Lighting: the progress & promise of LEDs

摘要

Advances in light output power from LED sources continue, with one of the latest markers being the development of a 1200 lumen white LED lamp by Cree. (It would be equivalent to a 75W incandescent bulb.) Although it is still a long way from commercial availability, it is one of the latest milestones towards developing general lighting products from solid state light sources. The laws of physics are not on the side of the conventional lighting sources with the incandescent lamp being only about 5% efficient (much less for colours) and the fluorescent lamp about 27% (70% for the ultraviolet output, but the remainder is lost by a factor of 0.3 to the Stokes (wavelength) shift that provides the white light). The dimming efficiencies of the two main lighting sources are also poor - 50% dimming of a tungsten filament still draws 85% of the power, and fluorescents have little dimming capability. LEDs have many advantages and they are revisited in Table 1.