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

U.K.-based Compound Security Systems Ltd. sells a device to repel loitering teens with a frequency adults can't hear.

WSJ: A California City Is Into Tweeting��Chirping, Actually��in a Big Way