WO2010013178A1

WO2010013178A1 - Indirect light emitting device

Info

Publication number: WO2010013178A1
Application number: PCT/IB2009/053199
Authority: WO
Inventors: Corinne Lac
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2008-07-28
Filing date: 2009-07-23
Publication date: 2010-02-04

Abstract

The aim of the present invention is to propose a light emitting device providing indirect illumination with an effective and optimized use of all the light emitted by its source. To complete this aim, the invention relates to indirect light emitting device for illuminating a surface,including: -a primary reflector, and -a secondary reflector facing the primary reflector, wherein the primary reflector is designed for containing a light source and for reflecting a portion Z1 of the light emitted by the light source so as to define a focused light beam focused on a main illuminated area of the secondary reflector, then the focused light beam being reflected by the secondary reflector back to the surface to illuminate; wherein: a portion Z2 of the light emitted by the light source is not within the focused light beam; and wherein: the indirect light emitting device further comprises at least one light control element for deviating at least a part of Z2 outwards the focused light beam(according to a Direction D^A, i.e.downwards) and/or towards the focused light beam(according to a Direction D^B i.e. upwards).

Description

INDIRECT LIGHT EMITTING DEVICE

FIELD OF THE INVENTION

The invention relates to the field of light emitting devices, and more specifically to light emitting devices providing indirect illumination.

These devices can be indirect optical systems of a luminaire for Indoor or Outdoor application in urban environment (for e.g. for street lighting or pedestrian lighting).

BACKGROUND OF THE INVENTION The invention relates to indirect optical systems for lighting apparatus. Such a system generally comprises a primary reflector including a light source and a secondary reflector. As shown in enclosed Figure 1 (PRIOR ART), the principle of an indirect system is as follows: the primary reflector (Y) collects the light emission . of the light source (2') and collimates the light (3') towards a central part (5') of a secondary reflector (4'), which redirects light onto the surface to illuminate. Although most of the lamp beam (2') can be collimated within a sharp cone angle by the primary reflector (V), a part (6') of the direct source beam (e.g. 35%) is not collimated and goes outwards the central part (5') of the secondary reflector (4').

Thus, in order to prevent the direct lamp beam (6') being lost by going upward to the sky, and so providing sky glow nuisance, solutions of indirect systems on products today on the market are: to have a very large secondary reflector, which can be costly and difficult to be industrialized. to have a cut-off system like a louvre, which absorbs the undesirable lamp flux, but to the detriment of the total efficiency of the luminaire and the energy saving policy.

Moreover, it could have a negative impact on the aesthetic of the product, if it is put externally.

SUMMARY OF THE INVENTION The purpose of the invention is to fulfill at least one of the followings objects.

An object of the present invention is to propose a light emitting device providing indirect illumination with an effective and optimized use of all the light emitted by its source. Another object of the present invention is to propose a light emitting device which provides indirect illumination and which overcomes all or part of the above mentioned drawbacks.

Another object of the invention is to provide an indirect light emitting device with an optical element which controls the part of the lamp flux coming out of the primary reflector, in a way that it redirects efficiently this lamp beam in at least one additional direction different from the direction of the central collimated beam produced by the primary reflector, and preferably, in a direction closer to the direction of the central collimated beam.

Another object of the invention is to provide a (preferably indirect) light emitting device with an improved utilization factor (better downward Light Output Ratio).

Another object of the invention is to provide a (preferably indirect) light emitting device with less cumbersome secondary optical system

Another object of the invention is to provide a (preferably indirect) light emitting device whose aesthetic features are enhanced.

Thus, to address one or more of these objects, the invention proposes an indirect light emitting device including at least one light emitting source, a primary reflector designed so as to collect a part Zl of the direct light emitted by the source and to form a focused (indirect) light beam directed towards a secondary optical system designed so as to redirect said focused (indirect) light beam in the form of a lighting output beam towards the surface or the target to illuminate; said focused (indirect) light beam (preferably a substantially conical beam) being focused on to a main optical area (preferably the centre) of the secondary optical system.

The improvement according to the invention consisting essentially in controlling a portion Z2 of the light emitted by the light source which is not within the focused (indirect) light beam, which corresponds to the direct light emitted by the light source (the lost part of the flux), by deviating Z2, preferably towards the focused (indirect) light beam and/or in a direction opposed to the direction of said focused (indirect) light beam. The secondary optical system is preferably a reflector.

In other words, the indirect light emitting device for illuminating a surface, according to the invention includes:

- a primary reflector, and

- a secondary reflector facing the primary reflector, wherein the primary reflector is designed for containing a light source -and preferably including a light source- and for reflecting a portion Zl of the light emitted by the light source so as to define a focused light beam focused around an axis on a main illuminated area of the secondary reflector, then the focused light beam being reflected by the secondary reflector back to the surface to illuminate; wherein: a portion Z2 of the light emitted by the light source is not within the focused light beam; and wherein: the indirect light emitting device further comprises at least one light control element for deviating at least a part of Z2.

Preferably, the light control element is designed for deviating at least a part of Z2 outwards the axis of the focused light beam (according to a Direction D^A which is preferably a direction opposed to the direction of the focused - or the indirect- light beam); and/or towards the axis of the focused light beam (according to a Direction D^B which is preferably a direction selected so as to move Z2 closer to the focused - or the indirect- light beam, or the direction of the focused - or the indirect- light beam). D^A, D^B can be for example respectively downward and upward, if the light source is down and the secondary optical system is up.

The focused light which is focused onto a main illuminated area of the secondary reflector might be symmetrical or asymmetrical around a main axis.

The main axis of the focused light beam, is e.g. the optical axis of said beam, can be either different from the main axis X-X of said secondary reflector, or close to said axis X-X, or confused with axis X-X. Advantageously, the axis of the main illuminated area of the secondary reflector is the main axis X-X of said secondary reflector. In practice, it could be e.g. the central axis of the secondary reflector.

The invention relies on an optical element which controls this part Z2 of the lamp flux which is out the focused -or indirect- light beam coming from the primary reflector, in a way that it redirects efficiently this residual (or lost) lamp flux preferably in the direction(s) D^A and/or D^B.

The main focused -or indirect- light beam is preferably a substantially conical beam of an angle lower than 30°, more preferably lower than 20°, more preferably lower than 15°, more preferably lower than 10°, more preferably lower than 5°.

Thanks to these features, such light emitting device has notably the following advantages: - increase of the utilization factor (better downward Light Output Ratio) , due to the redirected downward part of flux in D^A .

- and/or decrease of the dimension of the secondary optical system , due to the directed upward part of the flux in D^B . - less spill light, due to the part of flux redirected downward by the optical system.

In various embodiments of the lighting device of the invention, one may have recourse to at least one and/or other of the following features: i. The (non-focused or direct) light control element is designed so as to direct Z2, mainly in the direction D^A, and secondarily in the direction D^B, towards the centre of the secondary reflector. ii. The (non-focused or direct) light control element is designed so as the light deviated outwards the main axis X-X (in the direction D^A) is directed towards the surface to illuminate. iii. The (non- focused or direct) light control element is able to reflect and refract the main part of Z2 in the direction D^A and to refract at least some of the remaining part of Z2 in the direction D^B. iv. The (non-focused or direct) light control element comprises at least one prismatic lens, said lens preferably being a Fresnel lens and having preferably a saw-tooth profile in which each tooth corresponds to a prismatic rib including at least three optical surfaces Sl, S2, S3: the entrance surface Sl, the reflective surface S2 and the exit surface S3. v. The (non- focused or direct) light control element is characterized in that:

*.at least one of the entrance surfaces Sl allows a light transmission within the prismatic rib towards S2 and S3,

*.at least one of the reflective surfaces S2 is intended to reflect some rays of Z2 in a direction D^c,

*.at least one of the exit surfaces S3 is intended to refract, in the direction D^A, the rays reflected by S2 in the direction D^c and to refract, in the direction D^B, all or part of the other rays entered into the light control element through the entrance surface S 1. vi. S3 is on an outer side of the light control element, and Sl and S2 are on an inner side of the light control element. Sl and S2 of the light control element are defined by the following angles being orientated from a reference plane P perpendicular to S3 towards S3: 50° < al < 70° preferably 55° < al < 65°; 165° < a2 < 185° preferably 170° < a2 < 180°. vii. The angle a2 is chosen as such the angle between S3 and the light beam issued from Z2 deviated by the light control element in the direction D^B is lower than the angle between S3 and the non-deviated Z2 light beam in the absence of light control element. viii. The (non-focused or direct) light control element is characterized in that the angle a2 is chosen as such the angle between S3 and the light beam issued from Z2 deviated by the light control element in the direction D^B is, at least 10%, preferably 30 %, and more preferably 50 %, lower than the angle between S3 and the non-deviated Z2 light beam in the absence of light control element, ix. the light control element is arranged to be located at the circumference of the outlet of the primary reflector. x. In a preferred embodiment, the light control element is a separate piece arranged to be borne by said primary reflector or is integral with the primary reflector xi. Advantageously, the (non-focused or direct) light control element is in transparent material, e.g. glass, polymethacrylate or other plastics. The incident advantage is an aesthetical one: this the (non-focused or direct) light control element appears illuminated when viewed by an observer at about one luminaire height distance from it, so giving a shiny effect at night when the luminaire is switched on . During the day too, the transparent element will enhances the aesthetic feature of the luminaire. xii. The light emitting device is characterized in that the light source comprises at least one Light Emitting Devices (LEDs).

The primary reflector is preferably a paraboloid, and preferably a paraboloid of revolution, in which the light source is located substantially at the focus. According to a variant, the primary reflector is parabolic in straight cross section and presents an elongated form. xiii. The light emitting device is characterized in that the secondary reflector comprises a plurality of concave reflective units, which can be advantageously protected against stain by a transparent plate. xiv. In another aspect, the invention concerns a light control element to be integrated within an indirect light emitting device for illuminating a surface, which indirect light emitting device comprising a primary reflector and a secondary reflector facing the primary reflector, the primary reflector being designed for containing a light source and for reflecting a portion Zl of the light emitted by the light source so as to define a focused light beam focused on a main illuminated area of the secondary reflector, then the focused light beam being reflected by the secondary reflector back to the surface to illuminate, a portion Z2 of the light emitted by the light source being not within the focused light beam; wherein the light control element is designed for deviating at least a part of Z2. Optionally, the light control element is designed for deviating at least a part of Z2 outwards the axis of the focused light beam and/or towards the axis of the focused light beam.

An advantage of at least one of these embodiments is that the transparent element will appear illuminated when viewed by an observer while giving a shiny and aesthetic effect. Moreover, the global efficiency is increased as the part of flux redirected downward by the optical system is utilized.

DESCRIPTION OF THE DRAWINGS

Other features and advantages of the invention appear from the following detailed description of one of its embodiments, given by way of non- limiting example, and with reference to the accompanying drawings. In the drawings: - Figure 1 is a scheme of an indirect light emitting device according to the prior art.

- Figure 2 is a general scheme of an indirect light emitting device for illuminating a surface, according to the present invention.

In Figures 1 & 2, the light sources of the indirect light emitting devices have 3 kinds of LEDs of different colours. Figures 1 & 2 enable to compare the invention and the prior art and emphasize the differences and the advantages of the invention over the prior art.

- Figure 3 A is an extension of Figure 3 showing a part of the (non- focused or direct) light control element.

DETAILED DESCRIPTION OF THE INVENTION

It must be noted that as used in this specification and the appended claims, the singular forms "a", "an", and "the" include plural referents unless the context clearly dictates otherwise. Unless defined otherwise, all technical and scientific terms herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

The foregoing description of preferred embodiments of the invention is not intended to be exhaustive or to limit the invention to the disclosed embodiments. Various changes within the scope of the invention will become apparent to those skilled in the art and may be acquired from practice of the invention.

In the various drawings, the same reference numerals designate identical or similar elements.

As shown on Figures 2, 3 and 3A, the indirect light emitting device for illuminating a surface (e.g. outdoor lighting), according to the invention comprises a primary reflector 1 which is faced by a secondary reflector 4, according to a main axis X-X of this latter, the outlet of the primary reflector 1 being covered by a light control element 7, for symmetrical light distribution. The light control element 7 can either be integrated into the primary reflector (1) forming only one piece with this latter or be a separate piece different from the primary reflector (1) and supported by this latter. The light control element 7 is preferably totally or partly circumferential with the outlet of the primary reflector 1. To simplify, the drawings representing the indirect light emitting device do include neither the casing which supports the reflectors 1 and 4, nor the known components of such a device, notably the electricity supply.

The primary reflector 1 contains a light source 2, which is for instance made of three (Figure 2) or two (Figures 3 & 3A) or one (not shown) LED(s) of different colours, e.g. red, blue or green. Another kind of light source may alternatively be used, such as discharge, incandescent or halogen lamp(s).

This primary reflector 1 is a paraboloid of revolution (a cup) whose internal wall is reflective of a part Zl of the light emitted by the light source 2 located substantially at the focus of the paraboloid of revolution.

Said primary reflector 1 is designed for reflecting a portion Zl of the light emitted by the light source 2 so as to define a focused light beam 3 focused around XX-axis on a main illuminated area 5 of the secondary reflector 4, the focused light beam 3 being then reflected by the secondary reflector 4 back to the surface to illuminate. A portion Z2 (Figures 3 & 3A) of the light emitted by the light source 2 is not reflected by the internal wall of the primary reflector 4. Thus, Z2 is a direct light coming from the light source 2 and is not within the focused light beam 3. Some of Z2 (preferably all) flux is treated by the light control element 7 as explained below. The light control element 7 which deviates at least a part of Z2, comprising a rim 9 with an inner side from which circular having a saw-tooth profile in which each tooth corresponds to a prismatic rib 10 including at least three optical surfaces Sl, S2, S3: an entrance surface Sl, a reflective surface S2 and an exit surface S3 (see Figure 3A). In the present embodiment, the ribs 10 are annular. All the surfaces S3 of the ribs 10 are included in the external light exit face (outer side) of the rim 9. Said external face is also designated by the reference S3 to simplify.

51 defines a light entrance of the light control element 7 for allowing then a light transmission within the prismatic rib (10) towards Sl and S3.

52 is arranged to reflect within the rim 9 some rays of Z2 in a direction D^c directed downwards (i.e. towards the surface to illuminate). To this aim, S2 may be made of or coated by an appropriate reflective coating and/or it is positioned with respect to Z2 such that the incidence angle of the considered rays of Z2 is greater than the critical angle (total reflection).

53 is intended to refract all or part of the rays reflected by Sl (rays which are directed to D^c) downwardly, into a direction D^A, so as to deviate the corresponding Z2 rays to the surface to illuminate. These rays participate therefore to the illumination of the surface. S3 is intended to refract all or part of the other rays entered into the light control element 7 towards the secondary reflector 4 and the XX-axis, into the direction D^B. These rays are therefore reflected by the secondary reflector 4 nearer from the main illuminated area 5. The size of the secondary reflector 4 can therefore be minimzed and its efficiency increased.

The light control element 7 redirects efficiently the part Z2 of the direct lamp flux coming out of the primary reflector 1, preferably outwards the focused light beam 3 (or the main axis X- X), that is to say in a direction D^A which is different and for instance opposed to the direction of the focused light beam 3. For example, D^A is rotated from the direction of the focused light beam 3 (along XX-axis) by an angle of at least 90°. In this example, this shift angle is 134° (see Figures 2 and 3A). In the drawings, D^A is downward.

The residual light of Z2 is redirected by the light control element 7 towards the focused light beam 3 (or the main axis X-X), in a direction D^B that is different, not opposed and closer to the direction of the focused light beam 3 (along XX-axis). For instance, D^B is rotated from the direction of the focused light beam 3 (along XX-axis) by an angle of less than 90° towards XX-axis. In this example, this shift angle is comprised between 12 and 39° (see Figure 3A). In the drawings, D^B is upward.

Sl and S2 are inner faces of the rim 9 which are defined by s specific angles (respectively al, a2) orientated from a reference plane P perpendicular to S3 towards S3 but also by the direct Z2 rays incidence, to provide the required downward exit angular direction D^A. Contribution for the upward flux part 6 (direction D^B) is mainly done by the double-refraction in the prismatic ribs 10 of the light control element 7, through the entrance faces Sl and the exit face S3. The specific angles of faces Sl (al) and S3, together with the choice of the refraction indicia of the light element control 7, provides an output light angle with respect to XX-axis, which is significantly lower than the output light angle which would have been obtained without the light control element 7, thus allowing the secondary reflector 4 to be reduced in size. To summarize, the angle a2 is chosen as such the angle a4 between S3 and the light beam 6 issued from Z2 and deviated by the light control element 7 in the direction D^B is lower than the angle a3 between S3 and the non-deviated Z2 light beam in the absence of light control element 7.

Example of a device according to the invention, which is defined as follows:

- Light source 2: compact high-discharge ceramic metal halide lamp, such as a CDM-T70W (from Philips);

- Primary reflector 1 : a parabolic reflector comprising a light outlet with diameter of 160 mm and a height of 80 mm, made of a brightened high-grade aluminium;

- Light source 2 is located at the focus point of the primary reflector 1;

- Light control element 7: the angle al between Sl and the plane P perpendicular to S3 and the angle a2 between S2 and P, are defined as follows: al = 174°; a2 =

60°.

The angles al, a2 are calculated in such a way, that it takes into account the lamp size extension.

In this instance, a3 is comprised between 12 & 37° and a4 = 49° (Fig. 3A). With this device, the size of the main illuminated area 5 decreases by about 40%. This means that the total reflective surface of the secondary reflector 4 may be reduced by about 40%, and therefore the diameter of the secondary reflector 4 may be reduced by about 40%. The constituent material of the light control element 7 may be a moulded transparent plastic such as a polymethacrylate in this present example. The secondary reflector 4 may comprise a plurality of concave reflective units 11 which can reflect back to the surface to illuminate, the focused light beam 3 and the light flux 6 deviated by the light control element 7. These concave reflective units avoid glowing drawbacks. Such concave reflective are notably described in CH 627252A5.

The secondary reflector 4 can be made of a moulded plastic such as a polymethacrylate and the reflective surface of the concave reflective units 11 can be coated by an appropriate reflective coating. The concave reflective units 11 may be covered by or bonded with a transparent material for protecting the reflective surfaces of the units 11 from dust and other contaminants. This material is made such that, once formed on the concave surface units 11, he exhibits a flat surface which is easier to clean than a matrix of concavities.

The indirect light emitting device is for instance a luminaire for Indoor or Outdoor application in urban environment (for e.g. for street lighting or pedestrian lighting).

Alternatively, the whole reflective surface of the secondary reflector 4 may have a concave or convex shape, e.g. in a conical shape having a small height, symmetrical or asymmetrical with respect to a main axis.

The secondary reflector 4 may comprise a metallic material, such as Aluminium, or may be made of a plastic material with a metallic reflective surface.

Claims

C L A I M S

1. An indirect light emitting device for illuminating a surface, comprising: - a primary reflector (1), and - a secondary reflector (4) facing the primary reflector (1), wherein the primary reflector (1) is designed for containing a light source (2) and for reflecting a portion Zl of the light emitted by the light source (2) so as to define a focused light beam (3) focused around an axis on a main illuminated area (5) of the secondary reflector (4), then the focused light beam (3) being reflected by the secondary reflector (4) back to the surface to illuminate; wherein: a portion Z2 of the light emitted by the light source (2) is not within the focused light beam

(3); and wherein: the indirect light emitting device further comprises at least one light control element (7) for deviating at least a part of Z2.

2. An indirect light emitting device according to claim 1, wherein the light control element (7) is designed for deviating at least a part of Z2 outwards the axis of the focused light beam (3) (according to a Direction D^A) and/or towards the axis of the focused light beam (3) (according to a Direction D^B).

3. An indirect light emitting device according to claim 2, wherein the light deviated outwards the axis of the focused light beam (3) is directed towards the surface to illuminate.

4. A light emitting device as claimed in claim 2, wherein the light control element (7) is able to reflect and refract a part of Z2 in the direction D^A and to refract another part of Z2 in the direction D^B.

5. A light emitting device as claimed in claim 2, wherein the light control element (7) comprises at least one prismatic lens, said lens preferably being a Fresnel lens (9) and having preferably a saw-tooth profile in which each tooth corresponds to a prismatic rib (10) including at least three optical surfaces Sl, S2, S3: the entrance surface Sl, the reflective surface S2 and the exit surface S3.

6. A light emitting device according to claim 5, wherein

* at least one of the entrance surfaces Sl allows a light transmission within the prismatic rib (10) towards S2 and S3, * at least one of the reflective surfaces S2 is intended to reflect some rays of Z2 in a direction D^c,

* at least one of the exit surfaces S3 is intended to refract, in the direction D^A, the rays reflected by S2 in the direction D^c and to refract, in the direction D^B, all or part of the other rays entered into the light control element (7) through the entrance surface S 1.

7. A light emitting device as claimed in claim 5 or 6, wherein S3 is on an outer side of the light control element (7), Sl and S2 are on an inner side of the light control element (7), and wherein Sl and S2 of the light control element (7) are defined by the following angles being orientated from a reference plane P perpendicular to S3 towards S3: 50° < al < 70° preferably 55° < al < 65°;

165° < a2 < 185° preferably 170° < a2 < 180°.

8. A light emitting device as claimed in claim 7, wherein the angle a2 is chosen as such an angle a4 between S3 and the light beam issued from Z2 deviated by the light control element (7) into the direction D^B is lower than an angle a3 between S3 and the non-deviated Z2 light beam in the absence of light control element (7).

9. A light emitting device as claimed in claim 1, wherein the light control element (7) is arranged to be located at the circumference of the outlet of the primary reflector (1).

10. A light emitting device as claimed in claim 9, wherein the light control element (7) is a separate piece arranged to be borne by said primary reflector (1) or is integral with the primary reflector (1).

11. A light emitting device as claimed in claim 1, wherein the primary reflector (1) is a paraboloid, and preferably is a paraboloid of revolution, in which the light source (2) is located substantially at the focus.

12. A light emitting device as claimed in claim 1, wherein the light source (2) comprises at least one Light Emitting Device (LED).

13. A light emitting device as claimed in claim 1, wherein the secondary reflector (4) comprises a plurality of concave reflective units (11).

14. A light control element (7) to be integrated within an indirect light emitting device for illuminating a surface, which indirect light emitting device comprising a primary reflector (1) and a secondary reflector (4) facing the primary reflector (1), the primary reflector (1) being designed for containing a light source (2) and for reflecting a portion Zl of the light emitted by the light source (2) so as to define a focused light beam (3) focused on a main illuminated area (5) of the secondary reflector (4), then the focused light beam (3) being reflected by the secondary reflector (4) back to the surface to illuminate, a portion Z2 of the light emitted by the light source (2) being not within the focused light beam (3); wherein the light control element (7) is designed for deviating at least a part of Z2.

15. A light control element (7) according to claim 14, wherein the light control element (7) is designed for deviating at least a part of Z2 outwards the axis of the focused light beam (3) and/or towards the axis of the focused light beam (3).