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
LED tattoo irritation because they are nanometers thick. LED tattoos would not interfere with normal physiological processes. The U.S. Food and Drug Administration (FDA) have approved LED technology but LED tattoos are undergoing continual development. One such medical application would be silk-silicon LEDs to create photonic tattoos which would assist in blood-sugar readings. Perfected for clinical use and mass production, these devices could see patients sent home from the GP or from surgery with a monitoring system that does the job of several heavy-duty machines—like electromyographs, an EEG or electrocardiogram—normally confined to hospitals. LED tattoo A light-emitting diode tattoo is a type