LEDs and Solid State Lighting

from Various Sources, including Wikipedia

LEDs (light emitting diodes) used as a replacement for incandescent light bulbs and compact fluorescent lamps are known as solid-state lighting (SSL) - packaged as a cluster of white LEDs grouped together to form a light source. LEDs are moderately efficient; the average commercial SSL currently outputs 32 lumens per watt (lm/W), and new technologies promise to deliver up to 80 lm/W. The long lifetime of LEDs make SSL very attractive. They are also more mechanically robust than incandescent and compact fluorescent light bulbs and fluorescent tubes. Currently, solid state lighting is becoming more available for household use but it is expensive, although costs are decreasing. LED flashlights and bicycle headlights have become widely available and inexpensive. The Fremont Experience in Las Vegas is a 1500-foot-long (500 meters) LED display, and millions of homes have LED televisions and computer monitors.
 
Incandescent bulbs are much less expensive but also less efficient than LEDs, generating from about 16 lm/W for a domestic tungsten bulb to 22 lm/W for a halogen bulb. Fluorescent tubes are more efficient, providing 50 to 100 lm/W for domestic tubes (average 60 lm/W), but are bulky and fragile and require starter or ballast circuits that sometimes buzz audibly (particularly in cold weather, when they may not even start). Compact fluorescent lamps, which include a quiet integrated ballast, are relatively robust and efficient and fit in standard light bulb sockets. CFLs do still emit a quiet buzz, while LEDs are completely silent.
 
LEDs are now well established in applications such as traffic signals and indicator lamps for trucks and automobiles. High output LED fixtures suitable for general architectural lighting applications are beginning to appear on the market with system efficacies of up to 56 lumens per watt, which is comparable to fluorescent systems. Proponents of LEDs expect that technological advances will reduce costs such that SSL will replace incandescent and fluorescent lighting in most commercial and residential applications.
 
Due to their monochromatic nature, LED lights have great power advantages over white lights when a specific color is required. Unlike traditional white lights, the LED does not need a coating or diffuser that can absorb much of the emitted light. LED lights are inherently colored, and are available in a wide range of colors. A recently introduced color is emerald green (bluish green, about 500 nm) that meets the legal requirements for traffic signals and navigation lights.