Light-emitting diode into a lower energy level and releases energy in the form of a photon. The wavelength of the light emitted, and thus its color, depends on the band gap energy of the materials forming the "p-n junction". In silicon or germanium diodes, the electrons and holes usually recombine by a "non-radiative transition", which produces no optical emission, because these are indirect band gap materials. The materials used for the LED have a direct band gap with energies corresponding to near-infrared, visible, or near-ultraviolet light. LED development began with infrared and red devices made with gallium arsenide. Advances in materials science
Light-emitting diode In this case, the bond wire(s) are attached to the ITO film that has been deposited in the LEDs. The YAG phosphor in the LED's encapsulation compound is why white LEDs look yellow when off. Some LED light bulbs use a single plastic cover with YAG phosphor (remote phosphor) for several blue LEDs instead of using a diffuser and single chip white LEDs. Remote phosphor LED light bulbs may have behind the plastic cover a white plastic reflector. Others shape the remote phosphor as a dome, or sphere, and place it atop a single PCB containing blue LEDs; this assembly