Many people mistakenly believe solid-state lighting (SSL) is just another name for LED, but that’s not quite accurate. There are several other important forms of SSL that lighting professionals need to know more about.

BY DAVID SHILLER

Although LED has gone mainstream as a light source, it is not the only form of solid-state lighting (SSL) available. There are other types of SSL, each with different inherent advantages and benefits for different specialty lighting applications. Here is a quick look at three other forms of SSL, how they work, as well as their strengths and weaknesses.

OLED

The LEDs that we see every day are technically considered “inorganic light-emitting diodes” or ILEDs. Another form of SSL is “organic light-emitting diodes” or OLEDs, which work by sandwiching different layers (“films”) of organic semiconductors to generate light in very diffuse, larger-area sources known as “panels.” The electrical voltage applied across the layers of semiconductors creates molecules with extra electrons in one layer, and molecules missing electrons (“holes”) in an adjoining layer. Where these two layers meet (the “junction”), electrons (negatively charged) and holes (net positive charge) combine to release energy in the form of light.

Most LEDs emit light this way, in a single wavelength or color – typically blue – that is used to excite a phosphor coating, creating white light. By contrast, OLEDs can produce very high-quality white light — without “blue pumping” or phosphors. OLEDs create broad spectrum white light containing much less blue light. This is considered an advantage of OLED, at a time of increasing concerns over high blue light content from LEDs, at night, as a potential disruptor of sleep and overall health. In addition, OLED is also often 90+ CRI.

Here are some other interesting things to know about OLED technology:

  • The large area, diffuse OLED panels significantly reduce glare compared to the intense “dots” in many LED products.
  • OLED is being designed into automobiles, including tail lights and dashboard displays.
  • OLED is a leading technology in the display industry, including the screens of smart phones, such as the iPhone X.
  • OLED televisions are leading in the premium TV category, with new 8K OLED TVs entering the market.
The Rex 2 OLED pendant
 by Nadarra Lighting
Although Acuity Brands, the largest luminaire maker in North America, has been pioneering and selling OLED luminaires for years, the newest forms of OLED include flexible glass substrates enabling curved OLED panels, as well as OLED panels that are transparent when off.

OLED has been held back in the lighting industry by its higher cost in comparison to LED. Many in the OLED industry are expecting breakthroughs in continuous printing of larger-format OLEDs to significantly bring down costs, which could happen in the near future.

The hospitality and high-end residential sectors have already embraced OLED. Bill McDonnell, Founder & CEO of Rochester, N.Y.-based luminaire manufacturer Nadarra Lighting shares, “Nadarra has designed a number of fixtures that leverage the unique, thin, and flexible form factor of OLED into decorative fixtures that are appropriate for the showroom market. Luxury hospitality markets, such as boutique and lifestyle hotels, are starting to understand that lighting is an integral part of hotel design, including the health and wellness traveler.  OLED fixtures can positively impact someone’s circadian rhythm, and their overall well-being.”

McDonnell’s advice for lighting showrooms is:

“Demonstrate creative leadership by becoming an early promoter of OLED decorative fixtures.
Differentiate yourself from other showrooms that do not carry this technology.
Become an expert in all forms of solid-state lighting —LED, OLED, etc. 
Put your showroom on the cutting edge of changing the conversation around light. Showrooms that carry OLED fixtures are changing the way society will view lighting in years to come.”

Sebastian Scherer, CEO of the German lighting fixture manufacturer Neocraft comments, “The main reason we used OLED as a light source for our Iris pendant was that it is quite innovative and an easy way to integrate into the fixture construction. It’s very thin and heat is not a big problem,” he explains. “Another advantage is the glare-free and pleasant luminance. We also decided on OLEDs because you can replace them easily as well as the environmental benefit. Our entire pendant – including the light source – is made in Germany.” Acuity Brands, Nadarra Lighting, and Neocraft all incorporate OLED panels manufactured by OLEDWorks, an American leader in OLED technology.

Laser-Phosphor & Laser Fiber-Optic

Anyone who has exhausted their cat with a laser pointer has experienced Laser Diodes, or LD. The remarkable things about LDs are their minute size and intensity. Most LDs are almost too small to see with the naked eye, and emit light from an area 1/10,000 that of a typical 1mm x 1mm LED. That incredibly small light-emitting surface (or LES) gives laser diodes their most powerful feature: optical control. This can be turned into remarkably tight beam angles as small as 1 degree, as well as sources that can throw more than half a mile!

Just like LEDs, LDs produce light of a single wavelength/color. If blue or violet light is combined with special tough phosphors, this can create safe, white light. Laser diodes use even more complex sandwiches of semiconductors to emit light into a reflective cavity (“optical cavity”) that amplifies the intensity of the light until it escapes from a minute opening.

The intensity and directionality of laser diodes also makes them the perfect light source for fiber optic delivery in either colored or white light. Much like LEDs or OLEDs, LDs create light from the combination of electrons and holes at the junction of semiconductor layers within the LDs. Among the important differences is the fact that many laser diodes produce light that is coherent, stimulated emission, rather than the incoherent, spontaneous emissions of LEDs. This means that within a laser diode, photons of the same frequency, polarization, and phase create more and more photons travelling in the same direction as the first photons. This amplification – or “gain” – gives the LD its intensity, along with the absence of “droop” (the typical drop in LED efficiency as current and temperature increase). By contrast, laser diodes can increase in efficiency with much higher currents than LEDs could handle. Meanwhile, laser-phosphor is able to transmit LiFi data 10 times faster than LED-based LiFi can.

One of the pioneering manufacturers of laser-phosphor lighting is California-based SLD Laser, which has offices all over the world. The company has won the LightFair Technical Innovation Award in both 2019 and 2018, along with multiple IES Progress Report listings, Sapphire Awards, and Prism Awards. Among its new products is a 12,000-lumen SkyBeam spotlight for outdoor applications (its laser-phosphor sources are already being used in autonomous vehicle headlights).

Some of the current challenges with laser-phosphor lighting are higher initial costs, lower CRI phosphors to withstand the intensity of lasers, and some additional safety considerations with laser diodes.

Electroluminescence

Like the other SSLs detailed above, electroluminescence (or EL) produces light when electrons and holes recombine at the junction of semiconductor layers. Similar to OLEDs, EL can produce broad area panels, neon-looking tapes, and thin, linear “wires” of diffuse light (colored or white) with very little power. EL is often used in instrumentation panels and night lights.

Portland, Ore.-based manufacturer Ellumiglow sells EL in tape, panel, and “wire” formats for residential as well as consumer electronics applications. It also sells laser-fiber optic sources that they call “Laser Wires,” which emit colored or white light out of the sides of the fiber over its entire length. Although EL requires very little power and creates negligible heat, it also produces lower levels of light at a relatively higher cost. As a result, EL is likely to remain in specialty, accent, and instrumentation niches for the foreseeable future.

Stay Informed

Now that showrooms and consumers are familiar with LED lighting, there will be less of a learning curve for showroom staff and consumers to adopt OLED, laser-phosphor, and even electroluminescent sources. Consider looking at these “other SSL” sources as ways to differentiate and stay at the forefront of SSL technology.

David Shiller is a Technical Contributor to enLIGHTenment Magazine and President of Lighting Solution Development, a leading consulting firm to lighting manufacturers. David has two decades of technical marketing and business development experience in the advanced lighting industry. david@bravobusinessmedia.com