Since the development of the first commercial visible light-emitting diodes (LEDs) in 1968, LED technology has undergone a series of both evolutionary and revolutionary changes. For the first 25 years of their history, the materials available for LED fabrication (primarily gallium phosphide (GaP) and gallium arsenide phosphide (GaAsP)) were low in efficiency and allowed LEDs to be used primarily as lowbrightness indicator lamps and alphanumeric displays. Moreover, their spectral range was limited to yellow-green, orange, and red.
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