Some designers love those sleek lines of recessed light, and some think they’re too bright and already passé. But recessed linear luminaires are everywhere: running up and down walls, skimming architectural transitions, marching or swirling along ceilings, and punctuating spaces in pixelated patterns. Slots can provide strong design character to a space, or they can provide subtle, general illumination where troffers take up too much real estate and downlights are too little. There’s also a sweet spot where slot lighting – done right – follows the lines of the architecture while providing good illumination with balanced brightnesses.

Slot lighting first came in vogue with the advent of T5 and T5HO sources. Long, seamless runs of narrow-aperture downlighting provided workhorse ambient illumination in upscale corporate offices and retail: far more refined than two-by-four troffers. T5 fluorescent is slightly more efficient than T8 and fits comfortably in a 3 inch aperture. But in narrow apertures it’s difficult to get the light out of the fixture, and delivered lumens fall precipitously.

Hilton Columbus
This lighting design for a floating ceiling by Ardra Paige Zinkon of Tec Studio Inc. echoes the linearity of the interior finishes. Zinkon won a SOURCE Award in 2013 with these recessed slots housing T5HO fluorescents.

Enter LED. Fluorescent tubes emit 360° around the axis of the lamp, but LED is an inherently directional source. “I would venture to say we have the capability of illuminating office environments, for instance, at easily 75 percent less energy consumption than we did in the past, providing the same amount of light within the space,” said George C. Bosson, principal consultant at be*light and founder of a.light Architectural Lighting, a linear lighting manufacturer.

Plus, they’re smaller.

“I’ve seen slot luminaires as small as ¾ of an inch, and you can go even smaller if you want. But I don’t know how much light you’re going to get out of it,” said Bosson, emphasizing that even with LEDs there is a difference between source lumens and lumens delivered out of the fixture.

Slots run anywhere you can regress the housings into drywall or attach them to T-bar. Complex geometries can be designed and pre-fabricated in the factory or long runs can be cut in the field to step, slant, zigzag or even curve. LED arrays may be side-mounted for smooth indirect lighting, still with a very narrow aperture; but most fixtures are lensed to diffuse the LED point sources within. Reflectors can provide less-blobby distributions and excellent wallwashing. New and upcoming generations of slots will accommodate RGB color mixing along with track lighting, sensors, cameras, speakers and an unlimited array of electronics.

Undoubtedly, LED has launched the proliferation of slot lighting in contemporary architecture, but it brings with it some challenges.

Just because you can…

Janet Nolan, principal at J S Nolan + Associates Lighting Design, appreciates the fixture’s small aperture and clean, seamless joins. “It’s a lensed luminaire, so it’s going to have high surface brightness. And with LED it’s even more apparent, because LED is a much brighter source,” she said, emphasizing the need for well engineered optics. “We still do not like to use it in low ceilings for office applications.”

J S Nolan + Associates hits that sweet spot at the grand-scale San Jose Convention Center: changeable lines of light that enhance the architectural character, provide meaningful illumination and balance brightnesses.

Nolan advises careful design that manages brightnesses to avoid glare and over-lighting. “Most product is available in at least two, maybe three outputs. Even with those, which give a fair amount of flexibility, we would probably still be dimming it,” she said. “It does give you the ability to tune the light where you need it to be.”

To offer different lumen packages, measured in lumens per foot, manufactures may choose to decrease the density of LEDs on the array or to underdrive the LEDs. Where higher illumination levels are required, a designer may go to a larger, 6 inch aperture to spread out the brighntess of the lens. This may also make sense in larger spaces with high ceilings, even more so outdoors.

“We do love it, but we hate it when it’s not properly done, because it can be a real source of glare,” she said. “Architects and designers in general have embraced the linear slot light look. In some cases, I think a little too much because the brightnesses do have to be managed.… It has to be purposefully orchestrated.”

As a philosophical point, Alfred Scholze, principal of Alfred Scholze Associates avoids “statement” lighting: “Usually my work is more directed toward specifically lighting areas, rather than having the fixtures read in the ceiling as a design element. Usually having to spend your energy on a visual element is kind of tricky. I’d rather get the light down where you need it,” he explained.

JESCO Tumi Store in Beverly Hills
Slot lighting integrates seamlessly here in a high-ambient retail application: a Beverly Hills store designed by Tumi’s in-house design team.

Scholze recommends a high-quality open fixture to keep the ceiling as quiet as possible. Instead of round- or square-aperture downlights, he’s using 6-inch wide slot lighting in various lengths. “The ceiling disappears, basically. It’s really great.”

Teleconferencing rooms are particularly tricky, he said. “What you want to stay away from is reflected glare in screens, which is always a problem. But with these smaller apertures you can control the light a lot more successfully than you can with [two-by-fours].”

Bosson prefers the middle road: “The way to do it right, I learned from Bill Lam, is to understand what the architectural intent is, and to compliment it and enhance it if possible,” he said. He objects to “glarish” brightly lensed slot lighting laid out like two-by-fours. “It’s just boring. That just happens to be my taste,” he said. “When it’s used as intended it provides ample illumination but it does draws the eye’s attention to the architectural details.”

Lois I. Hutchinson

About Lois I. Hutchinson

Lois I. Hutchinson is a freelance writer specializing in lighting and energy issues. She is also the content marketing mastermind behind Inverse Square LLC, a Los Angeles–based consultancy. Contact her via with your comments and any article ideas that concern the lighting community here in the Southwest.

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