While phosphor-converted white LEDs are touted for general-illumination and backlighting applications, colored LEDs can serve in many more applications in architectural, entertainment, horticultural, and other segments. Philips Lumileds has added to its color portfolio with a new deep-red emitter. Lebelight Technology has a green emitter that it says can produce 150 to 160 lm.
Philips has a Luxeon Rebel color portfolio that ranges from royal blue (440-460 nm) to deep red (650-670 nm). The deep-red LED is the recent addition and targets applications such as horticulture and entertainment. Moreover, Philips says that some governments require the deep-red color in railway- and roadway-signaling applications.
Deep-red for safety and horticulture
The deep-red LED differs from the standard-red (620-645 nm) offering. The deep-red color is more visible in safety-centric application and Philips rates it at double the drive current of most of the Luxeon color portfolio. The emitter generates 720 mW of radiometric power or radiant flux at 700 mA.
"For more than a decade, Luxeon LEDs have been the first choice for enlivening city centers and architectural wonders, bringing drama to concerts and performances, and ensuring people can move safely on our public transit systems," said Steve Barlow, senior vice president of sales and marketing at Philips. "We are committed to the continuous improvement of our color portfolio and have delivered substantial light output increases."
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Horticulture could prove to be a major consumer of the deep-red LEDs. It turn out that the 660-nm wavelength corresponds to peak chlorophyll absorption in plants as we covered in an article on LED-based horticultural lighting. Plant factories and green houses are moving away from broad-spectrum lights to ones that provide specific wavelengths hoping to induce better plant grow with less energy. Osram has been keen to support such applications introducing deep-red LEDs last year.
The other color in the Luxeon portfolio that has a specialty applicability is the royal-blue LED. It too is characterized at 700 mA delivering 1120 mW, and targets remote-phosphor-based general-lighting applications. Philips introduced the royal-blue LED earlier this year, and we just ran a news story on the remote-phosphor topic with Cree introducing a royal-blue LED.
Brighter green LEDs
Green LEDs, meanwhile have been challenged in terms of lumen output due to a physics phenomenon called the charge separation effect. Research organizations such as Rensselaer Polytechnic Institute (RPI) have been working diligently on brighter green LEDs.
Lebelight Technology of Xiaoyi, China claims to have produced a green LED that delivers 150 to 160 lm at 350 mA of drive current. If the company can cost-effectively produce such a product it could enable advances in general lighting, backlighting, and specialty applications such as horticulture.
Large-screen TV backlights for example can benefit from direct backlighting using clusters of red, green, and blue (RGB) LEDs that improve the color gamut of the picture. But TV makers have gone away from the RGB scheme, in part because they need to combine two green LEDS with each red and blue LED to achieve consistent brightness. Likewise, RGB-based general-lighting fixtures can produce tunable color, but the available green LEDs don't deliver the needed efficiency.