A new light is appearing. Organic light-emitting diodes (OLEDs) stand where LEDs stood about 10 years ago—promising but expensive. But, as LEDs demonstrated, rapid advances can lower cost and speed up adoption. That’s the expectation for OLED lighting.
John W. Curran, president, LED Transformations LLC, said projected market estimates of OLED lighting vary from $58 million to $4.7 billion.
“So does anybody have a clue? I’m not so sure,” Curran said. “What I see are OLEDs making progress with efficacy, better color, longer life and flexible substrates.”
OLEDs are a diffuse-area light source produced in extremely thin sheets. A carbon-based semiconductor layer emits light when electricity is applied by adjacent electrodes. Electric current drives the light’s intensity. Color is determined by the emissive material used (e.g., red, green and blue emitters for white).
As with LEDs, the U.S. Department of Energy (DOE) is working with the lighting industry to develop and commercialize OLEDs.
“When I first started looking at OLEDs in 2010, they averaged 25 lumens per watt,” Curran said. “Today, they average around 90. The DOE projects OLEDs will ultimately achieve 190 per watt (LEDs 250 lumens per watt). Life is still an issue.”
Without a lifetime testing standard in place for OLEDs, the DOE estimates average life of OLED at 40,000 hours, though some have tested as high as 50,000. Light output decreases to 70 percent after average life. Like with LEDs, drivers and other factors affect OLED lifetimes.
While Curran anticipates LEDs will remain dominant in the solid-state lighting (SSL) market due to lower cost and higher light input, he finds OLEDs offer some distinct advantages.
“OLEDs don’t need a heat sink since the heat they generate is spread across the entire surface of the OLED, unlike LEDs that are point sources and highly directional,” he said. “OLEDs also don’t need secondary optics, are nonglare, and, as an area light source, offer soft, uniform light distribution.”
Improving OLED
The DOE’s 2017 Small Business Innovation Research and Small Business Technology Transfer grants for SSL reveal needed breakthroughs for OLED lighting to reach broad commercialization. Grant winner Pixelligent Technologies, based in Baltimore, is a case in point. An optical advanced materials company, Pixelligent is working on better light extraction.
“We are attempting to make a brighter, more efficient OLED device offering smooth, refractive illumination throughout without altering the emissive layers,” said Matt Healy, vice president of product management, Pixelligent Technologies. “In today’s OLED lighting panels, only about 25 percent of the light generated escapes the device as available illumination. A combination of sources are responsible for this loss, including electrical inefficiency and optical effects such as total internal reflection. Pixelligent’s light-extraction technology creates high refractive indices (RI) layers, so internal reflections are eliminated, and the light can travel smoothly offering better efficacy. We hope to better OLED efficacy and, to a lesser degree, its lifetime.”
Healy said his company has been advancing OLED technology for a number of years having won previous grants.
“The first grants allowed us to improve OLED efficiency by 100 percent, which got people’s attention,” he said. “The goal is to create an OLED light device in a commercially relevant form at an attractive or market-acceptable price.”
Pixelligent is working with OLEDWorks LLC, the only U.S.-based OLED manufacturer, and another grant winner. The Rochester, N.Y.-based firm is using Pixelligent’s work to improve the efficiency of its OLED lighting devices, now averaging 80–90 lumens per watt. That puts OLEDWorks in line with the next generation of high-efficiency OLED devices.
“Like LED, there is still an efficiency gain to go,” Healy said. “OLED is still catching up in light output. The goal is 100 lumens per watt, and we have seen how this is possible with our technology.”
“Research is also needed to extend OLED life as well as create moisture-tight seals,” Curran said. “Encapsulation is critical along the edges of the OLED panel, particularly in flexible substrate configurations. Moisture contamination is a killer to the phosphors.”
Pixelligent and OLEDWorks are addressing encapsulation and a novel substrate process through the same DOE grant. If successful, the technologies would allow for a reduction in OLED panel manufacturing cost.
The cost hurdle
Cost remains a major barrier to OLED adoption. According to the DOE, the current price of an OLED panel is in the range of $100–$200 per kilolumen (klm). It projects a marketable cost of around $15 per klm by 2025. Scaling of the manufacturing process will be important to reduce costs.
“Someone has to manufacture enough product to lower the price,” Healy said. “Maybe OLEDs are offered at a price point that is a reasonable premium. Roll printing of OLEDs would be a big help but it’s not the only way to do it. Scale the technology now and folks will migrate to other high-efficiency processes. It’s important to remember OLED is not set up to look like a light bulb, so the path to broad commercial acceptance may be longer.”
In the game
Acuity Brands Lighting, Conyers, Ga., is all in with OLED. It has a portfolio of OLED panel lighting under its Winona brand encompassing ceiling-, wall- and pendant-mount lighting with a color rendering index (CRI) of 85–90. Color temperatures are available in 3,000K, 3,500K and 4,000K. Its Olessence by Peerless Lighting is a state-of-the-art suspended troffer in 4-, 6- and 8-foot lengths.
“It’s a hybrid fixture where LED uplights the ceiling and OLED downlights for a distributed illumination,” said Ron Schimmelpfenning, vice president, Custom Architectural Lighting Solutions, Acuity Brands. “Olessence allows us to offer an OLED mainstream product at a reasonable cost point with LED doing the major lifting.”
The fixture’s OLEDs provide 700 lumens while a choice of LED output includes 3,000, 4,000 and 6,000 lumens, and 3,000K, 3,500K and 4,000K in 80+ and 90+ CRI options.
“OLED is just pure emission of light over the thin surface,” he said. “It’s light you can hold in your hand. Between OLED and LED, one doesn’t replace the other. Each does what it does well. For instance, you wouldn’t use today’s OLEDs for warehouse or sport venue lighting.”
Dealing with drivers
Drivers that run LED lighting can challenge OLEDs.
“Because OLED internal resistance changes over time, constant voltage drivers do not work well with OLEDs [unlike LEDs],” Curran said. “The other type of power supply used with LEDs—constant current—also requires some modifications for use with OLEDs due to internal capacitance differences. Dimmable drivers that incorporate PWM [pulse width modulation] that work fine with LED sources, will shorten the life of an OLED. Ripple (the amount of variation in output) also must be significantly lower for OLED drivers.”
While Acuity Brands has its own OLED-specific drivers, Schimmelpfenning offered this insight.
“Most of the drivers today are programmable,” he said. “So you can set the drive current. If you operate that same driver you must program it for either an LED stream or OLED. That’s key. Single- to three-panel OLED fixtures need a small driver. While we can do it with our product, the OLED market has not become big enough to offer its own drivers.”
A key demo
In February 2017, the DOE’s Gateway program evaluated a number of different OLED luminaires through an on-site demonstration/evaluation at DeJoy, Knauf & Blood LLP in Rochester, N.Y. Acuity Brands’ LED and OLED products were predominant.
OLED luminaires provided office and break areas with needed task lighting and face and room surface lighting, and also served as a decorative element. Gateway report authors said the OLED luminaires provided comfortable luminance levels, acceptable color quality and controllability, and attractive design. OLEDWorks panels were connected to 0–10 volt dimmers and driven by dedicated OLED drivers. Flicker was negligible. The combined lighting load of OLED and LED was 0.6 watts per square foot, reported as “well below the ASHRAE/IES 90.1 2013 maximum allowed lighting power density (Building Area Method) of 0.82 for office spaces.”
Estimating lifetime
While the Illumination Engineering Society (IES) has standards for LED lifetime, none currently exist for OLED. Curran said that also is holding back OLED lighting.
Jeannine Wang, director of Design Partnership for Acuity Brands, doesn’t disagree but had some additional thoughts.
“With respect to lifetime, partly what happened with LEDs is they had very different depreciation curves [from one chip to the next] that affected how they could or should be tested to determine their lifetime,” Wang said. “This variability is what led to the development of IES TM-21. On the other hand, OLEDs have a more predictable depreciation curve, so it is easier to predict lifetime. Therefore, a standard like TM-21 is probably not needed for OLED, although the basic lifetime testing standard [LM-80] needs to evolve to include OLED in its scope. Heat, and its impact on device performance, is less of an issue for OLED.”
Color shifts with OLED are not prevalent.
“Using the TM-30 standard that looks at fidelity and gamut across the whole color space, there is very little difference in color rendering between LED and OLED,” Wang said. “One visible difference is better reds with OLEDs.”
OLEDs also close LED’s “green gap,” Curran said.
“Now is the time for the OLED industry to pull up their sleeves and try out different things [and] introduce this lighting to architects,” Schimmelpfenning said. “We introduced flat-panel OLED fixture designs for Home Depot, including pendants, wall sconces, and ceiling- and flush-mount designs. This is one more step in introducing OLED light to the general public.”
By Jeff Gavin and originally published in Electrical Contractor magazine.