The organic light-emitting diode (OLED) is one of the lighting industry’s most exciting technologies. It offers extraordinary energy-saving potential, while enabling unique user experiences. However, its development is about seven years behind its popular cousin, the LED, and significant technical advances must occur before broader adoption is possible.
The promise of OLED
OLED technology is used as a display technology in small-screen devices, such as cell phones and digital cameras, and it has strong potential for larger applications, such as computers and televisions. It also offers significant promise for illumination.
An OLED lighting device consists of stacked organic (carbon-based) thin films sandwiched between two current-carrying electrodes, which are typically enclosed in plastic or glass. The result is a very thin material that can have a very large area.
The LED is a directional point source. High-power LEDs emit concentrated light from a very small chip, requiring good optical control to prevent glare. In contrast, OLEDs emit soft, diffused light. This could lead to sources that can be stared at directly for long periods of time without the viewer experiencing glare.
As a result, LEDs and OLEDs are complementary technologies. LEDs are ideal for directional lighting applications, such as accent lighting, while OLEDs are potentially well suited for area lighting applications, such as general ambient.
As a diffuse source, OLEDs can be placed closer to the task, meaning they can provide the same light levels with less light output. Hardware used for optical control—such as reflectors, lenses and louvers—is not needed. Because light is emitted in a single direction from the OLED, it is more efficient than using omnidirectional lamps in applications that would be more efficient with directional light, such as wall sconces.
LED operation is highly sensitive to heat buildup inside the LEDs, requiring good thermal management to ensure long, useful life. OLEDs operate cooler and do not require additional heat sinking, which reduces material needs, while allowing OLED devices to contact materials not usually associated with luminaires, such as wood, fabric and plastics. As a result, OLEDs can integrate with architectural materials and surfaces, such as walls and ceilings, windows, furniture and consumer items such as clothing and clothing hangers.
OLED technology further offers the ability for unique form factors and user experiences. It offers the potential to be manufactured or field-cut or curved in custom shapes and patterns. In the future, commercially available OLED products could be transparent in the off state and luminous while on, allowing windows and mirrors to become the luminaires when needed.
State of the art
Current OLED devices are typically configured as panels that can be mounted individually or in assemblies together with housings and drivers that supply low-voltage power and control. These panels may be specified as square, rectangular or round shapes. Square and rectangular are most common. Sizes range up to 36 square inches. They often use the same drivers as LED luminaires, which may provide control capability. Some assemblies require a 24-volt (V) direct current (DC) driver for each panel plus a master 24V DC driver that converts 120V power to lower voltage needed to power the panel drivers.
A typical panel is 4-by-4 inches, approximately 1/16-inch thick and produces up to 200 lumens, with an efficacy of 40–60 lumens per watt (LPW), though efficacy of 80 LPW is predicted within the next year. Brightness ranges from 2,000 to 6,500 candelas per square meter. The light may be monochromatic (single color) or color-tunable using a red, blue and green source mix. Good color rendering can be achieved with color rendering index (CRI) ratings of 80–90. A mix of white light color temperatures is offered from warm (2,700K) to neutral (3,200K) to cool (5,000K). Rated life is currently 10,000 to 15,000 hours (L70), with end-of-life based on lumen depreciation just as with LED products. Currently, there is a tradeoff between life and light output. For example, driving the source to produce 125 lumens shortens life to about 10,000 hours, while driving it at a lower 75 lumens extends it to 15,000 hours.
A number of manufacturers are invested in developing OLED source technology, including GE, LG Chem, Mitsubishi, OLED Works, Osram Sylvania, Philips and others. Manufacturers including Acuity Brands, Blackbody, BlackJack, Novaled, Osram Sylvania, Philips, WAC and Zumtobel have demonstrated OLED luminaire concepts, some of which are offered on the market. OLED products are available as complete luminaires that install similarly to LED luminaires. Well-designed products allow easy replacement of panels as needed. Premade sections of panel systems (such as Philips’ Lumiblade, consisting of plug-connect OLED panels, drivers and supporting components) can also be purchased and matched to a controller for custom applications.
Due to the current higher cost of OLEDs relative to other lighting technologies, the best application of OLEDs at this time is in decorative luminaires, light-art installations, high-end feature spaces and architectural applications that exploit OLEDs’ unique properties.
The Department of Energy’s (DOE) OLED technology road map predicts OLED panels will achieve efficacies as high as 120 LPW with a rated life of 30,000 hours and a cost of $50 per kilolumen by 2020. Jeannine Fisher Wang, P.E., L.C., director, business development and marketing, OLED Business Group, Acuity Brands, said this level of efficiency will be achieved in the next five years. She said that new form factors, material flexibility (most current OLED devices are encapsulated in rigid glass), transparency, and red/blue/green and white color tuning will become available. And cost will fall to $15–25 per kilolumen. Higher light output, longer life and reduced cost, in particular, will enable OLEDs to achieve broader adoption for general lighting.
“Based on feedback we have received from our customers, there is great demand for the application of OLED luminaires where the ability to make a design statement, the overall quality of light, and the experience for users of the space are all of primary importance,” Wang said. “In the near term, we see the greatest opportunity for OLED focused on specialty and high-end spaces due to today’s higher cost relative to other technologies. Clearly, however, we are not looking at OLED as a niche market nor are our global suppliers. As efficacy and price points improve, OLED will become more appropriate for broader lighting applications. In fact, we are looking at OLED applications, which can be positioned at a moderate premium in lighting systems used today, while providing the unique benefits of OLED, including ultra-thin form factors, distinctive designs, efficiency and superior quality of light.”
Technology at a crossroads
Despite their promise, OLEDs face severe challenges in the lighting market as they will seek to go beyond specialty applications and compete against a range of rapidly improving LED products in general lighting applications. LEDs are at about 90–100 LPW and $5 per kilolumen at the package level and $20–$100 per kilolumen at the luminaire level, and they are steadily improving. LED life is at an average of 50,000 hours, and very good products are entering the market for general lighting applications well-suited to OLEDs, such as general ambient lighting for offices and classrooms.
Cost is a major factor, as a large amount of expensive materials is needed to manufacture OLED devices. Manufacturers must precisely achieve uniform layering of material, their thickness measured in nanometers, across substrates with a potentially large area. The substrate itself and the encapsulation barrier are costly components. Despite these daunting challenges, OLED manufacturers anticipate significant reduction in cost as they scale up for high-volume production.
“We expect OLED to be an important part of the lighting conversation but only if the OLED industry works together to advance the technology,” said Jim Brodrick, Ph.D., SSL program manager for the DOE. “The bottom line is that creative approaches are necessary to bring OLED lighting to commercial realization. Barriers need to be addressed as soon as possible, and the OLED lighting industry can learn a great deal from their LED counterparts in how to overcome these.”
As Brodrick suggests, the pace of technological development has been slower than anticipated, which has injected some pessimism into forecasts by analyst firms such as NanoMarkets, which recently published “OLED Lighting Market Forecast 2013,” and IDTechEx Research, which recently published “OLED vs. LED Lighting 2013–2023.”
IDTechEx’s “most likely” forecast puts the OLED market at $1.3 billion in 2023, about 1.3 percent of the market size predicted for LED lighting at that time. NanoMarkets sees a more optimistic $2 billion as possible but only if OLEDs overcome technical and market barriers.
The firm outlined three possible scenarios for the OLED lighting business. In the first, one or two “champion” firms achieve major performance and manufacturing improvements and expand production capacity enough to reduce costs to a level competitive for the general lighting market. If no champion steps forward, costs will stay high and performance will lag, limiting OLEDs to their current specialty application. In the third scenario, the technology fails—not the most likely outcome, according to NanoMarkets, but possible.
Finding its place
OLED lighting is still a young technology. At this time, it offers designers the ability to create signature lighting statements in feature spaces in their projects and solve problems due to this source’s unique characteristics. With OLEDs, they can access unique forms and user experiences that will distinguish a space and its owner. As such, lighting manufacturers will incorporate OLED technology into their products where its value propositions resonate with designers and owners alike.
For OLEDs to achieve broader general lighting application, however, the technology will need to find its markets, communicate its value, and realize performance and manufacturing improvements across the board: in efficacy, service life and cost.
It’s an exciting time in the lighting industry, and we may see OLED technology develop and achieve its place as a complementary technology to LEDs for general lighting over the next five to 10 years.