and also the previous one, as shown in Figures 1 and 2, can serve as an infinitely replicable module along the direction perpendicular to the side L, in which the sources 1 are arranged in succession on the same side (or on the two opposite sides).

[0027] Lastly, in the variant shown in Figure 8, a device 10c according to the invention can also be made with circular symmetry about the optical axis A: the device 10c in this case comprises a reflector 13c defined by a reflective upper surface 14 of generally conical form, formed by a plurality of annular reliefs 15, each having a sawtooth profile in the radial direction; this reflector 13c, arranged so that its axis is on the optical axis A, is arranged inside a suitable envelope 2 together with a plurality of reflectors 3, each having its own light source 1, disposed radially in a ring around the reflector 13c; at the front, the device 10c is closed by a lens 6. In this way, essentially the same operational configuration is reproduced in any radial direction defined by the axis of a reflector 3 as that of the device 10 of Figures 1 and 2.

Claims

1. Lighting device, usable as a headlamp or other external vehicle lamp, whose thickness is less than its other dimensions, comprising at least one light source, a modifier/extractor and at least one reflector for collimating a beam of light rays from the source towards the modifier/extractor, which latter is designed to control the divergence and intensity distribution of the beam and deflect it through a lens arranged approximately parallel to the direction of propagation of the beam, in front of the modifier/extractor; characterized in that the modifier/extractor is a second reflector facing the first, the upper surface, directly facing the lens, of which second reflector is arranged obliquely to the direction of propagation of the beam; and in that said upper surface is defined at least in part by a plurality of mutually adjacent reliefs, each of which has, in the direction of propagation of the beam, a sawtooth profile such that for each relief the oblique side nearest the light source lies at an individually defined angle relative to the direction of propagation of the beam.

2. Lighting device according to Claim 1, characterized in that the peaks of said sawtooth reliefs all lie on a continuous curved profile of defined shape.

3. Lighting device according to Claim 2, characterized in that said profile is a complex profile made up of a plurality of curves of different equations fitted together without discontinuity up to a defined order of derivative, preferably to the second order.

4. Lighting device according to any one of the previous claims, characterized in that said oblique sides of the reliefs are defined by respective planar surfaces.

5. Lighting device according to any one of Claims 1 to 3, characterized in that said oblique sides of the reliefs are defined by respective curved surfaces.

6. Lighting device according to any one of the previous claims, characterized in that said reliefs all have a constant profile, said oblique sides all having the same inclination.

7. Lighting device according to any one of Claims 1 to 5 characterized in that said reliefs differ in profile from each other, said oblique sides having different inclinations.

8. Lighting device according to any one of the previous claims, characterized in that at least the surfaces defining said oblique sides of the reliefs are given diffractive optics or microoptics, either formed directly on these surfaces or applied to them.

9. Lighting device according to any one of the previous claims, characterized in that said lens is provided with a plurality of refractive, diffractive or hybrid diffractive/refractive lenses/microlenses for receiving the light beam after the second reflector has modified and deflected it and giving it a desired definitive distribution.

10. Lighting device according to any one of the previous claims, characterized in that it is of elongate shape and comprises a pair of first opposing in-line reflectors, each provided with its own light source, and a second reflector in the shape of a double wedge arranged between and in line with said first reflectors and defined by a pair of oblique reflective upper surfaces, which each face a first reflector and are each defined by a plurality of said adjacent reliefs, which diminish away from a common middle top portion towards said first reflector.

11. Lighting device according to any of the previous claims, characterized in that, at right angles to the direction of propagation of the light beam which it emits, it is of a generally circular shape comprising a second reflector defined by a reflective upper surface formed by a plurality of annular reliefs, each having a sawtooth profile in the radial direction, and a plurality of first reflectors, each having its own light source, disposed radially in a ring around the second reflector.

Drawing