What is solid-state lighting?

Solid-state lighting is a new technology that has the potential to far exceed the energy efficiencies of incandescent and fluorescent lighting. Solid-state lighting uses light-emitting diodes or "LEDs" for illumination, the same kind of practical and inexpensive devices that provide the letters on your clock radio. The term "solid-state" refers to the fact that the light in an LED is emitted from a solid object—a block of semiconductor—rather than from a vacuum tube, as in the case of incandescents and fluorescents. There are two types of solid-state light emitters: inorganic light-emitting diodes (LEDs) or organic light-emitting diodes (OLEDs) for white-light illumination. 

What is a semiconductor?

A semiconductor is a substance whose electrical conductivity can be altered through variations in temperature, applied fields, concentration of impurities, etc. The most common semiconductor is Silicon, which is used predominantly for electronic applications (where electrical currents and voltages are the main inputs and outputs). For optoelectronic applications (where light is one of the inputs or outputs) other semiconductors must be used, including GaAs, InP and GaN. For inorganic LEDs the most common semiconductors are: InGaN, which emits near-UV, blue and green light; and InGaP, which emits amber and red light.

What is a semiconductor LED (Light Emitting Diode)?

A light emitting diode (LED) is a small semiconductor device that emits light in one or more wavelengths (colors). A diode is a device with two electrodes through which a current can be passed in only one direction. The diode is attached to an electrical circuit and encased in a plastic, epoxy, resin or ceramic housing. The housing usually consists of some sort of covering over the device as well as some means of attaching the LED to an electrical source. The housing may incorporate one or many LEDs. A LED is typically 1 mm2 in size, or approximately the size of a grain of sand. However, when encased in the housing, the finished product maybe several mm or more across.