EP2954510B1

EP2954510B1 - Display case

Info

Publication number: EP2954510B1
Application number: EP14712020.8A
Authority: EP
Inventors: Tom LEARMOUTH
Original assignee: Clear Channel International Ltd
Current assignee: Clear Channel International Ltd
Priority date: 2013-02-07
Filing date: 2014-02-06
Publication date: 2023-03-29
Anticipated expiration: 2034-02-06
Also published as: WO2014122462A1; LT2954510T; ES2942686T3; PL2954510T3; DK2954510T3; GB201302166D0; FI2954510T3; EP2954510A1

Description

This invention relates to a display case for illuminating a display. The invention has particular relevance to the display of poster and LCD signage in situations requiring high intensity illumination such as for outdoor display, particularly in brightly sunlit conditions.
Developments in light emitting diode (LED) technology have seen LEDs introduced into ever more diverse fields of lighting. Recently, there has been growing interest in the use of LEDs for illuminated signage as used for advertising and the like, replacing cold-cathode fluorescent lamps (CCFLs) in display cases (also known as "light boxes"). This has been partly driven by environmental considerations (CCFLs usually contain quantities of potentially harmful mercury), but also by cost (although LEDs may be more expensive initially, overall costs may be lower as they require less maintenance and have longer lifetimes). There is also an aesthetic aspect, as the use of LEDs can produce even illumination (CCFLs often result in uneven illumination or "striping").
LED arrays are used to provide display case illumination by backlighting for both posters (as in paper or plastic film-based layers) and LCD (liquid crystal display) display panels.
Typically, LED backlighting of posters is only used in the evening and night-time to shine through the poster to allow the image to be seen. During daylight the LED backlight is off and the image is seen by daylight reflection from the poster front surface.
LED backlights for LCD displays are always on, only varied in intensity to always shine through the LCD matrix. Typical display front-face illumination levels are 2000 candela per square metre, cd/m² (or nits) brightness during direct sunlight and around 300 nits in evening and night time. Automatic dimming may be used to graduate the level of illumination between the two extremes.
There are however issues with the use of LEDs for high intensity illumination, such as required for outdoor displays where it is generally accepted an illumination of at least 1200 nits or higher is required at the display front-face to maintain good readability in sunlight; preferably, a level of 2000 nits should be available to counteract sun brightness peaks.
While achieving this level of illumination is rarely an issue with posters, which generally have good light transmission and daytime reflection, it can be problematic for outdoor LCD digital signage (also known as "Digital Out-Of-Home" or DOOH signage), since unlike with posters typically only about 8% to 12% of the light is transmitted through an LCD panel.
The usual solution is to use large numbers of high-intensity LED backlights (recent developments in LED technology have yielded higher brightness devices) arranged in a closely-packed array located directly behind the LCD panel to ensure good optical coupling. For a standard "six-sheet" or 72-inch poster of 1200 × 1800 mm, as many as 30,000 LEDs may be used.
However, the associated heat dissipation when the LEDs are packed together in large numbers in this way can become problematic. For a display as described above the LED backlight can typically generate approximately 1.5 kW, and when combined with the incident power of direct sunlight of approximately 1 kW/m² this can overheat the LCD panel. This can cause "solar clearing", wherein if the temperature of a high brightness LCD panel exceeds a "clearing temperature" the liquid crystal cells undergo a change in structure (eg. from nematic into isotropic states) which results in the LCD panel becoming entirely black. This typically occurs at temperatures above 60°C, 80°C, 85°C or up to 110°C, dependent on manufacturer.
Current systems generally address this issue with active cooling systems, for example using fans to circulate air over the LED backlight devices, transferring the heat via a heat exchanger to create an ambient airflow. In some such systems a closed-loop air flow is used to ensure no 'dirty' air comes into contact with the LED devices or optical surfaces inside the digital sign. Other systems use liquid cooling.
The heat exchanger and backlight assembly are consequently heavy and bulky (the display described above is typically supplied as an integrated cassette weighing up to 250kg) - which can make them difficult to install and making certain arrangements, such as double-sided units, difficult to realize.
Cooling systems are also expensive, constituting a high percentage of digital sign cost; complete integrated digital signs can cost £30,000 of which 70% of that can be the cost of the air management system.
WO2011/159097A2 and US2013/0083559A1 relate to a detachable light emitting device comprising light emitting diode modules. US2010/027255A1 relates to a light box apparatus comprising at least one light source, a frame, and a light guide plate.
The present invention aims to address at least some of these issues.
According to an aspect of the invention there is provided a display case for illuminating a display, comprising: a frame, for holding the display, the frame having a metal structure; an illumination module mounted at or in a side-limb of the frame and positioned in an air gap; and a diffuser located between the illumination module and the display such that the illumination module illuminates the inner-facing surface of the diffuser; wherein the illumination module is in thermal communication with at least a part of the metal structure of the frame, and the frame is in thermal communication with the external ambient environment.
By having the illumination module in thermal communication with at least a part of the case frame or body the frame may act as a heat sink for the illumination module, thereby enhancing cooling - preferably passive cooling, without requiring moving parts - of the illumination module. The frame may conduct heat from the illumination module, reducing the propensity for a local hot spot to develop in the vicinity of the illumination module. The frame may also dissipate heat into the external ambient environment. As used herein, parts described as being in thermal communication is not limited to those parts being in direct physical contact.
Further aspects of the invention are described by any accompanying claims.
Preferably, the illumination module is mounted at or in a side-limb of the frame. Preferably, the side-limb is in thermal communication with the remainder of the frame.
Preferably, the illumination module comprises at least one LED emitter, preferably a plurality of LED emitters. In some embodiments, the light source may be fluorescent. Other types of light sources may also be used.
Preferably, frame is adapted to hold the display physically separate from the illumination module.
Preferably, the display case further comprises a reflector, adapted to reflect light from the illumination module onto the display.
Preferably, the display case further comprises at least one lens, adapted to redirect the light from the illumination module onto the display. The lens may be adjustable.
Preferably, the display case further comprises at least one diffuser, adapted to diffuse light emitted by the illumination module onto the display.
Preferably, the display case further comprises a polarising light filter adapted to polarise light emitted by the illumination module onto the display.
Preferably, the display case further comprises a window adapted to protect the display. There may be a solar rejection film adhered to the inner facing surface of the window. The window may be attached to the display case by means of an Italian or concealed hinge.
Preferably, the display case further includes the display. The display may comprise a poster. Alternatively, the display may comprise an LCD display panel.
Preferably, the display case further comprises a window adapted to protect the display and an air gap between the LCD panel front face and the inner surface of the window. Preferably, the air gap is between 5 and 20mm, preferably between 10 and 15mm, more preferably approximately 12mm.
Preferably, the LCD display panel is mechanically strengthened by optically bonding glass to at least one face of the LCD display panel.
Preferably, the display case frame is adapted for holding a further display. Preferably, the display case further comprises for each display a diffuser adapted to diffuse light emitted by the illumination module onto the respective display, wherein at least one diffuser is adapted to act as a reflector to reflect light from the illumination module onto the other diffuser. Preferably, there is a gap between the diffusers.
Preferably, the display case further comprises a protrusion extending along part of the case frame and in thermal communication with the illumination module. The protrusion may extend along a side wall of the case frame, preferably along a substantial portion of a member of the case frame. The protrusion may be an extrusion.
Preferably, the protrusion has a plurality of outwardly extending limbs or fins. The limbs may extend radially.
Preferably, the protrusion includes an outer shroud. The shroud may have a substantially D-shaped cross section. Preferably, the shroud defines a passage for air flow.
Preferably, the display case further comprises an air input located at the top of the display case and an air exhaust located at the bottom of the display case. A protective skirt may be provided at the base of the display case. The display case may be sealed. One or more of such features may prevent or at least reduce the ingestion of dust and dirt into the display case and be particularly useful in emerging markets where street dust is prevalent. This may reduce the contamination of the optical surfaces (the display case window) obscuring the display. Such features may also assist in excluding liquids from the display case, which might otherwise cause humidity and/or condensation inside the display case and result in corrosion.
Preferably, the display case further comprises a fan adapted to drive air through the display case.
The display case as described may be incorporated into an item of street furniture, such as a bus shelter. A plurality of such structures, each containing such a display case, may be controlled remotely, preferably centrally. This may allow for control of the displays and/or their illumination.
The invention extends to methods and/or apparatus substantially as herein described with reference to the accompanying drawings.
Any apparatus feature as described herein may also be provided as a method feature, and vice versa. As used herein, means plus function features may be expressed alternatively in terms of their corresponding structure.
Any feature in one aspect of the invention may be applied to other aspects of the invention, in any appropriate combination. In particular, method aspects may be applied to apparatus aspects, and vice versa. Furthermore, any, some and/or all features in one aspect can be applied to any, some and/or all features in any other aspect, in any appropriate combination.
It should also be appreciated that particular combinations of the various features described and defined in any aspects of the invention can be implemented and/or supplied and/or used independently.
These and other aspects of the invention will become apparent from the following exemplary embodiments that are described with reference to the following figures in which:

Figures 1 and 2 show examples of known CCFL display cases for displaying a display;
Figure 3 shows an example of a known LED backlight display case;
Figure 4 shows an improved display case in accordance with the present invention;
Figure 5 shows an LED module for use with the improved display case;
Figures 6 show examples of the improved display case;
Figure 7 shows an example of a two-sided improved display case;
Figure 8 shows an improved display case with a 'D' - shaped section side-limb;
Figure 9 shows the arrangement of cooling fins within the 'D' - section;
Figure 10 shows the door mount of the display case in more detail; and
Figure 11 shows an example of the improved display case in use.

Existing display cases

Figures 1 and 2 show (in perspective and side elevation cross-section) examples of known (prior art) CCFL display cases for displaying a display.
Figure 1 shows a single-sided display case 10 comprising an integrated case assembly 12 with a parallel array of cold-cathode fluorescent lamps (CCFL) or tubes 14 mounted vertically inside.
A poster 16 is positioned in the display case 10 and arranged so as to be backlit by the CCFL tubes 14. The front of the display case comprises a fixed glass window 18 immediately adjacent the front of the poster 16 to protect the poster (and the interior of the display case) from the elements.
Diffuser sheets, typically made of PMMA - or polymethylmethacrylate, a transparent thermoplastic - may be located between the CCFL tubes 14 and the rear side of the poster 16 to ensure an even illumination.
Figure 2 shows a double-sided display case 20 of broadly similar design to that shown in Figure 1, except adapted to display two posters at a time. Diffusers 22 can be seen located between the CCFL tubes 14 and the posters 16.
As mentioned, there has been growing interest in replacing CCFL-based display cases with ones based on LEDs.
Figure 3 shows (in exploded perspective view) an example of a known LED backlit display case 30, broadly similar to the CCFL poster display cases of Figures 1 and 2, in that it also comprises an integrated outer case assembly (not shown) fronted by a glass window 18 and containing a diffuser - only differing in the presence of a digital LCD panel 36 (instead of poster 16) which is backlit by an LED array 34 (instead of CCFL tubes 14). In order to cool the LED array 34 a large heat exchange unit 38 is conspicuous at the rear of the display case 30.
Display cases 10, 20, 30 are typically provided by a manufacturer as a sealed, integrated unit.

Improved display case

Figure 4 shows an improved display case in accordance with the present invention.
Display case 100 comprises a display case frame 110 adapted to accommodate a plurality of LED illumination modules 130 side- or edge-mounted at or in the inside surface of a side-limb 140 of the display case frame 110. The position of the LED modules 130 is such that they are located behind the display 160, 260 (a poster or LCD display) such that illumination of the display 160, 260 is achieved by side-lighting (rather than direct backlighting). A removable glass window or door 180 is located at the front of the display case to protect the display (and the interior of the display case) from the elements.
Figure 5 shows an LED module for use with the improved display case, including showing how each LED module 130 comprises an array of LED emitter elements 132, each with an associated lens 134, arranged on a mounting plate 136, which is in turn affixed to the inside surface of a side-limb 140 of the display case frame 110. Each LED emitter 132 is packaged according to standard methods on a metallised printed circuit board (PCB) with an aluminium laminate on the rear and an insulating epoxy laminate such as FR-4.
For a standard "six-sheet" or 72-inch poster of 1200 x 1800 mm, typically 100 high-power LEDs are arranged in groups, each group on a mounting plate 136. The LEDs may be arranged on mounting plate 136 linearly, in arrays or randomly.
Generally, high efficiency LEDs are particularly suitable, such as the XT-E series of LED emitters from manufacturer CREE, particularly white light LEDs.
The light from the individual LED emitters 132 is focussed into an oval pattern by the lens 134 placed over each LED emitter 132 to provide an even illumination over the inner-facing surface of a diffuser located between the LED emitter 132 and the poster / LCD panel.
In some embodiments, the LED beams may also be varied in brightness (by varying the power supplied) and/or direction (by varying the lens and/or lens position) in order to take account of differing sun illumination, which may vary during the day and/or season.
Figures 6 show examples (in exploded perspective view) of the improved display case:

Figure 6a shows how for displaying a poster, the poster 160 is simply attached to a diffuser 220 and arranged close to the glass window 180.
Figure 6b shows how for displaying an LCD panel, a polarising light filter 250 is positioned between the diffuser 220 and the LCD panel 260. The LCD panel is optionally mechanically strengthened by optically bonding glass 270 to the front and/or rear face of the LCD display panel. In addition, preferably a solar rejection film 290, comprising a partially mirrored film adapted to reject a portion of incident sunlight infra-red radiation entering the display case, is adhered to the inner facing surface of the glass window. Ideally an air gap 300, of typically 12mm, is provided between the LCD front face and the glass window inner surface, for adequate cooling air flow.

A single-sided light box may also (optionally) be fitted with a reflector plate 320 to the blank side, to reflect light back to the diffuser.
The improved side-lit display case 100 can thus efficiently effectively backlight posters 160 (paper or other material transmitting light), or an LCD panel 260. The display case 100 is particularly suited to outdoor environments where the case needs to be sealed to exclude dust and water, where large format LCD cells are required, such as 70" and above with a high percentage of light transmission.
In the improved side-lit LED display case 100 the LED modules 130 are "thermally arranged" which is to say they are located in such a way as to have good thermal communication or contact between the LED emitters 132 and the metal structure of the display case frame 110 in order to passively dissipate the heat generated during operation and so maintain the LED emitters 132 within their safe operating temperature range.
For LCD displays, the separation of the LED modules 130 - hence the LED emitters 132 - from the LCD display 260 further reduces heating of the LCD cells and therefore further reduces the risk of the LCD display 260 experiencing solar clearing.
The use of side illumination allows both single sided and double-sided structures to be realised. Thus the structure can, with minor alteration, backlight two back-to-back posters or LCD cells, creating a double-sided light box.
Figure 7 shows an example of a two-sided improved display case. The double-sided light box employs two plastic sheet diffusers 220, the diffusers being arranged with a gap 350 between them. The gap 350 allows the incident light from the LED emitters 132 to both be reflected by the diffusers 220, and transmitted as backlight illumination. This allows a good spread of illumination over the whole width and height of the LCD panel 260.

Further enhancements

As described above, the use of LED side-lighting eliminates the direct heating of the LCD panel by the close proximity of backlight; nevertheless, the LED modules still require a thermal path for cooling.
Figure 8 shows an improved display case 100 with further cooling features in the form of side-limb extrusions such as D-shaped (as in cross-section) sections or shrouds 400 attached to the side-limbs 140 of the display case frame 110 of the display case 100. The sections 400 form D-shaped channel enclosures through which air can pass, thereby cooling the structure. Other shaped sections may also be used.
Constraining the air flow in this way prevents contamination of the inside of the sealed structure with dust and/or moisture. Contamination by polluted air may be further reduced by placing the air intakes 402 at the top of the display case and the air exhausts 404 at bottom. Optionally, protective skirt 406 may be provided at the base of the display case 100.
D-sections 400 also provide a safety feature in the event that the operating temperature of the display case, more particularly the side-limbs 140 due to heating by the LED emitters 132, causes the outside surface of the side-limb 140 to become too hot to touch. Preferably, the outer temperature of the display case is kept below 45°C.
The cooling effect may be further enhanced by an array of cooling fins 410 within the D-sections 400 to allow heat exchange with the air flow. The fins 410 may be arranged radially in a fan shape, with their common axis centred on the LED emitters.
In some embodiments, the display case is passively cooled by ambient air circulating freely; in alternatives, air is forced through, for example by fans.
Figure 9 shows (in plan view) the arrangement of cooling fins within the 'D'-section side-limb shroud 400, showing the radial arrangement of fins 410 about the axis of the LED emitters, located behind the lens 134. In some embodiments the fins extend to be in contact with the inner surface of the `D'-section side-limb.
Also shown is an example oval light pattern 450 resulting from the lens 134, showing illumination of the diffuser 220.
Certain further advantages of the display case 100 will be evident to the skilled person, including:

The modular approach described above - of separate components of the display case 100 - results in much lighter individual parts which are therefore far easier to install and replace for maintenance. For example, whereas a standard outdoor LCD unit typically weighs 250kg and needs specialised lifting equipment, the heaviest individual item in the improved modular display case 100 is the LCD panel module 260 which has a typical weight of 20-30kg.
The modular approach also enables component parts to be sourced from different manufacturers, allowing for display cases to be cheaper and/or more easily tailored to requirements.
A further advantage is associated with the ease of LED replacement. This allows for the LEDs to be used in an "overdriven" mode. LED light output tends to decrease with use; typically, after 50,000 hours an LED is only approximately 50-70% as bright as originally. In order to maintain a consistent level of illumination, LEDs would need to be driven at a higher power as they age, which also shortens their lifespan. By enabling easier access to and replacement of the LEDs, the LEDs of display case 100 may be overdriven without concern for replacement difficulties rather than being allowed to dim in time.

Figure 10 shows the door mount of the display case in more detail. In particular, the glass window or door 180 may be mounted on the display case 100 at the case head 401 by means of an "Italian" or concealed hinge 403, wherein the glass door 180 comprises a formation which allows to be hung from the top of (rather than integrated into) the display case 100.
Figure 11 shows an example of the improved display case in use. The display case 100 is an LED backlit LCD display as described above, for which typical product specifications would be as follows:

Digital outdoor 2m² LCD (IP67 for Outdoor use)
Outdoor FSU available in Single Sided Digital with LED or without Backlit Rear Poster
Outdoor Free-Standing Unit (FSU) available in double-sided DigitalSuitable as (bus) Shelter Adbox replacement and free-standing unit FSU.
Cooling is by fans to maintain normal working temperature within the unit.
No air-conditioning is used and no filter element has to be maintained.

FSU: Outdoor: Shelter AdBox or FSU	Power Consumption: Maximum 2000W
Screen Type: TFT LCD Portrait 16:9	Power Consumption: Typical 900-1,500W depending on settings chosen
Screen Size: 72" diagonal, active area 803 x 1428 mm	Voltage: 110 -240 V AC 50HzCurrent: 9 Amps @ 240V
Resolution: FullHD 1920 x 1080 pixels, pixel pitch 0,8mm	Brightness: 2000 nits, LED Backlight
Temperature Range: Operating -20C to +40C RH 20-90%
Dimensions: 1370mm x 263mm x 2345.5mm to finished ground	Temperature Range:
	Storage -20C to +40C RH 5% to 90%
	-20C to +60C RH 5% to50%
Backlit Poster: LED Backlight	Safety Glass; 13,5mm thick Laminated
Screen centre point above ground level = 1301.5mm above finished ground	Load Centre: Remotely located with overcurrent and RCCB trip (30ma Earth Leakage breaker)
Material: Aluminium casing with glass windows, thickness 13,5mm (6mm laminated sheets)	Floor fixing drawing: on request
	Installation Manual: on request
Colour: powder coated, colour Black	Surface Finish: Powder coated
PC: Intel i5 processor based with VPro/AMT	Weight (of display case, total): 300KG
Operating System: Windows 7 or other suitable OS	Connectivity: LAN 1GB
RGBW LCD corner feedback sensor	Remote Alerts/Diagnostics: SNMP Traps
Option: Juniper VPN SSG-5 or other VPN (virtual private network) security platform)	Brightness: Ambient Light Sensor auto-brightness
Option: 3G modem or other, preferably wireless, connectivity unit	Option: Touch-screen
Approvals: EMI/EMC: EN55022 Class A, EN55024,EN61000-3-2, EN61000-3-3, EN50121-4,	Approvals: Safety: EN60950-1CE

It will be understood that the present invention has been described above purely by way of example, and modifications of detail can be made within the scope of the invention.
Reference numerals appearing in the claims are by way of illustration only and shall have no limiting effect on the scope of the claims.

Claims

A display case (100) for illuminating a display (160, 260), comprising:
a frame (110), for holding the display (160, 260), the frame having a metal structure;

an illumination module (130) mounted at or in a side-limb (140) of the frame (110) and positioned in an air gap; and

a diffuser (220) located between the illumination module (130) and the display (160, 260) such that the illumination module (130) illuminates the inner-facing surface of the diffuser;

wherein the illumination module (130) is in thermal communication with at least a part of the metal structure of the frame (110), and the frame (110) is in thermal communication with the external ambient environment.
A display case (100) according to claim 1, wherein the side-limb (140) is in thermal communication with the remainder of the frame (110).
A display case (100) according to any preceding claim, wherein the illumination module (130) comprises at least one LED emitter (132), preferably a plurality of LED emitters (132).
A display case (100) according to any preceding claim, wherein the frame (110) is adapted to hold the display (160, 260) physically separate from the illumination module (130).
A display case (100) according to any preceding claim, further comprising a reflector (320), adapted to reflect light from the illumination module (130) onto the display (160, 260).
A display case (100) according to any preceding claim, further comprising at least one lens (134), adapted to redirect the light from the illumination module (130) onto the display (160, 260), preferably wherein the lens (134) is adjustable.
A display case (100) according to Claim 6, wherein the at least one lens (134) is adapted to focus the light from the illumination module (130) into an oval pattern over the inner-facing surface of the diffuser (220).
A display case (100) according to any preceding claim, wherein the diffuser (220) is adapted to diffuse light emitted by the illumination module (130) onto the display, (160, 260) and/or a polarising light filter (250) adapted to polarise light emitted by the illumination module (130) onto the display (160, 260).
A display case (100) according to any preceding claim, further comprising a window (180) adapted to protect the display (160, 260), preferably further comprising a solar rejection film (290) adhered to the inner facing surface of the window (180), more preferably wherein the window (180) is attached to the display case (100) by means of an Italian or concealed hinge (403).
A display case (100) according to any of the preceding claims, further including the display (160, 260) and/or wherein the display (160, 260) comprises a poster.
A display case (100) according to any of claims 1 to 9, wherein the display (160, 260) comprises an LCD display panel (260), preferably further comprising a window (180) adapted to protect the display (160, 260) and an air gap (300) between the LCD panel front face and the inner surface of the window (180), more preferably wherein the air gap (300) is between 5 and 20mm, preferably between 10 and 15mm, more preferably approximately 12mm, and/or wherein the LCD display panel (260) is mechanically strengthened by optically bonding glass (270) to at least one face of the LCD display panel (260).
A display case (100) according to any preceding claim, wherein the frame (110) is adapted for holding a further display, preferably further comprising for each display a diffuser (220) adapted to diffuse light emitted by the illumination module (130) onto the respective display, wherein at least one diffuser (220) is adapted to act as a reflector to reflect light from the illumination module (130) onto the other diffuser (220), more preferably further comprising a gap (350) between the diffusers.
A display case (100) according to any preceding claim, further comprising a protrusion extending along part of the case frame (110) and in thermal communication with the illumination module (130), preferably wherein at least one of: a) the protrusion extends along a side wall of the case frame (110), b) wherein the protrusion extends along a substantial portion of a member of the case frame (110), c) wherein the protrusion is an extrusion, d) wherein the protrusion has a plurality of outwardly extending limbs or fins (410) preferably wherein the limbs extend radially, e) wherein the protrusion includes an outer shroud (400), preferably wherein the shroud (400) has a substantially D-shaped cross section, and/or wherein the shroud (400) defines a passage for air flow.
A display case (100) according to any preceding claim, further comprising an air input (402) located at the top of the display case (100) and an air exhaust (404) located at the bottom of the display case (100),and/or a fan adapted to drive air through the display case (100).
A structure, such as an item of street furniture, incorporating the display case (100) of any of claims 1 to 14, preferably a plurality of structures and means for controlling said plurality of structures.