OLEDs: The Other Solid-State Lighting Technology

OLEDs: The Other Solid-State Lighting Technology

By Peter Y. Ngai, PE, LC, FIES, Vice President of OLED Lighting, Acuity Brands Lighting

The solid-state lighting market is presently dominated by inorganic light-emitting diodes (LEDs). LEDs have high efficacy and long lifespans and have nearly reached cost parity with traditional forms of lighting.

A relatively new technology has recently entered the commercial sector, though, which has the potential to expand lighting applications in many of the target lighting markets. Invented in the late 1980s, organic light-emitting diodes (OLEDs) are flat light panels. They are “organic” in that the key functional materials are composed of organic compounds—complex carbon-containing molecules.

Images courtesy of Acuity Brands Lighting

The OLED Difference

OLEDs and LEDs are similar in that they are semiconductor light sources. Both are dimmable, and when they switched on electrons are able to recombine with holes and release energy in the form of photons. Neither luminaire contains mercury or other hazardous materials.

This, however, is where the similarities end.

LEDs each come in a tiny chip. They pack a lot of lumens into a focused point source. As such, they can be easily controlled optically. However, because of their intense brightness, they need to be kept away from direct view to prevent intense glare. For this reason, diffusers, lenses, or reflectors are used as shielding. In addition, heat is generated from a very small region, which leads to high temperature and the need for thermal management and heat sinking.

OLEDs, on the other hand, have diffused area sources, creating light that is calm, soft, and comfortable to view. Their ultra-slim form offers excellent visual light quality. OLED panels are available in various shapes: circular, square, rectangular, and others. Moreover, OLED panels can be made flexible. With OLEDs, heat is dissipated though the entire light-emitting area, so they are cool to the touch.

OLED efficacy has advanced tremendously in the last four years. A high CRI (color rendering index) OLED panel of 90 is approximately 80 lumens per watt, and a nominal CRI OLED panel of 82 is around 100 lumens per watt. As for LEDs, the best chip efficacy of a high CRI LED with a junction temperature of 25oC is about 120 lumens per watt. A nominal CRI LED is currently approximately 160 lumens per watt.

While these comparisons are useful benchmarks, relative performance must be considered on the basis of luminaire efficiency. Overall luminaire efficiency depends on driver and electronic efficiency and light loss due to thermal and optical factors. For LEDs, the U.S. Department of Energy reports that there is a 12-percent light loss due to junction temperature raise and another 11-percent loss due to optics. With OLEDs, however, there are no additional efficiency losses to consider, as confirmed by the same report. From here, it can be seen that the efficiency of OLEDs comes sufficiently close to that of LEDs for most lighting applications, and their efficacy is expected to continually increase at a fast pace.

OLEDs Calm, OLEDs Bright

One of the most obvious OLED lighting applications is in the areas of sconce, pathway, and decorative lights. For these, the light source itself is celebrated. It provides visual interest and visible information and orientation.

Secondary optics and heat sinks are not required for OLED luminaires. For most sconce and marker light applications, the brightness of the OLED is less than 2,000 candela per square meter (cd/m2). This drastically increases the lifetime of OLEDs to upwards of 100,000 hours, making it suitable for 24-7 operation.

The minimal luminaire thickness makes it especially appropriate for satisfying legislation requirements such as ADA. Sconces and marker lights are found in almost every kind of commercial setting, from office buildings and hotels to healthcare facilities and public spaces.

OLED brightness is inherently calm and comfortable. They can be viewed directly at close proximity without glare and are cool to the touch. OLEDs are lightweight and thin and do not require bulky accessories. The combination of these unique features makes them ideal for close-to-user applications.

Taking OLEDs to Task

One of OLEDs’ prime applications is task lighting. In fact, because OLEDs are an area source with diffused lighting distribution, they can provide an additional layer of volumetric illumination to the immediate space surrounding a task area. The surrounding layer of light created by OLEDs results in a much more pleasant and inviting environment that enhances clarity, dimensionality, and the appearance of space over and beyond what traditional task lighting can offer.

When coupled with low ambient lighting for circulation and safety, this task-surround-ambient lighting system can deliver effective lighting solutions for offices, libraries, and other spaces where superior lighting quality and energy savings are needed.

As an extension to task lighting, the same principle can be applied to countertop lighting for reception areas or nurses’ stations. OLEDs do not emit radiation in the ultraviolet (UV) region, so their shadow-free, warm, and gentle glowing light are suitable for other close-to-user applications, such as mirror, shelf, and display lighting.

F4_Revel_OLEDOne of the most important OLED lighting applications is in general illumination for offices and other commercial and institutional spaces. OLEDs deliver not only adequate amount of illumination for task performance but also the necessary volumetric illumination to satisfy people’s psychological appetite for brightness. At the same time, OLEDs provide a glare-free visual environment.

As a direct consequence of design freedom, traditional open-space ambient lighting requires that luminaires be laid out in regimented grid-like patterns, such as 10 feet by 10 feet or 8 feet by 8 feet, for visual uniformity. With OLEDs, lighting panels can be regarded as light tiles, which may be arranged in multiples in any form and shape. This gives a designer complete freedom to create lighting layouts as envisioned by the design intent.

Design freedom offers another advantage of OLED lighting in the form of application efficiency. Energy-efficient lighting can be achieved not only by efficient light source alone but also by delivering the right amount of light where it is needed. Without the restriction of regimented grid-like layouts, OLEDs can place light at points where it is needed most, providing tailored lighting delivery. So, for instance, more OLED panels can be placed for high workspace illumination, while in-between walk space would have fewer panels for lower illumination.

A recent development in OLED lighting is to integrate a LED into an OLED luminaire. A good example is in the application of a pendant direct-indirect lighting system. Harvesting the strength of a LED creates a highly effective, widespread distribution of light for the indirect component, while allowing the OLED to deliver to occupants a soft and comfortable light. This hybrid approach also brings the overall efficiency and cost of the lighting system close to that of a pure LED but with the added benefits of an OLED.

Time to Shine

While OLEDs are still more expensive than LEDs, their costs are coming down precipitously. This is similar to what LEDs experienced a couple years ago. In fact, there are already OLED luminaires in the marketplace that have price points close to that of their LED counterparts—a trend that is expected to continue in the foreseeable future.

OLED technology is still in a fast development stage, with exciting advancements expected to reach its ultimate potential. The lighting industry foresees brighter, larger, better-colored, more efficacious, and even longer-lasting panels. Color-tunable and flexible OLED panels are also on the horizon. Farther out, it will be possible to have transparent OLEDs. Basically, the OLED panel will be a light source when lit; when not energized, the panel will be see-through and may be used as a window or skylight.

From an application standpoint, OLEDs will soon be integrated into walls, ceilings, furniture, and appliances. It is even conceivable that OLEDs will be woven into fabrics or carpets. So, while there is no question that the future of OLED is bright, there’s no time like the present to let OLEDs shine.

This piece was originally published in the February 2016 issue of ei, the magazine of the electroindustry.

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