Philips' solution is to combine two blue and one red element, but use a green phosphor filter to convert one of the blue LEDs to green.

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Generally LED bulbs use either a combination red, green and blue LEDs to create white light, or they use a phosphor coating (more common) in combination with a blue LED.

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These can be made to emit white light by coating the device with a phosphor compound that absorbs part of the blue light and re-emits it as yellow.

ECONOMIST: Lighting: A brilliant new approach | The