WO2008155705A1

WO2008155705A1 - Elongated lamp comprising a plurality of leds, and illumination system

Info

Publication number: WO2008155705A1
Application number: PCT/IB2008/052359
Authority: WO
Inventors: Martijn Riemeijer; Denis J. C. Van Oers; Peter A. Wachters
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2007-06-21
Filing date: 2008-06-16
Publication date: 2008-12-24

Abstract

An elongated lamp comprising a plurality of LEDs (21) in only one straight array is described, wherein an elongated lens (23) extends parallel to the array of LEDs (21). The LEDs (21) and the lens (23) have a common longitudinal plane of symmetry. The LEDs (21) are side-emitting LEDs, and the lens (23) comprises, in a cross-section, two convergent parts at opposite sides of the array of LEDs (21).

Description

Elongated lamp comprising a plurality of LEDs, and illumination system

FIELD OF THE INVENTION

The invention relates to an elongated lamp comprising a plurality of LEDs (light-emitting diodes) in only one straight array, wherein an elongated lens extends parallel to the array of LEDs, and the LEDs and the lens have a common longitudinal plane of symmetry. An elongated lens is a lens having a certain predetermined transverse cross- section over a substantial part of its length.

BACKGROUND OF THE INVENTION

Such an elongated lamp is disclosed in EP-A- 1758068. This publication describes a lamp comprising an elongated U-shaped body whose bottom is provided with an array of LEDs. An elongated lens is clamped between the legs of the U-shaped body so as to obtain a beam of light emitted by the lamp.

Lamps comprising a plurality of LEDs can be used as an alternative for conventional light sources and are capable of replacing typical fluorescent and incandescent lamps. A LED can emit a bright light beam, and a lamp comprising a plurality of LEDs can be designed in such a way that its light radiation is similar to the light radiation of a conventional fluorescent or incandescent lamp.

The invention particularly relates to an elongated lamp for illuminating merchandise in a cupboard freezer having a plurality of neighboring transparent doors at its front side. Each door can hinge about a vertical axis, or can shift in its plane in the horizontal direction, so that the merchandise is approachable by a person who opens the door. The elongated lamps are mounted behind the door cheeks, i.e. the vertical posts or jambs along both edges of the doors when the doors are closed. The doors may have a hinged connection with the door cheeks, and, when sliding doors are used, they may slide in front of the door cheeks. The lamps illuminate merchandise behind the doors, with the light beams of the lamps behind two neighboring door cheeks overlapping each other so as to illuminate the merchandise from two sides.

According to the prior art, the merchandise is illuminated by means of tube- like fluorescent lamps mounted behind the door cheeks. The merchandise in the cupboard freezer is then not evenly illuminated, because the part of the merchandise in the central part of the freezer is illuminated to a less intensive extent than the merchandise near the edge of the door.

OBJECT AND SUMMARY OF THE INVENTION

It is an object of the invention to provide an elongated lamp comprising a plurality of LEDs, which lamp can illuminate objects located near the lamp, wherein the intensity of the light radiation can vary in a predetermined manner over the width of the beam, such that the objects closer to the lamp and the objects further away from the lamp are evenly illuminated.

It is another object of the invention to provide an elongated lamp comprising a plurality of LEDs, which lamp can illuminate objects located near the lamp, wherein commercially available LEDs having a specific radiation pattern are used, and wherein the radiation pattern of the lamp deviates in a predetermined manner from the radiation pattern of the LED.

It is a further object of the invention to provide an illumination system for illuminating merchandise in a cupboard freezer having at least one transparent door at its front side and in which the merchandise is evenly illuminated.

To achieve one or more of these objects, the LEDs in the elongated lamp are side-emitting LEDs, wherein the lens comprises, in a cross-section, two convergent parts at opposite sides of the array of LEDs. The expression 'convergent' is herein understood to mean that a light beam passing the convergent part of the lens becomes less divergent.

Side-emitting LEDs are commercially available and are disclosed in, for example, EP-A-1376708. Such a side-emitting LED is integrated with an optical structure, wherein the light radiation is emitted mainly laterally, i.e. substantially in radial directions around the central axis of the LED, and the light radiation generally diverges with respect to a plane perpendicular to said central axis. The two convergent parts of the lens can be connected to each other by means of an additional central part of the lens.

When side-emitting LEDs are arranged in a straight array, an elongated lens at each side of the array can direct the light radiation from the LEDs in a desired direction, and can converge the light beam, i.e. it makes the light beam less divergent, and can furthermore vary the light intensity of the light radiation in dependence upon the angle of the relevant light radiation with respect to a plane perpendicular to the central axes of the LEDs. In a preferred embodiment, the cross-sectional curved shape of the outer surface of the lens is a conic. The curved shape may be a part of a parabola or a circle, but is preferably substantially a part of an ellipse, with the radius of the ellipse decreasing further away from the longitudinal plane of symmetry of the lamp. The outer surface of the lamp thus has no ribs or other unevennesses, so that it has the appearance of a tube-like lamp which can be cleaned easily. Furthermore, the lamp is more robust than, for example, a TL- tube, and it is more compact because a protecting cover is not required.

Although the inner surface of the lens may have any appropriate shape, the inner surface of the lens in a preferred embodiment has a predetermined shape including non- concave portions which, together with the convex curved outer surface of the lens, form the two convergent parts of the lens. The expression 'non-concave' is herein understood to mean substantially flat or convex.

In a preferred embodiment, the LEDs as well as the lens are fixed to an elongated mounting member. The mounting member and the lens, provided with appropriate end portions of the lamp, can form a closed housing for the LEDs.

The distance between every two neighboring LEDs in the array of LEDs is preferably more than 5 cm, preferably between 10 cm and 15 cm. When making use of LEDs having a bright light radiation, such a distance provides an appropriate light radiation emitted by the lamp, i.e. a uniform light radiation throughout the length of the elongated lamp. The invention also relates to an illumination system for illuminating merchandise in a cupboard freezer having at least one transparent door at its front side, wherein elongated lamps as described above are mounted behind the two vertical cheeks of the door, with the light beams of the lamps near both vertical edges of the door overlapping each other. This means that the merchandise in the freezer is illuminated by lamps at both sides of the transparent door.

In a preferred embodiment, the cupboard freezer has a plurality of neighboring transparent doors at its front side, wherein the elongated lamps are mounted behind at least three vertical cheeks of at least two neighboring doors. One elongated lamp then illuminates merchandise behind two neighboring transparent doors.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be elucidated with reference to a description of embodiments of the lamp and its application, in which:

Fig. 1 shows a side-emitting LED and its light radiation through a lens; Fig. 2 is a sectional view of a lamp taken on the line II -II in Fig. 3;

Fig. 3 is a sectional view of the lamp taken on the line IH-III in Fig. 2;

Fig. 4 is a front view of a cupboard freezer; and

Fig. 5 is a sectional view taken on the line V-V in Fig. 4.

DESCRIPTION OF EMBODIMENTS

Fig. 1 shows a side-emitting LED 1 comprising a base 2 and an optical structure 3. The light source 4 of the LED 1 is located in its central part. The major part of the light radiation leaves the LED in lateral directions as indicated by the broken-line arrows in the Figure. A part of the light radiation from the light source 4 leaves the optical structure 3 directly, and another part of the light radiation is reflected by a substantially conical mirror 5 of the optical structure 3 on top of the LED 1.

The side-emitting LED 1 is covered by an elongated lens 6 shown in Fig. 1 in a transverse cross-sectional view. The outer surface 7 of the lens 6 is cylindrical, and the inner surface comprises two flat parts 8. The two flat parts 8 of the inner surface and the cylindrical outer surface 7 form two convergent lens parts 9,10 at opposite sides of the LED 1. The central plane of the elongated lens part 10 is indicated by a dot-and-dash line 11 in Fig. 1. The light radiation from the LED 1 is converged by the lens parts 9,10 and redirected because the light source 4 of the LED 1 is located at a distance from the central plane 11 of the elongated lens part 10. The broken-line arrows 12 and 13 represent radiation coming directly from the light source 4, and the broken- line arrow 14 represents radiation reflected by mirror 5 of the optical structure 3. By choosing an appropriate shape of the inner surfaces 8 of the lens, the direction of the light radiation emitted by the lamp can be adjusted, so that the intensity of the light radiation can vary in a predetermined radiation pattern. Figs. 2 and 3 show schematically a lamp according to the invention. The

Figures show only parts that are relevant for understanding the invention. For example, means for supplying electric power to the LEDs are not shown in the Figures. Fig. 2 is a transverse cross-sectional view of the lamp, and Fig. 3 is a longitudinal cross-sectional view. Only a part of the lamp is represented, including one of the two ends of the lamp. The elongated lamp is provided with a plurality of side-emitting LEDs 21 mounted on a strip-like elongated mounting member 22. An elongated lens 23 is fixed to the mounting member 22, for example, by means of glue. At both ends of the lamp, the mounting member 22 has an upright portion 24, so that the LEDs 21 are located in an elongated, closed housing formed by the mounting member 22 and the lens 23. In the transverse cross-sectional view of Fig. 2, the outer surface 25 of the lens 23 has the shape of half an ellipse, with the radius of curvature of the outer surface 25 decreasing further away from the longitudinal plane of symmetry of the lamp (the dot-and- dash line in Fig. 2). The inner surface of the lens has four flat parts 26,27,28,29 for obtaining, in combination with the curved outer surface 25 of the lens, a predetermined distribution of the intensity of the light radiation emitted by the lamp.

In particular, the elongated lamp can be used for illuminating merchandise in a cupboard freezer, as shown in Figs. 4 and 5. Fig. 4 shows the front side of the freezer, and Fig. 5 is a horizontal sectional view, indicated by the arrows V in Fig. 4. The freezer has a vertical back wall 31 and two vertical sidewalls 32. At its front side, it has four cheeks

33,34,35,36 and three transparent doors 37,38,39 connected to the cheeks by means of hinges 40.

The merchandise 41 inside a typical cupboard freezer is approachable by opening the doors 37,38,39 by means of handles 42, as shown for door 38 in Fig. 5 and indicated by arrow 43. The merchandise 41 is exposed on shelves 44 which are carried by the sidewalls 32 and vertical partition walls 45. The partition walls 45 do not extend to the front side of the cupboard interior, so that the temperature in the cupboard freezer as a whole can be controlled.

According to the invention, a plurality of elongated lamps 46 is mounted on the back of the door cheeks 33,34,35,36. As indicated by arrows 47, the light radiation from the lamps 46 illuminates the merchandise 41 evenly, with the light radiation towards the merchandise 41 in the middle of the shelves 44 being more intensive than the light radiation towards the merchandise 41 nearer to the lamps 46. All merchandise 41, also the merchandise beyond the center of the shelves 44, is thus illuminated from two sides, thereby preventing inconvenient shadows in the cupboard freezer and ensuring optimal horizontal light uniformity. One long lamp 46 may be mounted behind each door cheek 33,34,35,36, but an array of lamps 46 can also be mounted.

The embodiments of the invention described hereinbefore are only examples of an elongated lamp and an illumination system according to the invention. Many other embodiments are possible.

Claims

CLAIMS:

1. An elongated lamp comprising a plurality of LEDs (1,21) in only one straight array, wherein an elongated lens (6;23) extends parallel to the array of LEDs (1,21), and the LEDs (1,21) and the lens (6;23) have a common longitudinal plane of symmetry, characterized in that the LEDs (1,21) are side-emitting LEDs, and in that the lens (6;23) comprises, in a cross-section, two convergent parts (9,10) at opposite sides of the array of LEDs (1,21).

2. A lamp as claimed in claim 1, characterized in that the lens (6;23) has a convex outer surface (7;25).

3. A lamp as claimed in claim 2, characterized in that the cross-sectional curved shape of the outer surface (7;25) of the lens (6;23) is a conic.

4. A lamp as claimed in any one of the preceding claims, characterized in that the inner surface of the lens (6;23) has a predetermined shape including non-concave portions

(8;26,27,28,29) which, together with the convex curved outer surface (7;25) of the lens (6;23), form the two convergent parts (9,10) of the lens (6;23).

5. A lamp as claimed in any one of the preceding claims, characterized in that the LEDs (1,21) as well as the lens (6;23) are fixed to an elongated mounting member(22).

6. A lamp as claimed in any one of the preceding claims, characterized in that the distance between every two neighboring LEDs (1,21) in the array of LEDs (1,21) is more than 5 cm, preferably between 10 cm and 15 cm.

7. An illumination system for illuminating merchandise (41) in a cupboard freezer having at least one transparent door (37,38,39) at its front side, characterized in that elongated lamps (46) according to any one of the preceding claims are mounted behind the two vertical cheeks (33,34,35,36) of the door (37,38,29), with the light beams (47) of the lamps (46) near both vertical edges of the door (37,38,39) overlapping each other.

8. An illumination system as claimed in claim 6 for illuminating merchandise (41) in a cupboard freezer having a plurality of neighboring transparent doors (37,38,39) at its front side, characterized in that elongated lamps (46) according to any one of claims 1 to 5 are mounted behind at least three vertical cheeks (33,34,35,36) of at least two neighboring doors (37,38,39).