• solid-state lighting;
  • smart lighting;
  • ultra-efficient lighting;
  • light-emitting diodes;
  • laser diodes

Solid-state lighting has made tremendous progress this past decade, with the potential to make much more progress over the coming decade. In this article, the current status of solid-state lighting relative to its ultimate potential to be “smart” and ultra-efficient is reviewed. Smart, ultra-efficient solid-state lighting would enable both very high “effective” efficiencies and potentially large increases in human performance. To achieve ultra-efficiency, phosphors must give way to multi-color semiconductor electroluminescence: some of the technological challenges associated with such electroluminescence at the semiconductor level are reviewed. To achieve smartness, additional characteristics such as control of light flux and spectra in time and space will be important: some of the technological challenges associated with achieving these characteristics at the lamp level are also reviewed. It is important to emphasise that smart and ultra-efficient are not either/or, and few compromises need to be made between them. The ultimate route to ultra-efficiency brings with it the potential for smartness, the ultimate route to smartness brings with it the potential for ultra-efficiency, and the long-term ultimate route to both might well be color-mixed RYGB lasers.