2013-04-15

Monday Roundup: Hybrid LEDs Using Organic Dyes

This week: the right and wrong way to replace streetlights, GaN-on-silicon indicator LEDs, and an LED-lit bathtub.

Hybrid LEDs sound promising
A research team from the University of Palermo in Italy and the Lausanne, Switzerland, semiconductor foundry Novagan has developed a less expensive and less toxic way to fabricate a white-light LED, using the common organic dye Lumogen, which is "available [from BASF] in a large palette of colors from the UV to the IR at the same low cost." The researchers say the Lumogen dyes can give white LEDs reduced environmental impact and high quantum yield -- 91 percent vs. Ce:YAG's typical 75 percent. The dye is applied by dipping or spinning. It has good thermal stability and resistance to weathering.

Emission spectra of a cold-white LED (blue plot) obtained by a solution of Lumogen F Yellow 083 and a warm-white LED (red plot) obtained by a solution of Lumogen F Red 305 and Lumogen F Yellow 083. Both LEDs are pumped by a 450nm blue LED.
(Source: Mosca, Caruso, Zambito, Macaluso, Cali, and Feltin.)

Plessey launches with GaN-on-silicon indicator LEDs
The British company's Plymouth fab has begun turning out its first GaN-on-silicon LED product. A spokesman told Electronics Weekly that the product is available to sample now and will be available in production quantities in six weeks. Made on 150mm silicon wafers, the indicator LEDs deliver 2lm at 20mA from a 3.5x2.7mm PLCC-2 package.

"Inherently we are in the order of 80% less than the sawn-die cost of silicon carbide LEDs," the spokesman said. The package and the die each represent roughly half the cost of the finished device in these small packages.

Replacing streetlights, the right way and the other way
The Canadian city of Kingston is doing this the right way. The US city of Cleveland is doing it that other way.

In Kingston, "the project is city wide and expected to be largely completed by the end of 2013 at a cost of $4 million," the Kingston Herald said. Following a successful trial in 2011, the city is replacing about 10,000 streetlights with LEDs with no apparent muss nor fuss.

Cleveland, on the other hand, made a no-bid deal in 2010 with the Chinese LED maker Sunpu-Opto Semiconductor Ltd. for an exclusive contract. In exchange, the company agreed to put its North American headquarters in Cleveland, creating 350 jobs there. Public outcry scuttled that deal, and an open bidding process began. No compliant bids were received -- from US suppliers or anyone else.

It took the city a year to come up with a new plan, and now four varieties of LED streetlights will be tested in a pilot program. But Cleveland Public Power representatives could not answer Cleveland City Council members' questions about whether the fixtures were made or assembled in the US.

Take my advice: Do it like Kingston.

A bathtub with built-in LEDs
Want a healing personal experience? The Hotaru bathtub incorporates LEDs to surround you with a light show, either of your own devising or randomly changing.

The tub is available in Japan (come to think of it, shipping it out of the country could be prohibitively expensive) and costs around $15,000.

— Keith Dawson , Editor-in-Chief, All LED Lighting