A light-emitting-diode lamp is a solid-state lamp that uses light-emitting diodes (LEDs) as the source of light. Since the light output of individual light-emitting diodes is small compared to incandescent and compact fluorescent lamps, multiple diodes are used together. LED lamps can be made interchangeable with other types. Most LED lamps must also include internal circuits to operate from standard AC voltage. LED lamps offer long life and high efficiency, but initial costs are higher than those of fluorescent lamps.
General purpose lighting requires white light. LEDs by nature emit light in a very small band of wavelengths, producing strongly colored light. The color is characteristic of the energy bandgap of the semiconductor material used to make the LED. To create white light from LEDs requires either mixing light from red, green, and blue LEDs, or using a phosphor to convert some of the light to other colors.
The first method (RGB-LEDs) uses multiple LED chips each emitting a different wavelength in close proximity to create the broad white light spectrum. The advantage of this method is the fact that one can adjust the intensities of each LED to "tune" the character of the light emitted. The major disadvantage is the high manufacturing cost, which is important in commercial success.