WO2015144350A1

WO2015144350A1 - Luminaire and light transmissive optical plate

Info

Publication number: WO2015144350A1
Application number: PCT/EP2015/052282
Authority: WO
Inventors: Fernando RODRIGUEZ MERINO
Original assignee: Koninklijke Philips N.V.
Priority date: 2014-03-28
Filing date: 2015-02-04
Publication date: 2015-10-01

Abstract

Luminaire comprising a housing for accommodating a plurality of light sources arranged along a line in a length direction. A light transmissive, optical plate extends alongside the light sources at a distance D, the optical plate has a first face facing towards the light sources. Light from the light sources is issued through the optical plate to the exterior of the housing. The optical plate has on its first face and/or its second face a micro-sized, rippled structure, said rippled structure has a smooth undulation extending solely essentially transverse to the length direction. Preferably said undulation has a periodiclength PL and amplitude A, and preferably has an aspect ratio AR defined by PL / A, with 2 <= PL/A <= 0. Spottiness of the light sources is significantly reduced, yet the energy efficacy of the luminaire is relatively high.

Description

LUMINAIRE AND LIGHT TRANSMISSIVE OPTICAL PLATE

FIELD OF THE INVENTION

The invention relates to a luminaire comprising a housing accommodating a plurality of light source parts arranged along a line in a length direction; a light transmissive, optical plate forming part of the housing and extending alongside the light source parts at a distance D, the optical plate having a first and a second face facing towards respectively facing away from the light source parts.

BACKGROUND OF THE INVENTION

Such a luminaire is, for example, known from CN201652175U. In the known luminaire the optical plate is concavely curved towards the light source parts, i.e. light sources, which in the known luminaire are embodied as an array of equidistantly arranged LEDs. The optical plate has a rippled structure on the first surface facing towards the light sources. The rippled structure is embodied as a relatively large, saw-tooth structure, and enhances visual comfort for viewers as it reduces local peaks in the luminance level of light, also called spottiness, as issued through the optical plate to the exterior. Because of the light refractive properties of the rippled structure the point-like light sources are optically enlarged along the line, i.e. in a length direction of the luminaire, and said local peaks in luminance level, caused by the spatial arrangement of the discrete point like light sources, are reduced. Instead that discrete point-like light sources are observed by a viewer, which would be the case if a clear optical plate without rippled structure would be used, in the known luminaire a continuous line of light, however, with a slight fluctuating and relatively low luminance level is observed. A well-known and generally applied alternative to reduce spottiness via refraction, is the use of the effect of scattering by means of a diffusor. This results in "mat optics" with diffuse appearance.

However, a disadvantage of these known luminaires is that their performance in energy efficacy is relatively low, for example for a luminaire with a scattering diffusor typically 50% of the clear optics figures. Another disadvantage of the known luminaire is that the generation of different beam patterns is relatively limited. WO2011071125 discloses a lighting device comprising a line of light sources in a housing closed with an optical plate, said optical plate being provided with a rippled structure, the rippled structure being an undulation with a periodic pattern solely extending along the line.

OBJECT AND SUMMARY OF THE INVENTION

It is an object of the invention to provide a luminaire of the type as described in the opening paragraph in which at least one of the abovementioned disadvantages is

counteracted. Thereto the optical plate has on its first face and/or its second face a rippled structure, said rippled structure being an uncreased undulation having a periodical pattern with a period length PL in the range of ΙΟΟμιη to 1500μ, said pattern extending solely essentially along the line and having an asymmetric form within one period. Preferably said structure is provided only on the first face. Compared to the known luminaire disclosed in CN201652175U, the same principle of refraction is used to give each light source a larger appearance. Yet the efficacy of the luminaire according to the invention is higher than the efficacy of said known luminaire because of its different rippled structure. Because of the rippled structure being uncreased or "smooth", the average angle between the normal to the first surface of the optical plate and the direction of the incident light rays is smaller than in the case of the typical saw-tooth optical structure of the known luminaire. As the Fresnel reflection at a surface is dependent on the angle of incidence, i.e. the larger the angle between the normal to said surface and the direction of the light ray the higher the Fresnel reflection, and each reflection at said surface involves a loss of light, the smaller average incident angle results in the luminaire of the invention to have a higher energy efficacy.

Uncreased or "smooth" in this context means that there are no abrupt changes in tangents to the surface of the rippled structure or in other words that there is no sharp bend or an instant change in orientation of the surface. Light source parts can, for example, be a pair of electrical contacts or lamp holders or an array of light generators such as LED dies. Light source in this context means a LED die + primary optics, for example an optical dome, or it means a LED die + primary optics + secondary optics (for example a reflector around the LED die + primary optics), the optical plate thus can be considered to form the secondary respectively the third optics.

Surprisingly it appeared that the rippled structure being micro-sized further improves the energy-efficacy of the luminaire and yet significantly reduces the spottiness of the light sources. Instead of about 50% loss when scattering diffusers are used and about 30%> loss with diffusing saw-tooth like refractive structures, with the diffusing structure according to the invention a loss down to at the most about 10% is attained compared to a clear, non- rippled optical plate.

Because the undulation of the rippled structure is uni-directional, i.e. groove- like and only in the direction transverse to the length direction, the visual enlargement of the point-like light sources is attained only in the length direction. Hence, an incident light beam on said rippled structure is essentially only broadened in the length direction and essentially not in a direction transverse to the length direction. Transverse in this context means an angle range of plus 10° to minus 10° with the perpendicular direction of the normal to said length direction.

The asymmetrical form of a single period of the periodic pattern of the undulation enables in a relatively simple manner the generation of a large variety of asymmetrical beam patterns. Yet, symmetrical beam patterns, for example a batwing light distribution, can also be generated by the luminaire of the invention, for example when the luminaire comprises an optical plate which comprises two halves in a mutual mirror orientation with respect to a (virtual) mirror plane which extends perpendicular to the length direction.

An embodiment of the luminaire according to the invention is characterized in that D is in the range of 1cm <= D <= 12 cm, preferably 2cm <=D <= 7cm. These are typical convenient values for LED based luminaires used for the illumination of urban areas.

An embodiment of the luminaire is characterized in that the undulation has a periodic length PL and amplitude A. Conventional shapes of the undulation are a rounded saw-tooth structure or a sinusoidal shape. These types of rippled structures are relatively easy to design and relatively easy to manufacture. Typically favorable results for the energy efficacy of the luminaire are obtained when the undulation has an aspect ratio AR defined by PL / A, with 2 <= AR <= 50, preferably with 5 <= AR <= 20. In particular with these aspect ratios for sine wave shaped undulation, steep sections in the undulation that are too steep are avoided which has a positive effect on limiting Fresnel reflections at the first surface of the optical plate and on (the number of) TIR reflections at the second surface and first surface which involves an enhanced risk on light being guided to the sides of the optical plate and lost. Steep section in this context means that said section extends away at relatively small angles, for example angles less than 50°, with the main beam direction of the light sources, i.e. the direction in which light of the highest intensity is issued by the (Lambertian) light sources. Hence, an embodiment of the luminaire is characterized in that said undulation has a steepest section which is oriented with respect to a local normal of the optical plate at an acute angle at the most 50°, for example at the most 40°.

A mentioned before, the micro-size of the undulation further improves and effect of energy-efficacy of the luminaire in combination with a significant reduction in observed spottiness of the light sources. It appeared that this effect was particularly obtained by an embodiment of the luminaire which is characterized in that PL is in the range of 200μιη <= PL <= 600μιη.

The extent of the virtual enlargement of the discrete light sources is both dependent on the pitch P by which the discrete light sources are arranged and on the aspect ratio AR and periodic length PL of the undulation. It appeared that the desired virtual enlargement is obtained by an embodiment of the luminaire which is characterized in that the light sources are arranged at a mutual pitch P and in that P and PL have a mutual size ratio SR with 10 <= SR <= 1000, preferably with 80 <= SR <= 400.

An embodiment of the luminaire is characterized in that at least the second surface has a macro-faceted shape with minimum size S, with S >= P. In the case S=P, each macro-facet can then be associated with a respective light sources and give an attractive optical effect. In the case macro-facets are applied in luminaires with a ring-shaped optical plate according to a polygon, for example a hexagon or an octagon, each macro-facet can be associated with a respective edge of said polygon and in this way enhance the aesthetic appearance of the luminaire and provide macro-optical effects/patterns on the areas illuminated by the luminaires.

An embodiment of the luminaire according to the invention is characterized in that 0.5cm <= P <= 5cm, preferably 1cm <= P <= 3 cm. If the pitch is smaller than 0.5cm virtual enlargement of the light sources is hardly/not required as from normal observation distances of a few meter the light sources merge into a continuous line already without additional optic plate, but this requires a relatively large number of light sources which often is not very practical. If the pitch is equal or less than 5 cm the fluctuation in illumination levels of the observed light line built up by the discrete light sources in combination with the optical plate is satisfactory, but becomes unacceptably obtrusive and disturbing for a pitch larger than 5 cm. A pitch in the range of 1 cm to 3 cm is experienced as very satisfactory with respect to the abovementioned aspects.

An embodiment of the luminaire according to the invention is characterized in that a dimensional ratio DR is P/D. A practical, suitable and convenient DR is at least 2 and at the most about 4, preferably about 2 to 3. For instance if P is 20mm, then D preferably is about 52mm, and if P is 25mm then D preferably is about 58 mm, DR then is about 2.6 respectively 2.3. With DR being at least 2 the discrete light sources start to merge with each other and an observer will observe a continuous light line, with DR being at the most 4 the luminaire still has convenient physical proportions.

An embodiment of the luminaire according to the invention is characterized in that the optical plate is ring-shaped, preferably a rectangular ring, square ring, hexagonal ring, elliptical ring or circular ring. The line along which the light sources are arranged is considered to be the length direction of the optical plate and then has a similar shape, i.e. is a rectangle, a square, a hexagon, an ellipse or a round circle. These shapes are convenient shapes for optical plates and particularly suitable for luminaires applied in street lighting and lighting in urban areas.

An embodiment of the luminaire according to the invention is characterized in that the optical plate extends with a tilt angle a with respect to a plane, for example a road surface or pedestrian area, with 0°< a <= to 90°, preferably 20° <= a <= 90°. This is of particular relevance for attaining illumination of an area of a substantial dimension in a direction transverse to the length direction.

An embodiment of the luminaire according to the invention is characterized in that the optical plate comprises a concavely curved portion with angle β towards the light source and in a transverse direction, preferably with 0° < β <= 40°, more preferably 5° <= β <= 25°. Apart from possibly positive aesthetic effects of such a curved plate on the attractiveness of the luminaire, the curved form of an optical plate renders the plate to be more rigid and stronger.

The invention further relates to a light transmissive, optical plate suitable for use in the luminaire of the invention and having a mutually opposing first face and a second face, the optical plate having on its first face and/or second face a rippled structure, said rippled structure being an uncreased undulation having a periodical pattern with periodic length in the range of ΙΟΟμιη to 1500μιη, said pattern extending solely essentially along a single direction of the optical plate and having an asymmetric form within one period. An embodiment of the optical plate is characterized in that the undulation has an aspect ratio AR defined by PL / A, with 2 <= PL/A <= 50, preferably with 5 <= PL/A <= 20. This aspect ratio is favorable with respect to minimize Fresnel reflection at the rippled structure.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be further elucidated by means of the schematic drawings, which are not up to scale and in which some features might be exaggerated for the sake of clarity, and in which:

Fig. 1 shows a bird-eye view of a first embodiment of luminaires according to the invention;

Fig. 2 shows a perspective view from below of the luminaire of Fig.1;

Fig. 3A-B show cross-sections of some examples of the undulation of the rippled structure not according to the invention;

Fig. 3C-D show cross-sections of some examples of the undulation of the rippled structure according to the invention;

Fig. 4 shows a partial cross-section of a second embodiment of a luminaire according to the invention;

Fig. 5 shows a partial cross-section of a third embodiment of a luminaire according to the invention;

Fig. 6 shows a cross-section of an optical plate comprising two mirror halves in the length direction.

DESCRIPTION OF EMBODIMENTS

In Fig. 1 shows a first embodiment of some luminaires 1 la,l lb, 1 lc according to the invention arranged in a row along a length direction 3 of a road 1 for illumination of said road defining a horizontal plane P_H. Fig.2 shows a schematic detailed perspective view from below of one luminaire 11 of Fig. 1. The luminaire comprises a housing 112 mounted on a pole 111 , said housing accommodates a plurality of light sources 2, in the figure LEDs with a dome as a primary optics, which LEDs are arranged in a number of rows 9 and within a row at a mutual pitch P, six in the embodiment shown but this could alternatively, for example, be only one row, two, three, ten, or up to thirty rows, along a line 17 in a length direction 7, see Fig. 2, i.e. parallel to the length direction of the road. The housing comprises a rectangular, light transmissive, optical plate 113 and extending alongside the light sources. The optical plate is provided with a micro-sized, rippled structure 10 comprising a smooth undulation 5 (see for example Figs. 3A-D) extending solely essentially transverse to the length direction 7 and which is shown in the Fig.2 for only a small part of the optical plate. Because the undulation of the rippled structure is uni-directional, i.e. groove-like which grooves extend only in the direction transverse to the length direction, the visual enlargement of the point-like light sources is attained only in the length direction 7, i.e. in this case also in the length direction 3 of the road. The emission profile 12a, 12b, 12c of neighboring luminaires generally has some overlap 13a, 13ab, 13bc, 13c to form a continuous, relatively homogeneous illuminated area. Hence, an incident light beam on said rippled structure is essentially only broadened in the length direction 7, i.e. essentially in the C=0 and C=180 planes direction, and essentially not in a direction transverse to the length direction, i.e. in the C=90 and C=270 planes direction (see Fig. 2). The optic plate causes the light issued by the light sources to be homogeneously distributed on the road and that the observation by a viewer of spottiness of the light sources is counteracted. The optical plate is flat and is not tilted with an angle a with respect to the plane P_H of the road surface, i.e. C-gamma or γ = 90° or in other words a=0°.

Fig. 3A-D show cross-sections of some examples of the undulation 5 of the rippled structure 10 . Fig. 3 A shows a sine-wave form undulation not according to the invention. The undulation has a periodic length PL of about 280μιη and amplitude A of about 28μιη, hence an aspect ratio AR of 10. The undulation of Fig.3B is according to a rounded regular saw-tooth structure not according to the invention. The undulation has a periodic length PL of about 420μιη and amplitude A of about 30 μιη, hence an aspect ratio AR of about 14. Fig. 3C shows a cross-section profile of an undulation according to the invention and which is associated with a respective discrete light source 2 and in which the aspect ratio AR is maximal directly opposite the discrete light source. PL is constant but the amplitude is gradually decreasing from Am (maximum amplitude) to Ad (decreased amplitude) and in a direction towards the side, until it borders the undulation associated with an adjacent light source. Fig. 3D shows an asymmetric smooth undulation for a luminaire which is designed to issue an asymmetric beam profile. The PL and A have an AR of about 4.

Fig. 4 shows a cross-sectional view of a second embodiment of a luminaire 11 according to the invention. The luminaire has a housing 112 mounted on a pole 111 and comprises a single row of light sources 2, in the figure LEDs with a dome as a primary optics and a reflector 16 as a secondary optics, the LEDs issuing light source light 4. The housing further comprises a hexagonal, ring shaped optical plate 113 mounted at a distance D of about 50mm from the light sources. The optical plate here forms the third optics and is provided with the six facets 14 (only one is visible in cross section) corresponding with the hexagon shape of the optical plate and has a rippled structure 10 on both its first surface 6 facing towards the light source and on its second surface 8 facing away from the light source. The optical plate is made from a light transmissive material, for example PMMA, polycarbonate or glass, said optical plate is flat and is tilted by an angle a = 25° with respect to a plane P_H, for example a road surface, i.e. C-gamma or γ = 65°.

Fig. 5 shows a cross-sectional view of a third embodiment of a luminaire 11 according to the invention comprising a housing 112 mounted on a pole 111. The housing accommodates along a circular line a single row of light sources 2 issuing light source light 4 and a circular, ring shaped optical plate 113 as part of the housing. The optical plate is provided with the rippled structure 10 on only its first surface 6 facing towards the light source, at least the second surface 8 facing away from the light source, but essentially the whole optical plate, is curved by an angle β = 9°. The optical plate is tilted on average by an angle α ~ 16° with respect to a horizontal plane P_H. The maximum tilt angle a for this optical plate is about twice the average a and is about 32°.

Fig. 6 shows a perspective cross-section of a central part of an optical plate 113 according to the invention. The optical plate has a first surface 6 and an opposed second, flat surface 8. The first surface is provided with an undulation 5 of a rippled structure 10. The undulation has an asymmetric form within one periodic length PL, the asymmetric form extends in a direction along the length direction 7, or line 17 of light sources. The optical plate comprises two halves 114,115 which are mirrorly arranged on either side of (virtual) mirror plane M. In the embodiment shown, the amplitude of the undulation is constant, alternatively, this amplitude may gradually increase or decrease in the length direction from the center to edges of the optical plate (similar to what is shown in Fig. 3C for each single light source). Yet in another embodiment, the orientation of the asymmetric form is constant over the whole optical plate, the amplitude of the undulation may be constant over the whole optical plate but alternatively may gradually decrease in the length direction from one edge of the optical plate to the opposed edge of the optical plate.

Claims

CLAIMS:

1. Luminaire comprising:

a housing accommodating a plurality of light source parts arranged along a line in a length direction;

a light transmissive, optical plate forming part of the housing and extending alongside the light source parts at a distance D, the optical plate having a first and a second face facing towards respectively facing away from the light source parts,

the optical plate having on its first face and/or its second face a rippled structure, said rippled structure being an uncreased undulation having a periodical pattern with a period length PL in the range of ΙΟΟμιη to 1500μιη, said pattern extending solely essentially along the line and having an asymmetric form within one period, preferably said structure is provided only on the first face.

2. A luminaire as claimed in claim 1 , characterized in that D is in the range of 1 cm <= D <= 12 cm, preferably 2 cm <= D <= 7 cm.

3. A luminaire as claimed in claim 1 or 2, characterized in that said undulation has a steepest section which is oriented with respect to a local normal of the optical plate at an acute angle at the most 50°.

4. A luminaire as claimed in claim 1, 2 or 3, characterized in that the undulation has an aspect ratio AR defined by PL / A, with 2 <= PL/A <= 50, preferably with 5 <= PL/A <= 20, with A being an amplitude of the undulation.

5. A luminaire as claimed in claim 1, 2, 3 or 4, characterized in that PL is in the range of 200μιη <= PL <= 600μιη.

6. A luminaire as claimed in claim 1, 2, 3, 4 or 5, characterized in that the light sources are arranged at a mutual pitch P and in that P and PL have a mutual size ratio SR with 10 <= SR <= 1000, preferably with 80 <= SR <= 400.

7. A luminaire as claimed in claim 6, characterized in that 0.5 cm <= P <= 5 cm, preferably 1cm <= P <= 3 cm.

8. A luminaire as claimed in claim 6, or 7, characterized in that a dimensional ratio DR is P/D with 2 <= DR <= 4, preferably about 2 <= DR <= 3.

9. A luminaire as claimed in any one of the preceding claims, characterized in that the optical plate is ring-shaped, preferably a rectangular ring, square ring, hexagonal ring, elliptical ring or circular ring.

10. A luminaire as claimed in any one of the preceding claims, characterized in that the optical plate extends with a tilt angle a with respect to a plane, with 0° < a <= to 90°, preferably 20° <= a <= 90°.

11. A luminaire as claimed in any one of the preceding claims, characterized in that the optical plate comprises a concavely curved portion with angle β towards the light source parts and in a transverse direction, preferably with 0° < β <= 40°, more preferably 5° <= β <= 25°.

12. A luminaire as claimed in any one of the preceding claims, characterized in that the optical plate comprises two halves, said two halves are oriented as mirror parts on either side of a virtual mirror plane perpendicularly oriented to the length direction.

13. A light transmissive, optical plate suitable for use in a luminaire as claimed in any one of claims 1 to 12 and having a mutually opposing first face and a second face, the optical plate having on its first face and/or second face a rippled structure, said rippled structure being an uncreased undulation having a periodical pattern with a period length PL in the range of ΙΟΟμιη to 1500μιη, said pattern extending solely essentially along a single direction of the optical plate and having an asymmetric form within one period, preferably said structure is provided only on the first face.

14. An optical plate as claimed in claim 13, characterized in that the undulation has an aspect ratio AR defined by PL / A, with 2 <= PL/A <= 50, preferably with 5 <= PL/A <= 20.