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
Low-energy house as 'standard voltage' compact fluorescent lamps and solid-state lighting with Light-emitting diode-LED lamps, organic light-emitting diodes, and PLED - polymer light-emitting diodes; and 'low voltage' electrical filament--Incandescent light bulbs, and compact Metal halide, Xenon and Halogen lamps, can be used. Solar powered exterior circulation, security, and landscape lighting - with photovoltaic cells on each fixture or connecting to a central Solar panel system, are available for gardens and outdoor needs. Low voltage systems can be used for more controlled or independent illumination, while still using less electricity than conventional fixtures and lamps. Timers, motion detection and natural light operation sensors