Slablight - the world’s largest LED backlight?

For many years, Polymer Optics Limited (POL) has designed and developed compact backlighting and keypad illumination solutions for leading mobile phone manufacturers, with a drive towards high efficiency and low power consumption. These have typically used small chip LEDs to minimize size and maximize product battery life.

To achieve these goals, POL has developed advanced optical design techniques for simulating the illumination systems, as well as laser machining processes to produce light control patterns that enable the light handling to be optimized for best illumination efficiency and evenness.

Figure 1 Building on this expertise, POL has now scaled this technology from backlights with sizes of a few tens of millimeters for mobile phones, to backlights of many meters in size for large LCDs, signage and general illumination applications.

Using high power LEDs, large-area systems can now be made with the same approach of high efficiency for optimum illumination brightness and low power consumption. This has been made possible by developing a special light-input optic to interface between the LEDs and the lightguide panels.

The optic (see figure 1) efficiently collects the light and injects it into the backlight plane with a controlled beam profile. The light input function of the optic is designed to maximize the performance of the light control patterns that are either machined into the lightguide panels, or achieved by molding.

As in the smaller mobile phone backlights, the light control patterns (see figure 2) are designed to control the illumination evenness, and can provide very uniform illumination even with irregularly shaped panels, or where the LED input positions are restricted. Using these techniques, light can be projected along panels of over 3m in length for uniform illumination with the linear LED light inputs placed at the extreme ends of the panels.

Figure 2 As shown in figure 2, the light control pattern, machined into the panel material, is designed so that a uniform amount of light is emitted across the whole panel. The light travels within the panel, and emission occurs when the light reaches the machined marks. The light intensity inside the lightguide is lower towards the center of the panel, so that the marks are positioned closer to each other to ensure an even emission distribution.

The technology used for these large-area backlight systems are patent-applied-for in conjunction with Ambisol Limited, a UK-based signage company which is POL's manufacturing partner. The backlight product is marketed by Ambisol under the name “Slablight”.

Ambisol’s mission is the development and manufacture of low-energy illumination systems, supported by large-scale metal fabrication, electronic design and electrical installation services, to enable various LED-based illumination projects.

Ambisol has manufacturing systems in place for the production of Slablight lightguide panels as large as 3 x 1.2m in a single piece, and these sections can be joined together to make much larger-area installations.

To date, Ambisol/POL have designed, manufactured and installed many illumination systems using Slablight for a variety of applications:

Interior color-changing panels
A color-changing wall has been installed in the central London headquarters of a major film studio (see figure 3).

Figure 3 The wall of light stands 1.4m high with a linear length of 14m. The wall is illuminated on both sides and stands in the large atrium foyer of the building, where, even in high-brightness ambient conditions, the LED color illumination is strong enough to illuminate the surrounding walls and features of the foyer.

However, using POL’s efficient backlighting technology, the color wall is illuminated with a total of only 246 one-watt LEDs per color (red, green and blue). Power consumption is less than 350W per color, or 1100W in total. The system uses a Helvar 900 router which gives the customer complete control over the lighting levels and color mixing.

An infrared remote controller facility was included, along with full programming access over the customer’s LAN network, to give the operation manager complete control of the illumination effects.

Exterior frontage lighting
A large-area installation has been provided to illuminate the atrium of Sainsbury’s supermarket at Team Valley, Newcastle-Upon-Tyne, UK (see figure 4).

Figure 4 The top section of the building’s atrium frontage is clad with 100 square meters of Slablight panels fitted inside the architectural glass. The system is illuminated with a total of 3228 one-watt LEDs which consume a total of 4.5kW and provide an illumination brightness of 50cd/m² (nits).

The LED drivers are housed in thermally monitored cabinets with spare drivers fitted for failure-free operation. Again, the high efficiency of the Slablight LED lightguide technology enables the large LED illuminated area to attain a comparable brightness level to the lower section of the atrium, which is illuminated by MBF incandescent flood lights.

Backlight for advertising billboard
The final example using Slablight is a solar-powered 4 x 3m backlit advertising bill-board development (figure 5).

Figure 5 The bill-board was originally developed using electro-luminescent (EL) illumination to provide a low power consumption of 550W and a slim, low-profile build, but concerns were raised over the life of the EL panels.

Using Slablight, the bill-board is made up of four 3 x 1m panels illuminated with a total of 96 one-watt LEDs with a total power consumption of only 115W. This makes the solar power aspect of the project far more viable, requiring a much smaller area of photovoltaic (PV) solar panels.

A further advantage of the LED system is an increase in the illumination brightness from 25cd/m² (nits) for the EL system to over 50cd/m² for the LED system - twice the brightness with only around one fifth of the power consumption of the EL approach.

The electrical system simply comprises the 24V supply to the LED drivers from four low-cost lead/acid batteries which are charged from three 180W solar panels with a total area of 3 square meters. This gives capacity to run the bill-board for several hours per day and can be extended further with integrated charge management.

This makes these bill-boards ideal for temporary sites, or sites with no mains power supply, since they can be easily transported in their basic 3m x 1m sections, assembled on site, and made operational within a few hours.

Larger LED backlit bill-boards can be made with this very versatile Slablight lightguide system, by assembling a number of smaller section of up to 3 x 1.2m each and with a designed illumination brightness to suit the particular application.