Machine Design

Same power, more light

Scientists at Rensselaer Polytechnic Institute's Lighting Research Center (LRC), Troy, N.Y., have found a way to get significantly more light from white LEDs, without more electrical power.

Prototype LEDs made with a scattered-photon-extraction (SPE) technique put out 30 to 60% more lumens-per-Watt (lm/W) than commercial white LEDs, and 5 more than incandescent bulbs. And even higher efficiencies are possible, says the group.

Commercially available white LEDs combine a light-emitting semiconductor with phosphor to make white light. However, more than half of the photons produced by the phosphor divert back toward the LED where they are absorbed, lowering output. The SPE approach, in contrast, moves the phosphor away from the semiconductor and reshapes the LED lens. The changes let the extra photons escape as visible light instead of being absorbed.

Makers of white LEDs aim to squeeze 150 lm/W from the devices by 2012. The current SPE LEDs are capable of 80 lm/W, compared with modern, compact fluorescent lamps (60 lm/W), and incandescent lamps (14 lm/W).

SPE research is a collaboration between Rensselaer and the Univ. of California, Santa Barbara. Funding comes from the DOE Building Technologies Program and the National Energy Technology Laboratory through its competitive research and development program. The DOE predicts solidstate lighting by the year 2025 could displace incandescent and fluorescent lamps, lowering national energy consumption for lighting by 29%. The SPE technology is patent pending.

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