The emergence of efficient solid state light emitters was the result of the remarkable breakthroughs in the late 1980s and early 1990s in GaN-based materials and light emitting diodes. Over the past two decades, the continued progress in blue LED efficiency resulted in a revolution in lighting. While the basic physics of nitrides LEDs operation are well understood, nitride LEDs have still open questions, and their reaching physical limits at all wavelengths still raises major challenges.
Lighting has had a great historic importance and did put a continuing demand on energy resources, despite the huge progress in efficiencies throughout centuries (Fig. 1a). Basically, every new energy source was first put to use to realize better, more efficient lighting (Fig. 1b). As shown in Fig. 1a, lighting sources made enormous progress since the early 19th century, and then improved fifty-fold from 1900–1950 with improvements in incandescent bulbs and then five to ten-fold with the introduction of fluorescent lighting in 1950. Today ~15% of electricity is used for lighting.
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