EP2751477B1

EP2751477B1 - A display cabinet luminaire with directional illumination

Info

Publication number: EP2751477B1
Application number: EP12759831.6A
Authority: EP
Inventors: Vincent Guenebaut; Tomas HENNESY; Andrew John O'riordan; John O'brien
Original assignee: Nualight Ltd
Current assignee: Nualight Ltd
Priority date: 2011-08-30
Filing date: 2012-08-30
Publication date: 2018-04-25
Anticipated expiration: 2032-08-30
Also published as: WO2013030814A3; WO2013030814A2; EP2751477A2; PL2751477T3; ES2673287T3

Description

INTRODUCTION

Field of the Invention

The invention relates to luminaries having LED light sources.
For retail product illumination it is often desirable to illuminate across a face from a shallow angle. An example is illumination from a vertical frame member of products at the front of a refrigeration cabinet.
Our prior published specification number WO2008047335A1 describes an approach involving a non-uniform lens such as a bifocal lens. While this approach is effective, there is room for improvement in light output efficiency. Also, it is preferable to have a simpler lens for cost and quality control purposes. For example, the lens needs to be pressed with a very fine grating tolerance, and can not be extruded in a high-volume process. Also, because a lens is used to achieve the non-uniform beam directionality there is little scope for providing beam diffusion in order to avoid the visibility of individual point-like emissions from individual LEDs. See also US2005/265019 A1 .
The invention is directed towards providing a luminaire which achieves uniform product illumination across a face from a sharp angle in a manner which is simpler and/or more effective, and/or less expensive, and/or has improved beam directionality, and/or has improved beam diffusion..

SUMMARY OF THE INVENTION

According to the invention, there is provided a luminaire as set out in claim 1.
In one embodiment, said angle is in the range of 95° to 115°. In one embodiment, the reflector is planar.
In one embodiment, the drive circuit is also mounted on the substrate.
In one embodiment, the drive circuit is mounted on the substrate on a side of the reflector opposed to that of the LEDs.
In one embodiment, the drive circuit is distributed along the length of the substrate.
In one embodiment, the substrate comprises a series of interconnected substrate modules.
In one embodiment, the modules include a master module for connection to a power supply and a plurality of slave modules
In one embodiment, the master module includes bi-polarity protection to prevent problems from arising if power is connected in reverse order.
In one embodiment, the distance between the LEDs and the diffuser and the LED pitch are chosen so that a target light intensity output is achieved and individual LEDs are not discernable.
In one embodiment, the distance is in the range of about 15mm to about 30 mm, and the LED pitch is in the range of about 5 mm to about 20 mm.
In one embodiment, the pitch is in the range of 10 mm to 15mm.
In one embodiment, the ratio of a maximum distance between the LEDs and the internal surface of the diffuser and the pitch of the LEDs is in the range of 1.5 to 2.5. Preferably, said ratio is about 2.
In one embodiment, the reflector is supported on a series of supports which are mounted on the substrate. Preferably, the supports retain the lower edge of the reflector separated form the substrate. In one embodiment, the separation distance is in the range of 1mm to 2mm. In one embodiment, the supports are clips.
In one embodiment, the web forming the rear wall has a groove engaging a top edge of the reflector to support it.
In one embodiment, the substrate has a top layer comprising an optically reflective white solder resist.
In another aspect, the invention provides a display cabinet comprising a frame and a goods support adapted to support goods with a front display plane, and a luminaire as defined above in any embodiment mounted on the frame with a plane normal to the substrate at an acute angle to said plane.

DETAILED DESCRIPTION OF THE INVENTION

Brief Description of the Drawings

The invention will be more clearly understood from the following description of some embodiments thereof, given by way of example only with reference to the accompanying drawings in which:-

Fig. 1 is a perspective view of a luminaire of the invention, with an end cap removed to show the internal construction, and Fig. 2 is an end view;
Fig. 3 is a perspective view of the luminaire, with the end caps in place;
Figs. 4 and 5 are circuit diagrams for drive circuits of the luminaire of various embodiments;
Fig. 6 is an end view showing the luminaire with mounting brackets connected; and
Figs. 7 and 8 are a diagram and a plot of the light output pattern for the luminaire.

Description of the Embodiments

Referring to Figs. 1 to 3 a luminaire 1 of the invention comprises an extruded aluminium housing 2. The housing 2 is generally L-shaped, with a web forming a base 3 with an integral platform 4 supporting an LED substrate 5. The latter supports a linear array of LEDs, namely a series of LEDs 6 along a front side, and a drive circuit 7 along part of a rear side.
A planar elongate rectangular reflector 14 is supported on a series of cradles 10 on the substrates 5. Each cradle 10 comprises a pair of aligned clips of Cu material. The top of the reflector 14 has a lip 16 which is turned in the direction over the circuit 7 to engage the housing 2 to be retained securely in place.
The housing 2 also includes a web forming a rear wall 8, so that the housing 2 forms a generally L-shaped configuration in end view. The sides of the housing 2 have grooves 11 and 12 along its extremities. The grooves together receive a diffuser 15 retained in a curved generally quadrant-shaped configuration. The diffuser 15 is of the type of material marketed by Bayer under the name Makrolon ET3227™. The groove 11 also receives the lip 16 of the reflector 14.
The luminaire 1 also has end caps 30 with ledges 31 allowing fitting at any desired length of luminaire.
The reflector 4 is preferably at an obtuse angle to the substrate on the LED side, and in this embodiment the angle is about 100°. This provides comprehensive reflection of light in the space directly above the LEDs, weighting the light emission in this direction. More generally, the angle is preferably in the range of 90° to 130° to the plane of the LEDs, and more preferably in the sub-range of 95° to 115°, and most preferably in the range of 98°to 102°.
The distance between the LEDs 6 and the internal surface of the diffuser 15 varies from about 15 mm to about 26 mm in the direction anti-clockwise as viewed in Fig. 2. This range of distances is chosen, together with the LED 6 pitch (13 mm) and the optical properties of the material, so that the LEDs 6 are not individually visible and so that there is adequate illumination intensity, thereby giving the appearance of a conventional fluorescent tube. In this embodiment the ratio between the maximum distance between the LEDs 6 and the internal surface of the reflector 15 and the LED pitch is about 2, and more generally is preferably in the range of 1.5 to 2.5. It has been found that these values provide for uniform illumination along the length of the luminaire 1. The fact that the luminaire 1 has the reflector 14 very close to the LEDs to provide the weighted directionality means that a diffuser such as the diffuser 15 may be used to ensure the uniformity along the length. This would not be possible if the directionality as seen in end view were being achieved by a non-uniform lens as the optical losses might be too great.
Another advantageous parameter is the distance between the LEDs and the reflector 14. This is preferably less than 1.5 mm and most preferably less than 1.0 mm. This ensures that very little emitted light is reflected at angles close to normal. Most of the light which is emitted in the direction of the reflector 14 is reflected with a very wide angle, "glancing" off the reflector 14 for concentrated emission in the space normal to the substrate.
Also, because the reflector 14 is mounted on the clips 10 it is retained at a consistent distance of about 1mm to 2mm from the substrate, and hence there is little risk of electrical shorts. However, this distance is small enough so that the bottom edge of the reflector 14 is not above the top surfaces of the LEDs 6.
The substrate 5 is multi-layered. The layers in sequence from the top down are:

white, reflective, solder resist;
copper;
dielectric, and
Al sheeting.

This arrangement provides for excellent light reflection from the top surface. Moreover, the combination of conductors and insulators provides an efficient thermal path to the housing 2. This arrangement, together with the fact that the heat-generating drive circuit components and the LEDs 6 are spaced along the length of the luminaire, mean that there is uniformly distributed heat generation, allowing increased power driving without risk of excessive localised heat. In this case the LEDs are rated at 0.25W, but this could be higher.
Referring to Fig. 4 the substrate 5 supporting the drive circuit 7 and the LEDs 6 is in a number of modules which are linearly interconnected along the length of the housing 2. A master or lead module 40 includes bi-polarity protection components 41 for connection of a power source. This module also includes soft start circuitry and an EMI protection filters among the components 41. Each subsequent module 45, referred to as a slave module, only has drive circuit components 42, either with buck boost or boost operation.
The lead module could alternatively be arranged to receive mains AC power.
Each LED board has its own driver, the LED driver uses boost or buck/boost circuitry, and the input voltage can range from 24V to 36V. The length of the luminaire can be extended by adding a new slave board to the end of the last one.
Referring to Fig. 5, there is a parallel grouping of LED boards. A single LED driver board 50 powers a number of LED boards 55. For long luminaries a second or additional one may be used to power slave LED boards. Each slave LED board 55 has a simple power regulator circuit to maintain the same current in all boards.
As shown in Fig. 6 the luminaire 1 may be mounted on longitudinal brackets 70 and end brackets 71. The mounting arrangement is chosen according to the cabinet in which the illumination is required. Typically, the luminaire 1 will be mounted so that it illuminates from a shallow angle of only 5° to 20° to the illuminated plane. This plane may be horizontal or vertical, depending on the type of cabinet.
Due to the arrangement of the LEDs 6 and the reflector 14, if the luminaire 1 is mounted vertically at a side of a retail cabinet with the substrate 5 perpendicular to the plane of the front of the cabinet, there is comprehensive illumination along this plane, even at the end distant from the luminaire. The illumination pattern is shown in Figs. 7 and 8, from which it will be seen that there is a high level of illumination in the direction having a large component normal to the substrate.
The following are advantageous features of the luminaire 1:

Small LED pitch (distance between LEDs).
High ratio distance from LED to diffuser/LED pitch (the minimum distance between the diffuser and the LEDs is twice as big as the distance between LEDs, ensuring a uniform light emission by the diffuser).
Directional lighting with large light output towards the shelves.
Sharp cut-off of light with little spillage of light towards the customer standing in front of the display cabinet.
Diffuse appearance to remove the discrete reflection of the LED light sources.
Asymmetric light to provide a large amount of light going for example downwards, to provide illumination all the way down to the bottom of a vertical case.
Orientation capability to cater for the different case designs

It will be appreciated that the invention achieves uniform illumination across a plane even when a plane normal to the LEDs is at a small acute angle to this illuminated plane. This is achieved without need to provide a complex lens. Also, because the mirror may be manufactured inexpensively to have a very low loss the efficiency is high. Moreover, the manufacturing can be inexpensive and with consistent quality as extrusion processes can be used for both the mirror and the lens. It will also be appreciated that the invention achieves excellent directionality because there is a mirror arranged to apply such directionality before the light passes through the diffuser.
The invention is not limited to the embodiments described but may be varied in construction and detail. For example it is envisaged that the mirror may be of a non-planar shape such as concave parabolic. However, the optical advantages that might be achieved would not justify the additional manufacturing cost compared to a flat, planar mirror. Also, the linear array of LEDs may be a single line as illustrated or alternatively two or more lines, possibly in a staggered arrangement.

Claims

A luminaire comprising:
an elongate housing (2),

an elongate substrate (5) supporting a linear array of LEDs (6),

a diffuser (15) mounted on the housing over the LEDs (6),

characterized in that,

the luminaire further comprises an elongate reflector (14) mounted on the substrate at an angle in the range of 90° to 130° to the substrate on a side of the substrate on which the LEDs (6) are supported,

the distance between the LEDs (6) and the reflector (14) is less than 1.5mm measured along the plane of the substrate;

the diffuser (15) is mounted on the housing over the LEDs (6) and the reflector (14); and

the housing is generally L-shaped, with a web supporting the LED substrate and a web acting as a rear wall, both webs having grooves or ridges (11, 12) along their edges engaging the diffuser.
A luminaire as claimed in claim 1, wherein said angle is in the range of 95° to 115°.
A luminaire as claimed in any of claims 1 or 2, wherein the reflector is planar.
A luminaire as claimed any preceding claim, wherein the drive circuit (7) is mounted on the substrate on a side of the reflector opposed to that of the LEDs.
A luminaire as claimed in any preceding claim, wherein the drive circuit (57) is distributed along the length of the substrate (5), and wherein the substrate (5) comprises a series of interconnected substrate modules; and wherein the modules include a master module (40) for connection to a power supply and a plurality of slave modules; wherein the master module includes bi-polarity protection (41) to prevent problems from arising if power is connected in reverse order.
A luminaire as claimed in any preceding claim, wherein the distance between the LEDs (6) and the diffuser (15) and the LED pitch are chosen so that a target light intensity output is achieved and individual LEDs are not discernable; and wherein the distance is in the range of about 15mm to about 30 mm, and the LED pitch is in the range of about 5 mm to about 20 mm; and wherein the pitch is in the range of 10 mm to 15mm.
A luminaire as claimed in claim 6, wherein the ratio of a maximum distance between the LEDs and the internal surface of the diffuser and the pitch of the LEDs is in the range of 1.5 to 2.5.
A luminaire as claimed in any preceding claim, wherein the reflector (15) is supported on a series of supports (10) which are mounted on the substrate (5); and wherein the supports retain the lower edge of the reflector separated from the substrate.
A luminaire as claimed in claim 8, wherein the separation distance is in the range of 1mm to 2mm.
A luminaire as claimed in either of claims 8 or 9, wherein the supports are clips (10).
A luminaire as claimed in any preceding claim, wherein the web forming the rear wall (8) has a groove (11) engaging a top edge (16) of the reflector to support it.
A luminaire as claimed in any preceding claim, wherein the substrate (5) has a top layer comprising an optically reflective white solder resist.
A display cabinet comprising a frame and a goods support adapted to support goods with a front display plane, and a luminaire (1) of any preceding claim mounted on the frame with a plane normal to the substrate at an acute angle to said plane.