Lighting designers have long sought to conceal luminaires, illuminating spaces so that an inhabitant notices only the light, not its source. Today, the notion that a luminaire could nearly disappear is closer than ever, thanks to evolutions in material technologies. The trend in LED lighting is toward smaller, thinner, more integrated systems that provide optimized performance but are practically invisible.
For our sister magazine, Architectural Lighting, Timothy A. Schuler recently explored the issue of new materials being used in solid state lighting and their impacts on architecture and lighting. Here are some of the highlights:
One of the biggest innovations in the past two years has been remote phosphor technology, which separates the phosphor from the diode. Phosphor is nothing new. The light-emitting substance is the basis of glow-in-the-dark toys, and it’s been integral to solid-state lighting, typically in the form of a coating that is applied to blue LEDs to turn their light white. The key distinction with remote phosphor technology is that the phosphor material is integrated with the diffuser optic, increasing design freedom while decreasing manufacturing costs.
Remote phosphor has been adopted for applications ranging from undercabinet to high-bay spaces, but cost continues to be a barrier for certain types of luminaires. And manufacturers like Intematix continue to search for even greater efficiencies. Currently, the holy grail in the search for new phosphor materials is narrow-band red phosphor, which would allow manufacturers better access to certain portions of the light spectrum. “This is subject to maintaining CRI, but you can get much more efficiency if you have narrow-band red phosphor, because you’re not wasting light in the long portion of the red spectrum,” says Julian Carey, a senior director of phosphor marketing at Intematix. “That’s one of the industry’s priorities.”
One of the things that LED manufacturers do agree on is the superior thermal and optical performance of glass. At the same time, the demand for ever-thinner materials and for ever-smaller sources has made glass less desirable. As a material, glass is highly inflexible. (We won’t even bring up how expensive it can be.) The alternatives, thus far, have been polycarbonate and PMMA (polymethyl methacrylate). Polycarbonate is a type of thermoplastic polymer that enjoys a certain ubiquity in the modern world (the plastic case for Apple’s iPhone 5c, for instance) and is equally versatile in the solid-state lighting industry.
Enter moldable silicone. In the hierarchy of materials, silicone is second only to glass, says Hugo da Silva, the global industry director for LED lighting at Dow Corning, who is an expert in lighting and electronics and an evangelist for his company’s line of moldable silicone products. “Silicone combines the proven properties of plastics and the good properties of glass,” he says. From a performance perspective, moldable silicone withstands high temperatures, high levels of ultraviolet light exposure, and high lumen densities.
First-generation LEDs all used some combination of gallium nitride (GaN) and a substrate made of a different material. Those substrates were made from glass, silicon, silicon carbide, and sapphire. In recent years, however, several companies, including Soraa and Panasonic, have experimented with making the substrate out of GaN as well. Using the same material for both layers creates a much more reliable diode, even when running at incredibly high power densities.
This advantage was not unknown to most LED manufacturers, but the cost of GaN has been prohibitive. GaN-on-GaN has also made possible full-spectrum LEDs that include violet emission. Until now, that’s only been a pipe dream. “Violet-emitting LEDs do not tolerate the lower quality of GaN-on-foreign-substrate,” says Mike Krames, chief technology officer for Soraa. Blue LEDs create light that appears white but, unlike [the] incandescence of sunlight, is not full-spectrum because it lacks violet emission. By adding violet and harnessing the full spectrum, LEDs will be one step closer to imitating natural light.
The Rate of Adoption
LEDs have evolved so quickly that material innovation has struggled to keep up. But in many ways, today’s technologies already have the power to transform the lighting industry. And now it is the industry itself, Dow Corning’s da Silva says, that is lagging behind. LED lamps, for the most part, continue to be designed to mimic existing lamp form factors, and da Silva sees the romanticism of outdated technologies as a fatal flaw, noting that his company has run up against this misplaced nostalgia as it has marketed its moldable silicones. “It’s been a journey the last four years to [create] new technologies that bring a lot of flexibility under the same technology umbrella,” he says. “The challenge is how conservative the industry is.”
This shift would be momentous—and symbolic. Early on, LEDs overpromised and underdelivered when it came to lighting performance. Manufacturers entering the lighting industry from the electronics world had little understanding of the unique and nuanced requirements of architectural lighting. But that is changing. “What people claim compared to the actual performance has significantly improved,” Anderson says. “There’s a better match there. The industry is maturing.”
This is but a sampling of the full story. Read that here, at Architectural Lighting's website.