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Lighting trends: Solid State Limelight

Aug. 1, 2012
SSL designers could soon take a broader perspective that includes styling and ergonomics.

Lose the geek speak.

That could be the subtitle to recent remarks by head of Cree Inc. marketing and applications Michael Watson. “Every lumen-per-watt increase in SSL from now on makes new applications possible. But there is not a lot of perceived value delivered to customers today by marketing efforts of the SSL industry,” he says. “Customers never ask about complicated specs for LED lighting. They just want an LED that fits their chandelier, or they want to know why they should switch.”

Watson thinks the SSL industry would be well served by changing the way it explains the benefits of its latest high-brightness innovations. “We have to couch benefits in terms of existing applications. Lighting customers know what they have now. SSL makers must explain their products so customers understand where they fit with what they know,” he says.

Despite difficulties explaining benefits, Watson thinks SSL will see a faster adoption rate in the near future. “SSL lighting is already at cost parity with traditional lighting if you don’t only look at bulbs and tubes. The conventional view is that we are in the adaption phase of the technology, but this is based on the assumption we are competing for the existing lighting market and that we are using the same business model as conventional lighting,” he says. “I think we will see a fast adoption path from here, but the business models must change. We need new business models that don’t focus only on replacement and on price as the sole differentiator.”

Other lighting suppliers might add another item to Watson’s list of key business developments: standards. “SSL is being slowed because there aren’t accepted standards yet for key lighting components,” says George Kelly, Avnet Inc. technical specialist and LightLab manager. “We don’t, for example, see much of the Zhaga standard at this point. I think people would love to get a standard module (for light engines) but I don’t think we are there yet. There are still a lot of companies populating boards with LEDs.”

And there is still a lot of custom work when it comes to LED installations. “We see retail and restaurant chains and factories who want LED lighting that will find a company able to design and build something specifically for them. If you are big enough, you can do this,” says Kelly.

One trend that is letting LEDs become more mainstream sources of illumination is the use of modularity. LED suppliers are far more likely to bundle multiple LEDs into light engines that can more easily be built into fixtures, rather than provide single LED die.

Though Cree’s Watson may not think SSL’s future lies in the replacement market, Avnet is seeing appreciable activity there. “Fluorescent tube and Par 38 down light replacements are moving, at least among our customers who tend to be smaller companies doing something custom,” says Kelly. Interestingly, that is not the case for dimmable LEDs. “Fluorescent tube replacements don’t need it, and I am not sure how many people have dimmers in more than an outlet or two of their homes,” says Kelly. “It might be more important if you are competing with HID lamps in high-bay lighting. You can sometimes convince people to go with LEDs in these applications by showing you can dim the light and turn it on-and-off quickly.”

He says a classic example of where LED dimmability is a selling point is in parking lots with motion detectors: “Dim it to 50% after midnight. If someone drives in, bump it up to full intensity. In that scenario, LEDs can have a tremendous savings over HID lamps which take awhile to warm up and are hard to dim.”

To keep the costs down for applications such as parking lot lighting, Avnet says a lot of its customers are going with multiple low-power LEDs in a chip-on-board type packaging scheme rather than fewer but more expensive LEDs. “It is simple to make a high-powered light source this way,” says Kelly. “Just solder wires to the board. Lots of off-the-shelf ballasts will work in these schemes. Putting 30, 40 or more LEDs on a board is cost effective because their price has been driven down due to their high-volume use in TV backlights.”

Another electronic components distributor seeing a more modular approach in SSL is Mouser Electronics. “There are a variety of component guys who have been moving toward a higher level of integration,” says Mouser Technology Specialist Paul Golata. “They add drives and packages to their components to come up with a module, and that module may or may not adhere to a standard like Zhaga.”

Golata also sees a lot of SSL designs trending toward use of multiple lower-power LEDs. “Almost every major LED supplier now is moving away from one-watt to half and quarter-watt devices to give a more uniform, homogeneous light. This is particularly true of fluorescent tube replacement applications,” he says. “There is a slight improvement in cost and you can dial in a more exact level of lighting in a linear light strip when you use quarter or half-watt LEDs.” Thermal issues also tend to be more easily dealt with when the design uses multiple lower-power devices rather than a few high-power LEDs concentrated in a small spot.

And Golata thinks LED dimmability is likely to become more of a competitive point. “This is the first year I’ve seen LEDs that are both dimmable and that can mimic the color changes you see in a dimmed incandescent light,” he says. “You are also starting to see people fighting about how low their dimmers can go. On the driver side, the degree to which you can control the LED precisely down to the barely-on level is probably going to become a point of differentiation.”

Packaging performance

It looks as though LED costs will continue to drop in the near future thanks in part to research work in chip packaging that is starting to come to fruition. The DOE’s cost reduction roadmap forecasts a halving of LED packaging costs by 2015, and developments that support that goal include plastic-leaded chip carriers (PLCCs). Ilkan Cokgor, Everlight Electronics vice president of global marketing, says PLCCs have the potential to reduce LED costs and thermal issues. For one thing, PLCCs can distribute light and heat by spatially distributing LEDs. Newer versions of PLCCs can house multi junction chips to improve current spreading and thus be brighter. Modifications in the window size and side-wall slope of the package also promote better light emissions, as do recent improvements in the purity of nitride phosphors used in the package window.

Cokgor also says manufacturers can get LED reflector costs down by moving away from injection molding and toward transfer molding, this despite the fact that thermosetting plastic used in transfer molding can be pricier. The difference in package price comes partly because there is little material wasted in the transfer molding process – all the material in the mold goes into the part. In contrast, material in the gating system of an injection mold is lost in every shot.

Another improvement in packaging technology lies in new die attach pastes having a high thermal conductivity. This is important, Cokgor says, because heat affects package lifetime and die attach paste is one of the bottlenecks to reducing the package’s thermal resistance. Increasing thermal conductivity also boosts package reliability. Cokgor says Everlight has seen LED temperatures drop from 54.3 to 47.9°C simply by using a better paste.


Avnet Electronics, Phoenix, Az.,www.avnet.com
Canaccord Genuity, Canada,www.canaccordgenuity.com
Cree Inc., Durham, N.C.,www.cree.com
Mouser Electronics, Mansfield, Tex., www.mouser.com
Everlight Electronics, Taiwan,www.everlight.com

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