GB2507763A

GB2507763A - LED lighting device for back illuminating sign

Info

Publication number: GB2507763A
Application number: GB201220139A
Authority: GB
Inventors: Howard Julian Matthews
Original assignee: Individual
Current assignee: Individual
Priority date: 2012-11-08
Filing date: 2012-11-08
Publication date: 2014-05-14
Also published as: GB201220139D0

Abstract

An LED lighting device 1 for illuminating display panels 12 for signage or and advertising comprises a light strip 1 that, in use, is mounted along a first side of a display panel 12 to direct LED light on to the display panel 12 such that a region adjacent a second opposing side of the display panel to the light guide is illuminated. The light strip is preferably formed as a reflective channel that reflects and shields light A, B so that only the region of the display distant from the light strip is illuminated. By providing light strips on opposite sides of the display an even illumination of the whole display panel is achieved. The channel may be formed with partition walls. The display is preferably in the form of a double-sided lightbox advertising sign for a bus shelter.

Description

LED LIGHTING DEVICE

Field of the Invention

The present invention relates to the field of LED lighting and in particular the use of LEDs (Light Emitting Diodes) in the illumination of advertising signs such as bus shelter adverts.

Background of the Invention

The illumination of signs such as advertising signs is common place. In the past one popular source of lighting for advertising signs, such as those attached to bus shelters, has been fluorescent tubing or strip lights.

The continued rise in energy costs has driven the search for alternative solutions for illuminating advertising signs, which are typically operated for extended periods of time during the hours of darkness.

Advances in LED (light emitting diode) technology have led to its use as an alternative to fluorescent tubing due to lower energy requirements of LEDs and their longer lifespan. LEDs differ from fluorescent tubing in that provide a point light source rather than diffused lighting. This can lead to the undesirable creation of areas of over illumination (i.e. hot spots) and areas of shadow on a sign.

One approach to LED lighting used in slim advertising signs is a light sheet. A light sheet is essentially a sheet of acrylic, etched with a grid-work of grooves, which has LEDs shining into grid-work from the edges of the sheet. Although light sheets provide homogeneous illumination, they are expensive to manufacture, difficult to install and are not suitable for double sided adverting signs.

Another form of LED lighting used in slim advertising signs is the side emitting LED. Side emitting LED unit essentially consist of a pair of parallel plates with an array of several LEDs placed between them. The parallel plates direct the light of the LEDs to shine sideways through 360 and illuminate the sign. The limited number of LEDs provided within each side emitting LED unit requires that the units must be distributed across the area behind the display panel of the advertising sign. Consequently, side emitting LEDs are time consuming to install and are considered an expensive solution for illuminating slim advertising signs such as bus shelter adverts. Furthermore, as with light sheets, current side emitting LEDs designs are not suitable for illuminating double sided advertising signs.

It is also known to make use of LEDs in combination with a lens that serves to magnify and direct the light onto a sign. Such arrangements are once again considered too expensive to make them suitable for wide spread adoption in advertising signs such as bus shelter adverts. In addition, using a lens fails to provide adequate lighting levels at the centre of an advertising sign, whilst still creating hot spots and shadows.

Summary of the Invention

The present invention seeks to provide an alternative LED lighting solution that is suitable for use in the illumination of both single and double sided signs. In addition the solution provided by the present invention is economical to manufacture and install, thus making it an attractive alternative lighting solution for bus shelter adverts in particular.

The present invention provides an LED lighting device for illuminating display panels of the kind used in the sign and advertising industry, said device comprising a light guide that, in use, is mounted along a first side of a display panel to direct LED light on to the display panel such that a region adjacent a second opposing side of the display panel to the light guide is illuminated.

Whilst it is envisaged that the lighting device of the present invention is particularly suited to illuminating rectangular display panels, other shapes of display panel might also be illuminated using the device of the present invention.

The lighting device of the present invention addresses the problem of hot spots and shadowing on the display panel by directing the LED light across the display panel rather than directly at it.

In particular by directing the LED light from one side of the display panel to illuminate a region of the display panel located on the opposite side of the display panel, thus leaving the region of the display panel adjacent to the lighting device un-illuminated by the lighting device, the occurrence of over illuminated areas (i.e. hot spots) and shadowing is reduced thereby giving a must uniform illumination of the display panel.

Preferably the illuminated region may be limited to the 70-80% of the display panel located closest to the opposite side of the display panel to the light guide. Further preferably the lighting device may illuminate the 3!4s of the display panel located furthest from the lighting device whilst the 1/4 of the display located closest to the lighting device is not illuminated by the lighting device.

Preferably the light guide may comprise an elongate housing for a plurality of LED light sources and whereby the housing has two side walls and an opening through which the LED light is directed on to the display panel.

Further preferably the elongate housing may have at least one partition wall located between the two side walls and acting with the side walls to direct the LED light towards the display panel.

The elongate housing may comprise a main partition wall, which runs substantially parallel to the side walls, and a plurality of secondary partition walls, which run between the side walls.

When in use and the lighting device is mounted along a vertical edge of a display panel the housing side walls and the main partition wall co-operate to direct and restrict the LED light horizontally, whereas the secondary partition walls co-operate to direct and restrict the LED light vertically.

It is appreciated that the dimensions of the light guide are to a certain extent dependent on the dimensions of the display panel that is to be illuminated and as a consequence it would be unduly limiting to specify exact dimensions (although examples are provided in the description of the preferred embodiment of the invention). However it is considered preferable that the spacing between the side walls and said partition walls may be indirectly proportional to the distance between the first and second sides of the display panel.

Similarly the height of the side walls and said partition walls may preferably be proportional to the distance between the first and second sides of the display panel.

In embodiments of the present invention that have partition walls it is considered preferable that each partition formed within the housing has at least one LED light source.

Another aspect of the present invention provides an advertising sign box having a rectangular display panel on at least one face thereof behind which an advert can be received and wherein an LED lighting device according to the present invention is mounted within the box along a first side of the display panel.

Preferably the advertising sign box may be provided with a second LED lighting device according to the present invention mounted within the box along a second opposing side of the display panel.

By providing two separate lighting devices, each of which illuminates a region of the display panel on the opposite side of the box to the lighting device, it is possible to illuminate the entire display panel whilst minimising the creation of hot spots and shadowing, which can present in bands across the panel.

Preferably each lighting device may be mounted along one of longest sides of the sign box.

Preferably the advertising sign box may be provided with a second rectangular display panel on a second face thereof. In this way the adverts can be displayed on both sides of the sign box (i.e. double-sided).

Preferably the advertising sign box may be a bus shelter advert.

The present invention also provides a method of using LED lighting to illuminate display panels of the kind used in the sign and advertising industry, comprising directing LED light from a first side of a display panel such that it only illuminates a region of the display panel located closest to a second opposing side of the display panel.

By directing the LED light in this manner it is possible to avoid the creation of areas that are over illuminated and bright (i.e. hot spots) and areas of under illumination or shadowing.

Preferably the illuminated region may be limited to the 70-80% of the display panel located closest to the opposite side of the display panel to the lighting device.

Preferably the method may further comprise directing LED light from the second side of the display such that it only illuminates a region of the display panel located closest to the first side of the display panel.

Brief Description of the Drawings

The present invention will now be described by way of the examples shown in the figures, wherein: Figure 1 shows a preferred embodiment of the lighting device of the present invention; Figure 2 shows two lighting devices mounted within an advertising sign box; Figure 3 shows a diagram of way in which the light guide of the present invention restricts and directs the LED light on to the display panel of an advertising sign box.

Detailed Description of the Preferred Embodiments

The LED lighting device of the present invention is considered suitable for illuminating the display panels of a variety of signs, ranging from advertisement signage to road signage.

Upon consideration of the present invention it will be appreciated that the adoption of the lighting device of the present invention will, in addition to giving a uniform illumination of a display panel, provide economic advantages due to the energy efficiency and longer lifespan of LEDs.

By way of example, testing has shown that a fluorescent tube using 256w can be replaced with a LED lighting device of the present invention that uses 92w to produce a luminance greater than lOOcdIm2 (candelas per metre squared) across the whole of the illuminated area. This represents a saving in excess of 60% of the energy used by fluorescent tubes.

The longer operational life of LEDs compared to fluorescent tubing and the ease of installing the lighting device of the present invention also provide economic advantages from a maintenance point of view.

Such advantages are considered to be particularly beneficial in signs that are wide spread and need to be illuminated from dusk until dawn all of the year round, such as road signs and bus shelter advertisements.

For a better appreciation of the present invention a preferred embodiment of the lighting device will be described with reference to the drawings. In addition, and by way of example, the utilisation of the lighting device in a bus shelter advertising sign box will also be described.

The person skilled in the art will, however, appreciate how the LED lighting device of the present invention could be utilised in other forms of signage to provide the above explained benefits.

Figure 1 shows a lighting device 1 according to the present invention. The lighting device is formed from an elongate housing 2. The housing 2 is preferably extruded from aluminium so that the housing acts as a heat sink for the LED light sources (not shown) that are located within the housing. It is envisaged that the housing could be formed from alternative materials without departing from the general concept of the present invention.

Using the housing 2 as a heat sink reduces the possibility of the lighting device 1 overheating, which can be an issue when LEDs are operated continuously for an extended period of time (e.g. in bus shelters or road signs).

The housing 2 has a pair of substantially parallel elongate side walls which run along the length of the housing 2. The side walls are connected to one another by an elongate base wall which also runs along the length of the housing 2. The three walls of the housing thus form a trough or channel within which the LED light sources and the partition walls 3, 4 are received.

Although not shown it is envisaged that an opening may be provided on at least one of the ends of the housing to allow for the LEDs within the housing to be connected to suitable control means and/or a power source.

Located within the space between the elongate side walls of the housing is a main partition wall 3. The main partition wall 3 runs substantially parallel to elongate side walls along the length of the housing 2. Although only one main partition is shown in the preferred embodiment it is appreciated that more that one main partition wall may be provided when illuminating deeper signs for

example.

In addition to the main partition wall 3 there are a plurality of secondary partition walls 4 arranged perpendicular to the elongate walls of the housing at spaced increments along the length of the housing 2.

The spacing of the secondary partitions may be determined by the spacing of the LED light sources, although in arrangements where the partition walls do not extend all the way the elongate base wall this is not essential.

The elongate side walls and the partition walls of the housing act together to restrict and direct the LED light so that the pattern of the light emitted from the housing 2 achieves the required illumination of an associated display panel.

Specifically the side walls and the main partition wall act to restrict and direct the LED light in a plane perpendicular to the walls. Similarly the secondary partition walls act to restrict and direct the LED light in a plane perpendicular to the secondary partitions.

In this way a light device mounted vertically along the side of a display panel will emit LED light that is restricted in both a vertical and a horizontal plane to achieve the required illumination of the display panel.

Whilst the illumination of the display panel will be described in more detail below, it is appreciated that in order to ensure that the lighting device illuminates the necessary region of an associated display panel (i.e. that region located closest to the side of the display panel opposite to the side on which the lighting device is located) the housing 2 and the partition walls 3, 4 must have specific dimensions.

It is understood, for instance, that making distance between the elongate side walls and the main partition wall 3 smaller restricts the spread of the LED light emitted from the housing 2.

Increasing the distance from the LED light source to the housing opening (e.g. by making the side walls and partition walls taller) also restricts the spread of the LED light emitted.

It is therefore also understood that the amount of restriction required to produce a light spread that illuminates the necessary region of an associated display panel can depend on the distance between the first side (where the light device is located) and the opposite side (where the illumination is required) of the display.

Thus a narrower display panel, which has less distance between the first side and the second opposing side, will require a less restricted spread of LED light than a wider display panel, which has a greater distance between the first side and the second opposing side.

The dimensions of the housing 2 shown in the preferred embodiment being described with reference to the drawings are considered suitable for illuminating 4-sheet and 6-sheet signs, which are also known as bus shelter adverts and are typically 1800mm high, 1200mm wide and between 100 to 200mm deep.

It is appreciated that when illuminating for example a bus shelter advert the specific dimensions of light guide made in accordance with the present invention can vary from between 25-45mm wide and 35-55mm high depending on the strength, brighteness and size of the LED light sources being used.

Although not shown in figure 1 it is envisaged that each partition created within the housing is provided with at least one LED light source. Preferably the partition spacing shown in the preferred embodiment will be provided with three LED light sources per partition.

In order to maximise the amount of LED light emitted from the housing both the partition walls 3, 4 and the walls of the housing are preferably coloured white, although silver may also be used in some alternative arrangements.

In order to enable the housing 2 to be mounted adjacent to the display panel 12 that is to be illuminated (see fig. 2), an end cap 5 is secured at either end of the elongate housing 2.

In the preferred embodiment the end cap 5 is secured to the housing 2 by screw fixings that pass through holes 6 in the cap 5. However it will be appreciated that alternative ways of securing the end caps to the housing might be adopted without departing from the present invention.

Each end cap 5 is provided with means to enable the lighting device to be mounted adjacent to a display panel, for example within an advertising sign box 10 as shown in figure 2. The means shown in figure 1 consists of a slot 7 which is engageable with a fixing attached to the sides of a sign box 11.

Alternative fixing means will be readily appreciated.

Preferably, although not essentially, the opening of the lighting device 1 is provided with a transparent covering 8 which encloses the LED light sources within the housing whilst still permitting light exit the housing 2. Enclosing the LEDs in this way protects them against the ingress of water which might cause them to malfunction.

Turning now to figure 2, which shows the lighting device 1 of the present invention mounted, as in use, adjacent to the longer sides of a display panel 12 of an advertising sign box 10. The display panel is mounted within a frame 11.

Preferably the lighting device 1 of the present invention is also secured onto the frame 11. It is appreciated that in order to achieve total illumination of the display panel 12 it is necessary to mount lighting devices on opposing sides of the box 10. Whilst the arrangement shown in figure 2 has a single lighting device 1 on each side it is entirely possible that for larger sign boxes multiple lighting devices could be mounted in series along both sides without departing from the concept of the present invention.

The manner in which an advertising poster is retained in an advertising sign box can vary. However commonly a poster is either sandwiched between two transparent acrylic panels or secured by perimeter clips behind a single transparent acrylic panel. The lighting device of the present invention is considered effective at illuminating both of the above arrangements.

Figure 3 is a diagram to illustrate how the LED light produced by the LEDs located within the lighting device 1, which is mounted along a side of the display panel 12, is restricted and directed so that it only illuminates the 3⁄4 of the display panel located furthest away from the lighting device 1.

Figure 3 is taken from a view looking down upon the advertising sign box 10 of figure 2. However in order to more clearly show what is taking place only a single lighting device 1 is shown.

The sign box 10 has opposing display panels 12 on both of its largest faces and it is here that the image of the sign/advert is located when the sign box is in use.

The box has a width L', which is essentially the distance between a first side of the display panel, on which the lighting device is mounted, and a second opposing side of the display panel, which is to be illuminated by the lighting device.

The lighting device 1 is located on a side wall of the sign box 10 so that it an equal distance from both display panels 12 so that the LED light emitted hits both display panels at the same distance from the lighting device.

As can be appreciated from figure 3 the arrangement of the main partition wall and the LED light sources within the housing causes two separate light spreads to be emitted from the housing.

The narrow light spread A represents the light emitted directly from the LED5 in the housing 1. The wider light spread B, which is more diffuse (i.e. less sharp) than the narrower light spread represents the reflected LED light emitted from the housing 1.

The reflected light spread B first strikes the display panel at a point that is about 1/4 or 25% across the width of box.

The direct light spread A first strikes the display panel furthest from their particular LED light source at a point that is about 1⁄2 or 5Q% across the width ofthebox.

It will be appreciated that if a second lighting device 1 were to be mounted on the opposite side of the display panel to the existing lighting device shown in figure 3 it will be possible to illuminate the entire surface of both display panels. This is considered particularly beneficial for double sided adverts such as are used in bus shelter adverting sign boxes.

Claims

Claims 1. An LED lighting device for illuminating display panels of the kind used in the sign and advertising industry, said device comprising a light guide that, in use, is mounted along a first side of a display panel to direct LED light on to the display panel such that a region adjacent a second opposing side of the display panel to the light guide is illuminated.
2. The device of claim 1, wherein the illuminated region is limited to the 70-80% of the display panel located closest to the opposite side of the display panel to the light guide.
3. The device of claim 1 or 2, wherein the light guide comprises an elongate housing for a plurality of LED light sources and whereby the housing has two side walls and an opening through which the LED light is directed on to the display panel.
4. The device of claim 3, wherein the elongate housing has at least one partition wall located between the two side walls and acting with the side walls to direct the LED light towards the display panel.
5. The device of claim 4, wherein the elongate housing comprises a main partition wall, which runs substantially parallel to the side walls, and a plurality of secondary partition walls, which run between the side walls.
6. The device of claim 3, 4 or 5, wherein the spacing between the side walls and said partition walls is indirectly proportional to the distance between the first and second sides of the display panel.
7. The device of claim 3, 4, 5 or 6, wherein the height of the side walls and said partition walls is proportional to the distance between the first and second sides of the display panel.
8. The device of claim 4, 5, 6 or 7, wherein each partition formed within the housing has at least one LED light source.
9. An advertising sign box having a rectangular display panel on at least one face thereof behind which an advert can be received and wherein an LED lighting device according to any of claims 1 to 8 is mounted within the box along a first side of the display panel.
10. The advertising sign box of claim 9, further comprising a second LED lighting device according to any of claims 1 to 8 mounted within the box along a second opposing side of the display panel.
11. The advertising sign box of claim 9 or 10, wherein the one or more lighting devices are mounted along the longest sides of the sign box.
12. The advertising sign box of claim 9, 10 or 11, wherein the box has a second rectangular display panel on a second face thereof.
13. The advertising sign box of claim 9, 10, 11 or 12, wherein the box is a bus shelter advert.
14. A method of using LEDs to illuminate display panels of the kind used in the sign and advertising industry, comprising directing LED light from a first side of a display panel such that it only illuminates a region of the display panel located closest to a second opposing side of the display panel.
15. The method of claim 14, wherein the illuminated region is limited to the 70-80% of the display panel located closest to the opposite side of the display panel to the lighting device.
16. The method of claim 14 or 15, comprising directing LED light from the second side of the display such that it only illuminates a region of the display panel located closest to the first side of the display panel.