Lighting unit, especially for road illumination

Abstract

A lighting unit comprising a tapering cavity surrounded by a circumferential reflective wall and extending between a light emission window and a light entrance surface where a light source is (to be) mounted. An optical plate having a light outcoupling structure is provided at the light emission window for redirecting and issuing light as a uniform lighting unit light beam. Said uniform lighting unit light beam has a first beam emission angle β in a first direction and optionally, for example for a rectangular shaped light emission window, a second beam emission angle γ in a second direction transverse to the first direction. The tapering cavity having a first cut-off angle α in said first direction, wherein β=α+2*δ with 0°<δ<=10°, and optionally a second cut-off angles ε in the second direction transverse to the first direction wherein γ=ε+Θ with 0°<=Θ<=10°.

Claims

1. A lighting unit comprising: a tapering cavity surrounded by a circumferential reflective wall, the cavity extending between a light entrance surface and a light emission window, the light entrance surface being essentially fully covered or is to be essentially fully covered by a light source; light source holding means provided adjacent or at the light entrance surface for accommodating the light source generating light source light which, during operation, is to be issued into at least a mutually transverse first and a second direction; an optical plate having a light outcoupling structure with micro-sized elements provided at the light emission window for redirecting light source light to be issued as a redistributed lighting unit light beam along an optical axis, said redistributed lighting unit light beam having a beam emission angle R in the first direction, the tapering cavity having a first cut-off angle α in said first direction, wherein β=α+2*δ with 0°<δ<=15°, preferably 1°<=δ<=5°, and with 65°<=β<=165°, the light source has a size S1 in the first direction and the cavity has a height H in the direction along the optical axis, each micro-sized element has a respective dimension Dn in the first direction with 0.01 mm<=Dn<=Dmax, wherein Dmax, H and S1 being mutually related according to H>=3*S1 and Dmax<=1*S1.

2. A lighting unit as claimed in claim 1, wherein in a projection along the optical axis the light emission window and/or the light source has a triangular, square, rectangular, polygonal, round or elliptical form.

3. A lighting unit as claimed in claim 1, wherein the outcoupling structure is facing towards the light entrance surface.

4. A lighting unit as claimed in claim 1, wherein said redistributed lighting unit light beam has a second beam emission angle γ in the second direction transverse to the first direction and the tapering cavity has a second cut-off angle ε in the second direction transverse to the first direction, wherein γ=ε+Θ with 0°<=Θ<=20°, preferably 1°<=Θ<=10°.

5. A lighting unit as claimed in claim 4, wherein ε is in the range of 30°<=ε<=65°.

6. A lighting unit as claimed in claim 1, wherein the lighting unit comprises a light source at the light entrance surface, wherein the light source has a size Sm in a direction in the plane of the light entrance surface and the cavity has a height H in the direction along the optical axis, each micro-sized element having a dimension Dn in a direction transverse to the optical axis with 0.01 mm<=Dn<=Dmax, wherein Dmax, H and S being mutually related according to H>=3*Sm and Dmax<=1*Sm.

7. A lighting unit as claimed in claim 1, wherein the micro-sized elements have a dimension Dn in a direction transverse to the optical axis and a facet height h along the optical axis with 0.01 mm<=Dn<=10 mm and 0.01 mm<=h<=Dn.

8. A lighting unit as claimed in claim 1, wherein the micro-sized elements not directly opposite the light entrance surface have a refractive facet surface facing towards the light entrance surface, preferably said micro-sized elements are in slanted orientation with respect to the optical axis.

9. A lighting unit as claimed in claim 1, wherein the micro-sized elements not directly opposite the light entrance surface have a refractive facet surface facing away from the light entrance surface.

10. A lighting unit as claimed in claim 1, wherein the micro-sized elements directly opposite the light entrance surface have a gable-roof shaped cross-section formed by two refractive facet surfaces facing towards the light entrance surface.

11. A lighting unit as claimed in claim 1, wherein the micro-sized elements are oriented in a slanted/tilted orientation towards the light entrance surface in the first and/or second direction.

12. A lighting unit as claimed in claim 1, wherein the micro-sized elements are separate, discernable entities forming non-continuous lines with each line comprising a number of said entities.

13. A lighting unit as claimed in claim 1, wherein the light entrance surface and the light emission window are mutually tilted at a tilt angle φ, φ being in the range of 0<φ<=30°.

14. A lighting unit as claimed in claim 1, wherein α is in the range of 100°<=α<=160°.

15. A lighting unit as claimed in claim 1, wherein in a projection along the optical axis the light emission window has a rectangular form with a length to depth aspect ratio in a range of 1.5 to 7, preferably in a range of 4 to 5.5.

16. A lighting unit as claimed in claim 1, wherein the lighting unit comprises a built in light source, said built-in light source in projection along the optical axis having a light source length to light source depth aspect ratio in a range of 1.5 to 15, preferably in a range of 3 to 10.

17. A lighting unit as claimed in claim 1, wherein the ratio in surface of the surface of the light emission window and the light source is in the range of 25 to 500.

18. A lighting unit as claimed in claim 1, wherein the light source comprises a pre-built-in array of LEDs or LED-dies.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:

(2) FIG. 1 schematically depicts an application of the lighting unit of the invention for illumination of a road;

(3) FIG. 2 schematically depicts a cross-section in a first direction of a first embodiment of the lighting unit of the invention;

(4) FIG. 3 schematically depicts a cross-section of the lighting unit of FIG. 2 in a second direction;

(5) FIG. 4 schematically depicts a cross-section in a second direction of a second embodiment of the lighting unit according to the invention;

(6) FIG. 5 schematically depicts the relevance of the light source of the lighting unit being a non-point light source;

(7) FIG. 6A-B schematically depicts respectively a perspective view and a top view of an outcoupling structure having a slanted orientation of the micro-sized elements; and

(8) FIG. 7 schematically depicts a line arrangement of micro-sized elements of an outcoupling structure.

(9) The drawings are not necessarily on scale, some parts may be exaggerated in size for the sake of clarity.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(10) FIG. 1 schematically depicts a lighting unit 1 of the invention for illumination of a road 3. The lighting unit is mounted on a pole 5 and has an elliptically shaped light emission window 7, the elliptically shaped light emission window is oriented with its length (or first) direction 9 along the length direction 11 of the road and with its width (or second) direction 13 transverse to the length direction of the road. Thus a specific shape of a lighting unit light beam 14 is generated by the lighting unit rendering an elongated illuminated target area 15 on the road.

(11) FIG. 2 schematically depicts a cross-section in a first, i.e. length, direction 9 of a first embodiment of the lighting unit 1 of the invention. The lighting unit has a cavity 17 surrounded by a circumferential light-reflective wall (or reflector) 19 which extends between a rectangular shaped light emission window 7 and a light entrance surface 21. At or alternatively directly adjacent the light entrance surface a light source 23 is mounted, in the figure a plurality of LEDs mounted on a PCB, having a size S1 in the first direction. In the light emission window an optical plate 25 is provided having an outcoupling structure 27 on an inner/upstream surface 29 facing towards the light entrance surface. In the figure the outcoupling structure is a plurality of prisms 31. The plurality of prisms is symmetrically arranged with respect to the light source and an optical axis 33. The prisms each have a refracting surface 35 and a connecting surface 37 which both render impinging light source light rays 39a,b . . . , to be redirected as lighting unit light rays 41a,b . . . , generally via refraction at the refractive surface and/or via reflection at the connecting surface. Due to the specific symmetrical arrangement of the prisms both the refracted light rays and the reflected rays contribute to the lighting unit light beam without causing glare.

(12) As shown in FIG. 2, the tapering cavity has a first cut-off angle α in said first direction as indicated by non-redirected light rays 39c,d and 41c,d. Hence, α is the angle over which any part of the light source or light entrance surface (if the light source is not yet mounted) is directly visible through the light emission window, or in other words the angle over which the light source/light entrance surface is not fully screened from direct view by the circumferential wall. The lighting unit issues a lighting unit light beam 14, said light beam 14 has a top angle β and most outer light rays 41e,f, wherein β=α+2*δ, δ being the broadening angle by which the cut-off angle α is broadened to become beam top angle β. In the embodiment of FIG. 2 δ is about 6° and α is about 110°.

(13) FIG. 3 schematically depicts mounted on pole 5 a cross-section of the lighting unit 1 of FIG. 2 in a second direction, i.e. width direction 13 of the first embodiment of the lighting unit 1 of the invention. In the light emission window 7 the optical plate 25 is provided having the outcoupling structure 27 on its inner/upstream surface 29 facing towards the light entrance surface 21 where the light source 23 is mounted. The light entrance surface has a size S2 in the second direction, S2 being less or equal to a maximum size Sm of the light entrance surface in any direction in the plane of the light entrance surface. In the figure the outcoupling structure is a plurality of prisms 31 and comprises two groups of prisms. A first group of prisms 45 with a top prism angle μ of, for example, about 140° directly opposite the light source 23 having only refracting surfaces 35 viewed in this cross-section, and a second group of prisms 47 opposite, but not directly opposite, the light source having both a refractive surface 35 and a connecting surface 37 viewed in this cross-section, the top angle of the prisms of the second group being, for example, in a range between about 15° to about 40°. A similar cross section of the outcoupling structure comprising first and second groups is shown in FIG. 2.

(14) As shown in FIG. 3, the tapering cavity 17 has a second cut-off angle ε in said second direction as indicated by non-redirected light rays 39g,h and 41g,h. Hence, ε is the angle over which any part of the light source or light entrance surface (if the light source is not yet mounted) is directly visible through the light emission window, or in other words the angle over which the light source/light entrance surface is not fully screened from direct view by the circumferential wall 19. The lighting unit issues a lighting unit light beam 14, said light beam 14 has a top angle γ in the second direction transverse to the first direction as indicated by most outer light rays 41g,i, wherein γ=ε+Θ, Θ being the broadening angle by which the cut-off angle ε is broadened to become beam top angle γ. In the embodiment of FIG. 3 Θ is about 8°.

(15) FIG. 4 schematically depicts a cross-section in a second direction 13 of a second embodiment of the lighting unit 1 according to the invention as mounted on pole 5. This embodiment of the lighting unit has a light emission window 7 which is in a tilted orientation at a tilting angle φ of, for example 20°, with respect to both the light entrance surface 21 and the light source 23 mounted in the light entrance surface. The inner surface 29 of the optical plate 25 mounted in the light emission window is provided with an outcoupling structure 27 having micro-sized prisms 31. The possibly negative effect of the connecting surfaces 37 of the micro-sized prisms is thus reduced as the direct exposure of the connecting surfaces to the light source is reduced because of the connecting surfaces extending in a more radial direction away from the light entrance surface. The beneficial effect of tilting is affected by height h and width Dn of the micro-sized prisms and the tilting angle φ.

(16) FIG. 5 schematically depicts the relevance of the light source 23 of the lighting unit 1 being a non-point light source, i.e. has a size Sm measured in a direction transverse to the optical axis 33, in the figure Sm is, for example, about 3.5 cm. The lighting unit has a height H along the optical axis, in the figure H is, for example about 12 cm. The light emission window 7 of the lighting unit is provided with an optical plate 25 provided with an outcoupling structure 27 comprising micro-sized elements 31. Each micro-sized element has a respective dimension Dn transverse to the optical axis, only D1 and D2 are shown for two micro-sized elements and typically both being in this embodiment, for example, in a range of about 1 mm to about 5 mm. The angle π.sub.1,2 between light rays directly received on a single micro-sized element from the light source is mainly determined by the size Sm of the light source and the height H of the lighting unit, or to be more precise the distance between the light source and the micro-sized element, and determined to a less degree by the dimension D of the micro-sized element (as long as D<<Sm) and the position of the micro-sized element with respect to the light source (e.g. in a shifted position or positioned directly opposite the light source). To enable sufficiently accurate tweaking/reshaping of the beam via redirection by said micro-sized elements, the angle π.sub.1,2 should be relatively small. If each micro-facet has a dimension D in a range 0.01 mm<=D<=Dmax, and that Dmax, H and Sm are mutually related according to H>=3*Sm and Dmax<=1*Sm, in the figure D=3 mm, the lighting unit with these dimensional restrictions appears to generate sufficiently accurately reshaped/redirected light beams.

(17) Furthermore, analyses have been done on the minimal dimensions for the light emission window when changing the dimension ratios of the light source in the first and second directions. Some aspects that play a role here are:

(18) The amount of light being sufficiently narrow/elongated on the exit window:

(19) The amount of shielding effect of the reflector/circumferential wall for the outcoupling structure being provided on the upstream/inner wall of the optical plate.

(20) Results of these analyses are shown in the table 1 below for a source having a typical area of 900.

(21) TABLE-US-00001 TABLE 1 wX wY H Lx Ly Lx/Ly A.sub.lew/A.sub.ls Intensity level 30 30 120 400 120 3.3 53 Low 30 30 140 665 135 4.9 100 High 45 20 95 440 90 4.9 44 High 60 15 72 330 69 4.8 25 Low 75 12 57 300 55 5.5 18 Low
Wherein: wX is the length of the source in the first direction, i.e. the direction that is along the length direction of the road; wY is the width of the source in the second direction, i.e. the direction that is perpendicular to the length direction of the road; H is the distance between the light source and the light emission window; Lx and Ly are the dimensions of the light emission window in respectively the first and second direction; A.sub.lew/A.sub.ls is the ratio between the surface of the light emission window and the surface of the light source.

(22) Sufficient intensity expresses the possibility of having high intensities at high angles like what is needed for road lighting like ME1. Said high intensity involves that at angles of about 65° an intensity is attained that enables a relatively large pole spacing between adjacent lighting units while maintaining an about equal uniform luminance compared to what is attained with the convention pole spacing using known lighting units. The qualification “low” means it is difficult, and “high” means that there is sufficient intensity available. It is clear that sufficient intensity at high angles is obtained for elongated aspect ratios of the light emission window, for example said ratio Lx/Ly being preferably about 5, in combination with a sufficiently high A.sub.lew/A.sub.ls ratio, for example A.sub.lew/A.sub.ls>=40.

(23) FIG. 6A-B schematically depicts respectively a perspective view and a top view of an optical plate 25 provided with an outcoupling structure 27 having a slanted orientation of the micro-sized elements (prisms) 31. As shown, the micro-sized elements are arranged in columns along the second direction 13 and in rows along the first direction 9. Both the refractive surface 35 and connecting surface 37 of micro-sized elements and their mutual ordering and gradual course in slope are clearly visible.

(24) FIG. 7 schematically depicts a curved line arrangement of micro-sized elements 31 of an outcoupling structure 27 provided on the upstream/inner surface 29 of the optical plate 25. The curves extend more or less in the second direction 13, each curve has respective micro-sized elements with a respective dimension Dn . . . Dn+2 in the first direction. As shown in the figure, the vertical connecting surfaces are smoothened out alongside the first direction 9, their smoothening being depending on their relative position on the optical plate and the position of the light source (not shown).