Flexible white LEDs made from existing tech

A flexible white LED designed with off-the-shelf parts offers uniform light output at high efficiency

A highly-flexible yellow-tinged white-light LED created at National Chiao Tung University in Taiwan combines off-the-shelf parts with novel design patterns. The LEDs produce a uniform sheet of light and could soon find use in curved and flexible TVs and wearable displays.

The device was made from 81 readily-available blue LED chips mounted onto a copper foil, which itself covered a polyimide substrate (a flexible yet rugged material). Atop all this the researchers added a layer of yellow phosphor film coated in polydimethylsiloxane, known as PDMS for short, which is a silicone-based substance known for its stability (inert, non-flammable, and non-toxic), transparency, and flexibility.

This top layer of film turned the light from blue to a warm white-yellow color. The researchers found that the thickness of the silicone between the film and the LED chips determined how much the light was scattered and reflected – too thin relative to the other parts and you could clearly distinguish the individual point sources of light, but get it right and you could have a uniform (or near-uniform) sheet of light.

The flexible LED device reached light output uniformity of 85 percent and light efficiency of 120 lumens per watt, which puts it ahead of standard LED lights such as Philips' US$4.97 8.5-W, 800 lumens bulb. After 1,000 hours of run-time, the device had lost only five percent of its light output. Better yet, the new device continued to output the same amount of light when bent to a curvature with a 1.5 cm radius.

A refined version of the device – or something similar – could make it to market sooner rather than later. As it was designed with off-the-shelf parts, it should not be difficult to produce at volume or to integrate into other existing technologies. It does need more work, however, to reduce its thickness and increase its energy efficiency and lifespan.

A paper describing the research was published in the journal Optics Express.

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