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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