Light-emitting diodes (LEDs) are highly efficient, but they can't directly produce white light. Though a blue LED can be coated with a phosphor that alters some wavelengths to yield a whitish mix, the resulting light has a bluish cast, and some energy is wasted as heat in the process. A new LED lamp avoids this problem by using an optic coated with quantum dots--bits of semiconductor material a few nanometers in diameter. When excited by a light source, the dots radiate light in wavelengths that vary according to their sizes. The optic--coated with dots in specific sizes and ratios--appears orange when the light is off (left) but radiates white light when the underlying blue LED is on (right). The result: LED lamps that are 50 percent more efficient and produce better-quality white light.

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