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Optoelectronics/Displays??

Pushing white light efficiency through GaN-on-GaN

Posted: 23 Dec 2013 ?? ?Print Version ?Bookmark and Share

Keywords:Philips Lumileds? GaN-on-GaN? white LED? Soraa? luminous efficacy?

Then back on the white light quality issue, David only had praise for the new devices, with a measured CRI of 95. Because Soraa's chips emit violet light to pump a proprietary mix of phosphors, the company is able to generate cyan light, as opposed to the cyan gap of common blue-pumped LEDs.

"But the CRI is only part of the story when it comes to quality of light," emphasized David. "It is only a metric for so-called color fidelity, and a debatable one according to ongoing academic research."

For better whiteness rendering, a lot of everyday objects (including white shirts, paper, plastic and even your teeth) contain optical brightening agents that absorb UV and violet light and emit blue, making white look brighter. By emitting violet light, Soraa's LEDs are able to properly activate the whitening agents and render white objects, which regular white LEDs can't do.

light spectrums for different white lights

Figure 3: Comparing light spectrums for different white lights

David would not be too specific about the GaN substrates the company uses, except that they are commercially available Hydride Vapor Phase Epitaxy (HVPE) GaN substrates. But he acknowledged that the company is also doing research on the growth of bulk GaN, experimenting with bulk GaN wafers (so fare too small and expensive to be commercially viable).

As for the future of GaN-on-GaN LEDs, David is very optimistic. "Currently, the LED market is still vertical, manufacturers want to do it all by themselves. But substrate price erosion alone will drive further adoption of this technology."

"Then if in a few years we can make cheap GaN substrates, the benefits will be so compelling for the whole LED industry, that you will ask, why bother do anything else?"

Helping GaN-on-GaN LEDs take the lighting world by storm as David would bet, Soraa is commercializing a slick MR16 lamp that received the 2013 Red Dot Award for all its innovative features.

Later after his keynote, David was kind enough to demonstrate the lamp against the nearest competing device, and the color rendering difference was striking. Exit the yellowish tones! Welcome the bright whites.

David is cautious to express the luminous output of Soraa's products as the center beam candlepower (CBCP), arguing that communicating in lumens can be deceiving, because the lumens need to be in the centre beam (not outside a specific beam angle) to be considered as useful.

The company said it achieves a high CBCP by combining a high lumens output from a small source size together with good optical design. Here again, CBCP comparisons should only be made among lamps designed with the same beam angle. With this in mind, David gave us some elements of comparison.

"For instance, you will find that for a 3000K 24 degree lamp, Philips' MR16 lamp outputs just about 2000cd of CBCP at 10W (40W equivalent, CRI80) while a Soraa product with a CRI of 95 can deliver a CBCP of 2750 cd (11.5W, 65W equivalent)," David noted in complementary email exchange.

- Julien Happich
??EE Times Europe


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