Phosphors and coloured LEDs. Light-emitting diodes (LEDs) are used in solid-state lamps. In contrast to incandescent light bulbs, LED lamps last for longer and are more efficient. A range of phosphors are used to produce the correct colours. The most common combination is a blue LED with one or more phosphors to create a white LED. Many of the phosphors contain rare-earth elements. The most common LED phosphor is yttrium aluminum garnet (YAG) doped with cerium (Ce), while TAG phosphor contains terbium (Tb). Silicate phosphors such as BOSE and nitride phosphors are commonly doped with Ce or europium (Eu). Photographed in August 2005.