WO2012146316A1

WO2012146316A1 - Led module for a display

Info

Publication number: WO2012146316A1
Application number: PCT/EP2011/058412
Authority: WO
Inventors: Matthijs Meulenbelt
Original assignee: Lux Et Libertas B.V.
Priority date: 2011-04-27
Filing date: 2011-05-24
Publication date: 2012-11-01

Abstract

The invention relates to a LED module for a display device, such as a posterbox, which LED module comprises: -a circuitry board; -a number of LED's arranged on the circuitry board; -a number of lenses to direct the light into substantially a single plane, the lenses being arranged over the LED's and on the mounting circuitry board; wherein the lenses provide a dust-tight cover for the LED's. The invention also relates to a display device, such as a posterbox, comprising: -a housing having at least one translucent display surface and side walls bordering the display surface; and -at least one LED module according to the invention, said at least one LED module being arranged in the housing on a side wall, wherein the plane in which the light is directed by the lenses is parallel to the display surface.

Description

LED module for a display

The invention relates to a LED module for a display device, such as a posterbox, which LED module comprises:

- a circuitry board;

- a number of LED's arranged on the circuitry board;

- a number of lenses to direct the light into

substantially a single plane, the lenses being arranged over the LED's and on the mounting circuitry board;

Such a LED module is known from WO 2007043886. This LED module is used for the internal illumination of display devices such as posterboxes.

The LED modules as described in WO 2007043886 are typically laid out as a bar of usually 5 high power LED's with lenses to establish a light beam having a wide angle in one direction and a narrow angle in the direction perpendicular thereto. Typically, the narrow angle is 4-10° and the wide angle 40-50° .

In most LED modules, commercially available lenses or copies thereof are used, which provide a light beam as described above. Mostly they are a direct functional copy of the lens, described in WO 2007043886. This limits the layout of most modules: To get an illumination pattern that illuminates the window (s) of the display devices evenly enough, the LED's need to be relatively widely spaced apart. Generic value is 12 cm resulting in modules of ca 60 cm length. The lenses are fitted over a single LED. With nowadays' light output, the limitations of the lenses already become apparent in the form of unwanted spot forming on the window of the display device.

The technical lay-out of a LED module according to the prior art is usually a metal core PCB on which the 5 LED's are wired in series and fed by a current control. The operational voltage is usually 24 Volt. The wiring of 5 LED's in series dates back to the time when the LED's needed a forward voltage of close to or a bit over 4 volts. Power supplies are usually rated 12 VDC or 24 VDC .

Therefore, an operational voltage of 24 volts allows for 5 LED's of the nominal 4 volts, which leaves some voltage left for loss in the current control circuit.

Also versions have been made where the second and fourth

LED were eliminated, resulting in a spacing of ca 24 cm. For smaller display devices or to fill left space, also versions with 3 LED's, spaced at ca 12 cm are available. The functional lay-out still is based on 24VDC so these modules can be used on the same power supply. The entire lay-out is identical: A single lens covers a single LED.

Today's LED's have improved both on light output (Lumen) per Watt and on the forward voltage. The forward voltage has dropped considerably to about 3,2 Volt. However, the known LED modules for display devices currently on the market, still use the outdated 5 LED'S layout proposed in WO 2007043886, although the improved LED's are used.

When the modules for internally illuminated display devices came to market, the water tightness and prevention of dust ingress was no subject. Nowadays most modules are required to comply to the Ingress Protection 66 (IP66) standard, which means they need to be virtually watertight and dust free. This is difficult to attain with most of the commercially available lenses, as these generally are arranged above the LED and leave some space between the lens and the LED, such that dust can get between the LED and the lens .

Since some time, lenses are available that were originally intended to use on sea beacons, i.e. LEDIL FLARE. These have even more extreme angles than the above mentioned, typically 6° by sometimes more than 70°. This allows tighter spacing of the LED's which is of great advantage as a smaller module makes it possible to put the module exactly where wanted, to put in more modules in the display device when required and it saves tremendously on production cost as metal core printed circuit board (MCPCB) , which is needed for cooling the high power LED's, is expensive. Also, these lenses can cope with the increased light output of nowadays' LED's with less unwanted spotforming .

It is an object of the invention to provide a LED module, which reduces or eliminates the above mentioned

disadvantages .

This object is achieved with a LED module according to the invention, which is characterized in that the lenses to provide a dust-tight cover for the LED's and/or electronics. The lenses could also cover additional electronics arranged near the LED' s .

By using the lens as a cover for LED's no dust can get between the LED and the lens, which would reduce the light output .

According to the requirement Ingress Protection 66 (IP

66) a device should be designed such that

- Dust must not enter at all; and

- A strong water jet directed at the enclosure from any direction must not have any harmful effects.

By using the lens as a cover, the LED's will be shielded from any water jets, such that the LED's cannot be harmed.

When combining the lenses into a single cover, the limitations of existing lenses could also be eliminated by using lenses that are laid out similarly to the beacon-lenses. This makes it possible to reduce the spacing between the LED's, thus lowering the needed material to make a module which reduces the price and reducing the unwanted spot forming of current lenses and making the lay-out future proof when the light-output of LED's increases again.

The LED module according to the invention may use high power LED's (1 to 5 Watt, currently at the date of filing) or medium power LED's, somewhere in the 0.5 watt region.

The high power LED's would still require a cooling surface, for example MCPCB or a heat sink, whereas the medium power LED's could be cooled with trough holes and large enough areas on the backside of the glass-epoxy PCB .

Also the housing could function as the heat sink. For this embodiment the LED's must be in heat exchanging contact with the housing, for example through the circuitry board.

In a preferred embodiment of the LED module according to the invention, the lenses have a mounting surface for mounting the lens onto the circuitry board, wherein the mounting surface comprises a cavity for accommodating a LED. In this embodiment, the lens can simply be placed over the LED, such that the mounting surface is brought in to contact with the circuitry board. As the lens will contact the circuitry board with the mounting surface, no dust can get to the LED and any water cannot have an harmful effect on the LED.

Preferably, a gasket is arranged between the mounting surface and the circuitry board. This gasket ensures water tightness of the LED lens housing, sealing the LED completely from the environment.

Another embodiment of the LED module according to the invention, further comprises a housing for housing the circuitry board, wherein the housing comprises at least one opening above the lenses.

The opening above the lenses ensures that the light of the LED's, directed by the lenses in to a single plane can exit the housing without any obstructions.

Preferably, the at least one opening in the housing is covered by a translucent or transparent material. This

translucent or transparent material closes the opening the housing, while the light can exit the housing without any substantial obstructions.

In a preferred embodiment of the LED module according to the invention, the edges of the at least one opening extend beyond the top surface of the circuitry board, in view of the light emitting direction of the LED module, in order to shield of any distortions of the light beam.

By having the edges extending beyond the top surface of the circuitry board, distortions of the light beam caused by imperfections in the lens is shielded off by the extending edges. This prevents undesired light spots at the display surface of for example a display device.

In yet another embodiment of the LED module according to the invention electronic components are arranged on the

circuitry board on the side opposite of the side provided with the LED's. Preferably the electronic components are embedded in a filler, like a potting material or a sealant. The potting material ensures that the electronic components are sealed off and comply with IP66 requirements.

In case of a housing, the LED module according to the invention, the potting material fills the space between the side of the circuitry board provided with the electronic components and the housing. Besides sealing off the electronic components, the potting material provides additional strength the the LED module and also provides an attachment of the circuitry board in the housing.

If the housing is embodied as an extrusion profile, which is closed off by lids at the two ends, has the advantage, that the filler, like potting material, can easily be injected after the circuitry board is mounted in the housing, simply by temporarily removing a lid and injecting the filler.

It would also be possible to arrange the electronic components next to the LED's. Then the circuitry board is folded double, such that the electronic components are arranged on the opposite side of the LED's.

In still another embodiment of the LED module according to the invention electronic components are arranged on the circuitry board on the same side as the LED's and wherein the lenses cover the electronic components.

By arranging the electronic components on the same side as the LED's and the lenses, assembly is substantially

simplified .

A very much preferred embodiment of the LED module according to the invention comprises three LED's.

Against the common practice, in which at least five LED's are used in a configuration known from WO 2007043886, it has been proven to be of advantage to use only three LED's in a LED module according to the invention.

With three LED's wired in series, a power supply of only 12 Volts is sufficient. This is more cost effective than a power supply of 24 Volts, typically used in the LED modules according to the prior art.

Light output has increased so dramatically in the last years that three LED's easily provide the amount of light five LED's would three years ago.

The above at least counts for LED's of about 3 Watts energy consumption. Because of the increase of light output, also less powerful LED's could be used to get enough light output per module. These LED's are about as efficient as the high power versions and can be soldered to a glass-epoxy based PCB with enough trough holes to cool them sufficiently. This relieves the necessity for large cooling surfaces, allowing cost price to drop considerably.

As a result, the lenses are arranged in line and more or less abut against each other in a further embodiment of the LED module according to the invention. This also alleviates the need of a white plane between the lenses as found in the prior art to not disturb the mostly used white paint in display devices, used to spread the light. Because the cooling surface can be smaller, the spacing of the LED's can be reduced. Also by using a lens having a wide angle of over 45°, preferably over 70°, the LED's can be placed more closely and still be able to light a

sufficient large surface.

The invention further relates to a display device, such as a posterbox, comprising:

- a housing having at least one translucent display surface and side walls bordering the display surface; and

- at least one LED module according to the invention, said at least one LED module being arranged in the housing on a side wall, wherein the plane in which the light is directed by the lenses is parallel to the display surface.

The single plane light beam of the LED module according to the invention is directed to the side walls of the housing. The light will reflect and disperse on the side walls, providing an even distribution of the light over the display surface of the display device.

An embodiment of the display device according to the invention further comprises a power supply, preferably a 12

Volts power supply, for powering the at least one LED modules.

In a preferred embodiment of the display device according to the invention the inner surface of the side walls are coated with a light diffusive material, such as a matt white paint.

These and other features and advantages of the invention will be elucidated in conjunction with the accompanying

drawings .

Figure 1 shows an embodiment of a LED module according to the invention.

Figure 2 shows a cross sectional view of the LED module according to figure 1.

Figure 3 shows an embodiment of a display device according to the invention.

Figure 4 shows a cross sectional view of a second embodiment of the LED module according to the invention.

Figure 1 shows in perspective view and with cut away portions an embodiment of a LED module 1 according to the invention. The LED module 1 has a housing 2, in which a

circuitry board 3 is arranged.

Three lenses 4 are arranged on the circuitry board 3. As shown in figure 2, the lenses 4 have a mounting surface 5, with which the lenses 4 are attached to the circuitry board 3. The mounting surface 5 is attached to the circuitry board 3 by a gasket or kit 6. Each lens 4 has at the mounting surface 5 a cavity 7 for accommodating a LED 8 attached to the circuitry board 3. The cavity 7 provides a housing for the LED 8 and the gasket or kit 6 ensures that no dust or moist can get to the LED 8.

Electric components 9, 10 are arranged on the opposite side of the circuitry board 3. These electric components 9, 10 could provide a driver for the LED's 8. The electronic

components 9, 10 are embedded in a potting material 17, which fills the space between the circuitry board 3 and the housing 2, such that no dust or moist could get into contact with the components 9, 10.

The lenses 4 direct the light of the LED 8 into a light beam 11 having a narrow angle a, which is preferably about 4-10°.

Figure 3 shows a display device 12 for displaying posters. The display device 12 has a housing 13 with side walls 14 and two display surfaces 15, 16.

Inside of the housing 13, a LED module 1 is arranged providing a light beam 11 with a wide angle β, which is

preferably over 70°. The light beam 11 is directed to the side surfaces 14, where the light will reflect and disperse providing an evenly distributed back lighting for posters, which are placed directly behind the display surface 15, 16.

Figure 4 shows a second embodiment of a LED module 20 according to the invention. The LED module 20 has a housing 21 with a ridge 22. A lens 23 having a flange 24 is positioned on the the ridge 23, such that a closed of cavity 25 is provided.

A circuitry board 26 is arranged in this cavity and carries the LED 27 and electronic components 28, 29. Because the lens 23 is placed on the ridge 23, the lens 23 provides a dust- tight cover for the lens 27.

Claims

1. LED module for a display device, such as a posterbox, which LED module comprises:

- a circuitry board;

- a number of LED's arranged on the circuitry board;

- a number of lenses to direct the light into

characterized in that

the lenses provide a dust-tight cover for the LED's and/or electronics.

2. LED module according to claim 1, wherein the lenses have a mounting surface for mounting the lens onto the circuitry board, wherein the mounting surface comprises a cavity for accommodating a LED.

3. LED module according to claim 2, wherein a gasket is arranged between the mounting surface and the circuitry board.

4. LED module according to any of the preceding claims, further comprising a housing for housing the circuitry board, wherein the housing comprises at least one opening above the lenses .

5. LED module according to claim 4, wherein the at least one opening in the housing is covered by a translucent or transparent material.

6. LED module according to claim 4 or 5, wherein the edges of the at least one opening extend beyond the top surface of the circuitry board, in view of the light emitting direction of the LED module, in order to shield of any distortions of the light beam.

7. LED module according to any of the preceding claims, wherein electronic components are arranged on the circuitry board on the side opposite of the side provided with the LED's.

8. LED module according to claim 7, wherein the electronic components are embedded in a filler, like a potting material or a sealant.

9. LED module according to any of the claims 4-6 and 8, wherein the potting material fills the space between the side of the circuitry board provided with the electronic components and the housing.

10. Led module according to any of the claims 1-5, wherein electronic components are arranged on the circuitry board on the same side as the LED's and wherein the lenses cover the electronic components.

11. LED module according to any of the preceding claims, comprising three LED's.

12. LED module according to any of the preceding claims, wherein the lenses are arranged in line and abut against each other .

13. Display device, such as a posterbox, comprising:

- at least one LED module according to any of the preceding claims, said at least one LED module being arranged in the housing on a side wall, wherein the plane in which the light is directed by the lenses is parallel to the display surface.

14. Display device according to claim 13, further comprising a power supply, preferably a 12 Volts power supply, for powering the at least one LED modules.

15. Display device according to claim 13 or 14, wherein the inner surface of the side walls are coated with a light diffusive material, such as a matt white paint.