The first widely available replacements for incandescent light bulbs, compact fluorescent lamps (CFL), are now (as of 2010) joined by two alternative technologies - light-emitting diode lamps (LED) and electron stimulated luminescence (ESL) lamps. Both LED and ESL technologies are mercury-free, eliminating the need for special disposal or handling, and both have long lives when compared to incandescent bulbs.
LED lamps are used for both general and special-purpose lighting. Where colored light is needed, LEDs come in multiple colors, which are emitted with no need for filters, and also produce a more robust color than incandescent bulbs. This improves the energy efficiency over a white light source that generates all colors of light then discards some of the visible energy in through a filter.
Compared to fluorescent bulbs, advantages for LED light bulbs are that they contain no mercury, that they turn on instantly, and that lifetime is unaffected by cycling on and off, so that they are well suited for light fixtures where bulbs are often turned on and off. LED light bulbs are also less apt to break.