WO2010146494A1

WO2010146494A1 - Lighting device.

Info

Publication number: WO2010146494A1
Application number: PCT/IB2010/052527
Authority: WO
Inventors: Bertrand J.B. Navarro
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2009-06-16
Filing date: 2010-06-08
Publication date: 2010-12-23

Abstract

The invention relates to a lighting device comprising a back reflector (1) constructed around a main axis. The back reflector (1) comprises at least one part which is tilted around an axis perpendicular to the main axis of this back reflector (1) to obtain a disymmetrical light distribution at the outlet of the back reflector.

Description

LIGHTING DEVICE

FIELD OF THE INVENTION

The invention relates in general to lighting device and more particularly to a lighting device providing a di- symmetrical light beam to optimise the illumination of an area of interest by focusing the light beam energy onto the area of interest.

BACKGROUND OF THE INVENTION

It is well known that lighting device comprising a conical reflector 1, or more specifically a parabolic reflector 1, with an optical centre on an optical main axis which lies in an optical main plane, a light source 2 positioned into the parabolic reflector and a front glass 3 positioned at the outlet of the reflector 1, as depicted in figure 1 showing a lighting device of prior art, provides a symmetrical light distribution as depicted in figure 2A. It is intended that "symmetrical light distribution" means a symmetrical polar intensity distribution, i.e. the light is evenly spread around the desired direction.

It is also well known asymmetrical projectors providing a symmetrical light distribution around their aiming axis. For example, US 4,742,440 discloses such a lighting device. The lighting device comprises a main parabolic reflector on whose side wall an opening is provided, in correspondence of which an additional reflector segment is externally provided. This additional reflector segment has the same curvature of the main reflector and is held spaced apart from the main reflector. Moreover, US 4789923 discloses a lighting device designed for improved roadway illumination to produce uniform illumination over a specified area. The lighting device comprises a reflector having a concave interior surface formed with bands of reflective facets. The groups of facets are organized in bands which extend arcuately around the interior of the reflector, each facet being oriented to reflect light to a desired luminance centre on a roadway surface.

Such lighting devices are usually called asymmetrical projectors and provide a symmetrical light distribution as illustrated in figure 2B in the same manner as symmetrical projectors.

In order to maintain a good level of illumination and uniformity, such projectors are aimed at the edge of an area of interest. Consequently, because of the regular symmetrical distribution of these projectors, half of the light is lost. To overcome above-mentioned limitation, a need exists for a lighting source providing a high level of illumination and uniformity on the edge of an area of interest without wasting too much light outside of the area of interest.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a lighting device comprising at least a back reflector constructed around a main axis , wherein the back reflector comprises at least one part which is tilted around an axis perpendicular to the main axis of the back reflector to obtain a di- symmetrical light distribution at the outlet of the conical reflector. It is intended that a "di- symmetrical light distribution" is a light distribution comprising a higher distribution on one side of the main axis compared to the other.

Preferably, the back reflector is a conical, or more particularly a parabolic, reflector. Preferably, the tilted part of the back reflector is concentric with the main axis.

In one embodiment, the bottom part of the reflector is tilted around the axis perpendicular to the main axis of the reflector according to a first angle.

Preferably, the reflector comprises at least three parts tilted around the axis perpendicular to the main axis of the reflector. Accordingly, the bottom part of the reflector is tilted around the axis perpendicular to the main axis of the reflector according to a first angle and the reflector comprises two opposite lateral parts that are tilted around the axis perpendicular to the main axis of the reflector according to a second angle and respectively a third angle.

Moreover, tilting angles of the two lateral parts may be lower than the tilting angle of the bottom part. Each opposite lateral parts may extend from a portion of the light outlet edge of the back reflector. In the case of a parabolic back reflector, each opposite lateral part may extend from a portion of the light outlet edge of the back reflector to a circumferential line consisting in the points of projection, perpendicular to the main axis, of the focal point of the parabola onto the back reflector. The bottom part of the back reflector may be located adjacent the ends of the opposite lateral parts which are respectively opposite the said portions.

Accessorily, the lighting device according to the invention further comprises a front glass positioned at the outlet of the reflector.

It is advantageous for obtaining a better light distribution if the front glass comprises at least one element having a prismatic effect.

It is favourable if the front glass comprises a plurality of embedded prism structures. In this manner, each portion of the glass contributes more or less to the area of interest. To determine the best pattern, the area contributing to the lost light must be identified and then a prismatic effect according to the desired deviation is determined.

Preferably, to avoid a double peak in the light distribution, the tilting angle of the bottom part of the conical reflector is substantially equal to half the light beam angle.

Optionally, the lighting device comprises at least one light source arranged within the back reflector, located for example at the focus of the parabola of a parabolic reflector.

BRIEF DESCRIPTION OF THE DRAWINGS

For a further understanding of the objects and advantages of the present invention, references should be made to the following drawings in conjunction with the accompanying descriptions and operations, wherein:

- Figure 1 shows a schematic sectional view of a symmetrical projector of prior art,

- Figure 2 A and 2B show a schematic polar intensity distribution of a symmetrical projector and an asymmetrical projector of prior art respectively,

- Figure 3 shows a perspective view of a parabolic reflector of the lighting device according to the present invention, - Figure 4 shows a schematic partial sectional view of the parabolic reflector of the lighting device according to the invention,

- Figure 5 shows a graphic representation of Cartesian distributions for symmetrical light distribution of lighting device of prior art and di-symmetrical light distribution of the lighting device according to the present invention, - Figure 6 shows a schematic polar intensity distribution of the lighting device according to the present invention,

- Figure 7 shows a perspective view of a transparent front glass comprising a plurality of embedded prism structures of the lighting device according to the invention,

- Figure 8 shows a schematic sectional view of a basic prism deviation.

DETAILED DESCRIPTION OF EMBODIEMENTS

It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

For the purpose of promoting an understanding of the present invention, references are made in the text hereof to embodiments of a lamp, only some of which are depicted in the drawings. It is nevertheless understood that no limitations to the scope of the invention are thereby intended.

Furthermore, in the embodiments depicted, like reference numerals refer to identical structural elements in the various drawings. Referring to figure 1, the lighting device according to the invention comprises, in the same manner than prior art, a back reflector 1 construed around a main axis, preferably a conical, or more specifically and more preferably a parabolic reflector 1, with an optical centre on an optical main axis which lies in an optical main plane, a light source 2 positioned into the conical reflector and optionally a front glass 3 positioned at the outlet of the reflector 1. In the case of a parabolic reflector 1, the light source may be located at the focus of the parabola in order to obtain output parallel beams.

Figure 3 is a perspective view of a back reflector 1 of the lighting device according to the present invention and shows the main elements of said back reflector 1. The back reflector 1 is construed around a main axis 10 and comprises at its bottom portion a plane 4 including a circular hole 5 in which a lighting source, not shown in the figure, can be introduced for accommodating said light source into the back reflector 1. In a particular configuration, both light source and back reflector 1 may be fixed on a common support (e.g. a post).

The back reflector 1 comprises three tilted parts. Before tilting these parts comprise:

- a bottom part 6 extending from the bottom of the back reflector 1 up to, for example, a circumferential line 12 of the back reflector 1; and

- two opposite lateral parts 7a, 7b, each extending from the edge 1 Ia, 1 Ib of the light outlet of the back reflector 1 to, for example, the circumferential line 12 or to portion of different circumferential lines. Each lateral part 7a, 7b, may have parallel lateral sides 13al_, 13a2 and l3M, 13b2.

For a parabolic back reflector 1, the circumferential line 12 may be construed from the points of projection, perpendicular to the main axis 10, of the focal point of the parabola onto the back reflector 1. Referring to figure 4, the bottom part 6 is tilted around an axis 8 perpendicular to the main axis 10 of the reflector 1 according to a first angle α. If the back reflector 1 is of parabolic shape, said tilting axis 8 preferably passes through the focal point of the parabolic reflector 1. The two opposite lateral parts 7a, 7b are tilted around the axis 8 perpendicular to the main axis 10 of the back reflector 1 according to a second angle βi and respectively a third angle β₂.

In this embodiment, the second angle βi and respectively the third angle β₂ are equal; nevertheless, it is obvious that these angles βi and β₂ can be different depending on the desired di- symmetrical light distribution without departing of the scope of the invention.

Moreover, tilting angles βi and β₂ of lateral parts 7a, 7b are preferably lower than the tilting angle α. This tilting angle α of the bottom part 6 may be substantially equal to half the light beam angle of the lighting device at the outlet of the reflector 1, in order to avoid a double peak in the light distribution. The angles βi and β₂ may be each one substantially half the value of α (due to the location of the lateral parts 7a, 7b more proximate the outlet of the back reflector 1 than the bottom partό). These values of angles may be in particular chosen for a parabolic reflector 1, especially if the aforementioned construction of the circumferential line 12 is used. It is intended that "substantially" means that the tilting angle α is equal to half the light beam angle more or less ε wherein ε is lower or equal to 5% of the light beam angle of the lighting device.

Referring to figure 5, showing a graphic representation of Cartesian distributions for symmetrical light distribution of lighting device of prior art and di- symmetrical light distribution of the lighting device according to the present invention, such tilted bottom part 6 and tilted lateral parts 7a, 7b provide a di-symmetrical light distribution. On the graph, the 0° abscissa corresponds to the main axis 10 of the back reflector 1. Everything that is on the right side of the 0° abscissa will fall out of the area of interest and thus would be lost light. Lighting device of prior art, such as symmetrical and asymmetrical projector described above, provides a symmetrical light distribution (doted line on figure 5), i.e. a symmetric Cartesian distribution in relation to the 0° abscissa, in such a manner that half the light energy is lost.

Referring to figures 5 and 6, the lighting device according to the invention provides a di-symmetric light distribution (straight line on figure 5), i.e. the Cartesian distribution is not symmetric in relation to the 0° abscissa. In this way, only a small part of light energy is lost, most of the light energy being in the area of interest.

In another embodiment, not shown on figures, the lighting device according to the invention comprises only a tilted bottom part 6.

In yet another embodiment, not shown on figures, the lighting device according to the invention comprises a tilted bottom part 6 and a plurality of tilted lateral parts 7, said lateral parts 7 being equally spaced apart or not.

Accessorily, referring to figure 7, the lighting device according to the invention further comprises a transparent front glass 3 positioned at the outlet of the back reflector 1.

The front glass 3 comprises a plurality of embedded prism structures 9. Each prism structure 9, referring to figure 8, provides a deviation of the light beam. In this manner, each portion of the front glass 3 contributes more or less to the area of interest. To determine the best pattern of the embedded prism structures 9, the area contributing to the lost light must be identified and then a prismatic effect according to the desired deviation is determined.

It should be noted that the front glass 3 can comprise only one element having a prismatic effect without departing of the scope of the invention ; nevertheless, said element having a prismatic effect does not cover the complete front glass 3 otherwise it would only result in an aiming deviation.

Moreover, it should be noted that the conical or parabolic reflector 1 could be substituted by any back reflector 1 constructed around a main axis, the optical axis preferably corresponding to said main axis, without departing from the scope of the invention.

The reflector 1 may be manufactured by any known techniques for manufacturing a reflector. For example, this reflector 1 may be made by spinning from an Aluminium leaf or panel, plated on a tool having an external surface being the negative shape of the asymmetric reflector 1 to be made. Although embodiments of the present disclosure have been described in detail, those skilled in the art should understand that they may make various changes, substitutions and alterations herein without departing from the spirit and scope of the present disclosure. Accordingly, all such changes, substitutions and alterations are intended to be included within the scope of the present disclosure as defined in the following claims.

Claims

1. A lighting device comprising at least:

a back reflector (1) constructed around a main axis (10); wherein the back reflector (1) comprises at least one part which is tilted around an axis (8) perpendicular to the main axis (10) of the back reflector so as to obtain a disymmetrical light distribution at the outlet of the back reflector.

2. Lighting device of claim 1, wherein the back reflector is a conical reflector.

3. Lighting device of claim 1, wherein the back reflector is a parabolic reflector.

4. Lighting device of claim 1, wherein the tilted part (6) of the back reflector is concentric with the main axis.

5. Lighting device of claim 1, wherein the bottom part (6) of the reflector is tilted around the axis (8) perpendicular to the main axis (10) of the reflector according to an angle α.

6. Lighting device of claim 5 wherein the reflector comprises at least three parts tilted around the axis (8) perpendicular to the main axis (10) of the reflector.

7. Lighting device of claim 6 wherein the reflector comprises two opposite lateral parts (7a, 7b) that are tilted around the axis (8) perpendicular to the main axis (10) of the reflector according to an angle βi and respectively β₂.

8. Lighting device of claim 7 wherein tilting angles βi and β₂ are lower than the tilting angle α of the bottom part (6).

9. Lighting device of claim 7 wherein each opposite lateral parts (7a, 7b) extends from a portion of the light outlet edge of the back reflector.

10. Lighting device of claims 3 and 7 wherein each opposite lateral part (7a, 7b) extends from a portion of the light outlet edge of the back reflector to a circumferential line (12) consisting in the points of projection, perpendicular to the main axis (10), of the focal point of the parabola onto the back reflector.

11. Lighting device of claim 9 or 10, wherein the bottom part (6) of the back reflector (1) is located adjacent the ends of the opposite lateral parts (12) which are respectively opposite the said portions.

12. Lighting device of claim 1 wherein it further comprises a transparent panel (3) positioned at the outlet of the reflector which may comprise a plurality of prism structures.

13. Lighting device of claim 5 wherein the tilting angle α is substantially equal to half the light beam angle.

14. Lighting device of claim 1 comprising at least one light source arranged within the back reflector.

15. Lighting device of claims 3 and 14 wherein the at least one light source is arranged at the focus of the parabola.