The Future of LEDs: Not What Most People Think


If you get most people talking about LEDs, you hear about what a 60-W, 75-W, or recently, even 100-W screw-in replacement costs at Home Depot.  (Yes, I wrote “100-W”; they’re coming.)  Or else it’s about dimming with legacy triac dimmers. I’m just back from Lightfair 2012 in Las Vegas, and that’s not what the show was about.  What it’s about is new buildings – ranging from warehouses to stores, to restaurants retail centers, and public lighting – streetlights, parking garages, shopping malls, that sort of space.  If LEDs are to be in the home, they’ll be in major remodels and new construction, subtly lighting the bathroom, the kitchen, and the home theatre – places like that.  To be sure, the worldwide outlawing of incandescents will create a huge market for screw-ins, but a very price-sensitive, low-margin market, with brutal competition, some shoddy products from the usual suspects, and an ever skinnier long tail of sockets to fill as new kinds of movable lamps that never need light-source replacements multiply.  Think of vacuum tubes.  For that matter, think of gas mantles.

As I’ve written before, the most attractive feature of LEDs for lighting large spaces is that they can be turned on and off easily.  That’s also true of halides, but not of any of the light sources that require striking an arc through a plasma.  Halogen lamps also burn out. The big deal about turning these things on and off is that they’re not using any electricity when they’re off.  Sure LED’s are efficient when they’re on, but they’re infinitely efficient – energy-wise when they’re off.   (Except that doesn’t quite work out, if you need occupancy sensors to turn them on when they are needed.  Or does it? Occupancy sensors or movement sensors, can operate on a low duty cycle and still be effective. This illustrates the opportunity that LEDs create for electronic designers – it isn’t the light source that’s important, it’s the electronics that control them.)

The other efficiency factor that the guys in the Lightfair booths always promoted was that the longevity of the light sources means that whosever responsible for maintenance in the places using the high light-output fixtures is paying far less in personnel costs for routine maintenance, especially of those personnel would have been Class-1 electricians.

One interesting trend is toward the use of fewer, brighter LEDs in this kind of industrial lighting.  (And it’s been around, especially in streetlights) for there to be a trend. A few years ago, this kind of lighting would use multiple series-strings of ten LEDs to achieve the desired lumen output.  (Ten LEDs with a nominal 4-V forward drop for each would take a 40-V dc driver with modest current requirements. But even though the brighter LEDs and higher-current drivers cost more, the trend is definitely toward fewer, brighter, LEDs, partly because of higher overall efficiency, partly (I think) because of higher reliability.

I even saw multiple, larger, high-brightness LEDs in a demo of residential down-lights at Creative Systems Lighting’s (CSL) booth.  In that case, it was a matter of balancing color rendering index (CRI) with multiple LEDs, but that brings up another aspect of what people were talking about at Lightfair. One of CSL’s boasts is that the light elements in its fixtures snap in and out and that they can ship replacements virtually instantaneously.  The key feature of that though, is that the replacements will be color-bin- and date-bin identical to the originals.  Whatever the customer saw before, it will be exactly the same with the replacement.

Speaking of exhibitors, Cree is a must-see at any lighting show.  The most interesting message there, from a design engineering point of view is what Cree PMM Paul Scheidt told me about TEMPO 24, a new suite of Cree of test services for LED luminaires. (Luminaires art the customer-built end products that Cree’s light-emitting diodes go into.) ”TEMPO” refers to the range of tests: (thermal, electrical, mechanical, photometric, and Optical. These are combined IES LM-79-08 photometric testing.

LM-79 testing is the standard method for taking electrical and photometric measurements. To that, TEMPO 24 can add binning and color point evaluation, chemical compatibility and TM-21 lifetime projection. Cree currently provides TEMPO Services out of its Durham, N.C. and Santa Barbara, Calif. Cree Technology Centers.

Few non-LED semiconductor companies attend Lightfair.  NXP showed GreenChip-technology-based drivers for dimmable and non-dimmable LEDs and for higher-power LED drivers for high bay and low bay lights in commercial/industrial and street-lighting applications. NXP also showed how its ZigBee JenNet-IP network-layer software for the “Internet of Things,” makes it possible to extend connectivity, two-way communication to control to home networks of  up to 500 devices.

Maxim Integrated Products announced a new G-3 PLC-based reference design for the control and power measurement of outdoor luminaires.

Texas Instruments introduced the LM3447 ac-dc LED driver with constant power regulation. It includes dimmer detect, phase decoder, and adjustable hold-current circuits for off-line, isolated LED lighting applications.

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Don Tuite

Don Tuite covers Analog and Power issues for Electronic Design’s magazine and website. He has a BSEE and an M.S in Technical Communication, and has worked for companies in aerospace,...
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