Intematix has introduced the ChromaLit Linear remote phosphor that enables a linear white light with uniform luminance over its length, and which has the aesthetic advantage of appearing a very pale yellow in its off-state.
Intematix calls it a white off-state remote phosphor – like I say, I’d call it a pale yellow — which is much less intrusive than the L-Prize bulb’s color. Intematix says ChromaLit is capable of 130 lm/W, and can produce up to 2500 lm/ft. (Fluorescent lighting emits about 100 lm/W.) My 12-in. unit is spec’d at 1100 lm, 3500K, 80 CRI. I used it all day in my office and loved it. Its off-the-shelf exterior power supply used 11W, or about the same as an 800 lm 60W-replacement bulb, while putting out about 1/3 more lumens.
The white coating on the phosphor is not just for appearances sake: It optimizes the phosphor to get more white light converted from the blue to enhance efficacy.
A cut-away shows the simple design:
Its temperature stabilized at about 120F; I could easily hold it in my hand.
Volume pricing for the technology looks very attractive, with a rough number at the system level of about $6/ft. And, maintenance costs for fluorescent lights, both their ballasts and their tubes, are significant compared to an LED lighting system of at least 25,000 hrs.
Best bet for non-directional light?
I love non-directional light, and linear lighting is the closest we’ll come to it in the near future. If it were up to me, all interior spaces would be illuminated by a glowing ceiling, mimicking natural sunlight as closely as possible. I’ve gone so far as to install overhead fluorescent lights in several rooms of my house to get that bathed-in-light feel. However, fluorescent tube lights have some severe drawbacks. Their light is often cold and blue-ish with a poor color quality, or CRI. And I particularly hate the noise the ballast makes as it turns on and then keeps running. I fee like I’m on a factory floor. This is a market that’s ripe for innovation and LEDs.
And it’s a huge market: While few residential customers have gone as far as me in installing them in their home, they are the dominant light source for commercial and factory environments. The earliest technology solution for LEDs was a long, thin array of LEDs with the same form factor of a fluorescent tube. The problem with this approach is two-fold: Pixilation, or the distracting effect of hundreds of tiny points of light in the ceiling, and how to adequately heat sink the LEDs since high temperatures affect their lifetime and performance.
The second approach to replacing fluorescent lighting, introduced by Cree, makes use of a troffer, a metallic enclosure that surrounds the LEDs and bounces their light off of the troffers overhead surface, thus hiding the LEDs and using the troffer backing as the source of light. This approach works well (Cree troffer review) but it requires a large area of the ceiling and considerable metal in the enclosure.
Remote phosphors promote color stability
The third approach is to use a remote phosphor, chemical compound that converts the light from the blue LEDs into white light – is kept separated at a distance from the LEDs. The advantage of using a remote phosphor is that it separates the phosphor from the heat of the LED, which keeps the phosphor stable and gives a long life to the light. The L-Prize bulb has passed 25,000 hrs of life testing by the DOE with no degradation of its color. In addition, the Smithsonian LED retrofit Gateway project seems to indicate that heat is the number one cause of color-shift in direct phosphor lamps.
The disadvantage was that people aren’t used to the appearance of yellow-when-off lights; This was one of the barriers to market acceptance that the Philips’ L-Prize bulb faced. (The other barrier being its high price.) So the less-intrusive pale yellow color of the ChromaLit can make a significant impact in consumer acceptance.
While the white-when-off remote phosphor of the ChromaLit Linear is new, ChromaLit phosphors have already found use in under- cabinet lights, such as the Kickstarter-backed Klauf Light.
What about other approaches for using remote phosphors in linear lights? Philips’ tube-lighting replacement LED (TLED) is one, and the company has announced it will begin manufacturing in 2015. The TLAD, capable of as many as 200 lm/W uses a combination of red and blue LEDs in a light mixing chamber in addition to the remote phosphor. While the phosphor and the blue LEDs can produce a white light with lots of yellow and blue wavelengths, it relies on the red LEDs to add the warmer wavelengths and get a high CRI.
However, mixing LED colors is a tricky and involved process because the different LEDs have different temperature vs intensity curves. Yes, a sophisticated company like Philips will be able to tweak the LEDs and control their warm-up and aging algorithms, but it will be complex and more expensive than a straight-forward remote phosphor approach optimized for a blue LED’s wavelength. Chromolit’s approach looks like a winner for an economical design with good light output and acceptable color quality and that looks good, even when off.