Semiconductor LED lighting continues to improve as it becomes the standard for new and retrofit luminary designs, but the industry faces competition from its organic cousin, the OLED. Universal Display Corporation (UDC), a world leader in phosphorescent OLED (PHOLED) technology, recently demonstrated its flexible transparent Loop Lamp, a ribbon of OLED material that serves as a proof of concept for modern lighting design. According to their press release , “The Loop Lamp is comprised of paper-thin, flexible, shatterproof OLED lighting ‘ribbon’ panels designed into a unique concept chandelier. It is cool to touch and offers a high color rendering index (CRI) that can closely mimic natural sunlight. Manufactured using Universal Display’s single layer UniversalBARRIER® encapsulation technology, the plastic based OLED panels resist exposure to moisture and oxygen, are lightweight and can bend in all directions. The Loop Lamp represents one of many concepts in the application of flexible OLED lighting solutions in home décor, architectural design, art and sculpture.”
I interviewed Dr. Mike Hack, GM of OLED Lighting and Custom Displays and Senior Vice President at Universal Display Corporation, who enlightened me on what’s happening at UDC and what we can expect from the OLED industry in the near future.
What does UDC Do?
Universal Display Corporation began over twenty years ago, working with university research laboratories before eventually setting up its own R&D center. It’s largely a chemical company, creating phosphorescent molecules that can be mass produced by licensed manufacturers.
A PHOLED consists of multiple layers, as shown in the picture above. UDC developed the phosphorescent emitters, which Dr. Hack called “UDC’s secret sauce.” During development, UDC uses a variety of tools to characterize and measure performance. The data is passed along to manufacturers so they can design products based on UDC’s OLEDs, and to UDC’s chemists so they can make improvements in brightness, color, and durability.
UDC provides low-volume quantities of the molecules they develop to chemical manufacturers, who scale up the molecules to commercial volumes, ship them back to UDC who verifies their quality and then ships them to lighting and display manufacturers. Virtually all commercial OLED displays use UDC technology.
The Emissive Layer
Earlier versions of the OLED were fluorescent in nature. Those OLEDs convert about 25% of the incoming electricity to light; the rest is lost as heat. PHOLEDs, on the other hand, convert nearly 100% of the electricity into light. However, that’s only at the molecular level. Unfortunately much of the light gets trapped in the PHOLED material, although UDC is finding ways to improve that. Early PHOLEDs fared about as well as fluorescent OLEDs, allowing only 25% of the light to leave the material. Today that’s up to 40% and it continues to improve.
Efficacy
Efficacy, measured in lumens per watt (lm/W), represents the overall efficiency of a lighting device. Incandescent bulbs have efficacies less than 20 lm/W; fluorescent bulbs do better in the 70 to 100 lm/W range, and semiconductor LED lights lead the pack with over 200 lm/W. PHOLED lights currently sit at around 80 lm/W with 100 lm/W expected by the end of 2015 and up to 150 lm/W expected within five years.
Quality of Light
Although PHOLEDs are lagging behind their semiconductor counterparts in efficacy, PHOLED light is usually considered higher quality. Because semiconductor LEDs are a point source of light, they usually require diffusers to reduce shadows and glare. Diffusers absorb some of the light, reducing the usable light from the bulbs. PHOLEDs are a surface light, not a point source, so they don’t produce harsh shadows or glare, and as such, they don’t need diffusers. All of the light that leaves the PHOLED surface is usable. People who have seen OLED lighting say, “I don’t know what it is, but there’s something about the light that’s remarkable - just the quality of the light.” Scientific studies have shown that lighting has a significant effect on worker productivity, mood, and health. Increased light levels, more natural color temperatures, and reduced glare all contribute to a more productive workforce. This is why energy efficiency isn’t the only consideration when it comes to lighting design.
Color
UDC makes white light using a combination of red, green, and blue emitting material. Although their PHOLEDs produce red and green quite well, a good deep blue PHOLED eludes them for now. Instead they use a lighter blue, which produces a warm white light when combined with red and green. Warm white is good for relaxation, but cool white is preferable for workspaces. As a workaround, UDC makes hybrid OLEDs that use red and green PHOLEDs along with deep blue fluorescent OLEDs, the combination of which produces a cool white that approximates natural daylight. While some light bulbs change their color as they age, PHOLEDs maintain their color spectrum throughout their lives.
A light’s color temperature represents the color spectrum that it emits. Equally important is the color rendering index (CRI), which indicates how accurately a light source reveals the true color of an object, usually relative to natural daylighting. A perfect CRI is 100, which most incandescent bulbs are capable of achieving. Fluorescent bulbs typically have CRIs in the 70 - 90 range. PHOLEDs have a CRI of 90 or better.
Lifespan
All light bulbs gradually dim with use; a bulb’s lifespan indicates how long it will produce at least 70% of its nominal output. Currently PHOLEDs enjoy a lifespan of 20,000 to 50,000 hours, depending on brightness, which is comparable to semiconductor LEDs. Advances in production are expected to increase the lifespan of PHOLEDs.
Stay Cool
Unlike semiconductor LEDS, whose circuitry generates a lot of heat, PHOLEDS are cool to the touch, operating at 5 o C to 10 o C above ambient. This reduces cost and complexity, since the PHOLEDs don’t require a heatsink.
Not the End of Semiconductor LEDs
Although PHOLEDs could take over the space lighting industry, don’t dump your stock in semiconductor LEDs just yet. (Disclaimer: I’m an engineer, not a financial advisor. Don’t take investing advice from me!) LEDs are still the best choice where a point source of light is needed, such as flashlights, headlights, and overhead streetlights.
The Future
UDC is working to advance PHOLED technology. Their current projects include developing a low-cost process of printing PHOLEDs with an inkjet printer, stacking PHOLEDs to improve lifespan, and finding ways to let all of the light that’s produced actually make it out of the PHOLED.
Since OLEDs degrade when exposed to oxygen or moisture, UDC is developing thin-film barriers that are both flexible and transparent, allowing engineers to design a light in whatever shape is needed. Audi and BMW are using these flexible OLEDs for the taillights in some of their concept cars.
Take a Virtual Tour of UDC
As far as space lighting is concerned, PHOLEDs are probably where semiconductor LEDs were a decade ago, which means we could be seeing affordable OLED lights within the next five to ten years.
Images and Video courtesy of UDC