Artificial lighting for general illumination purposes accounts for over 8% of global primary energy consumption.
However, the traditional lighting technologies in use today, i.e., incandescent, fluorescent, and high-intensity discharge
lamps, are not very efficient, with less than about 25% of the input power being converted to useful light. Solid-state
lighting is a rapidly evolving, emerging technology whose efficiency of conversion of electricity to visible white light is
likely to approach 50% within the next years. This efficiency is significantly higher than that of traditional lighting
technologies, with the potential to enable a marked reduction in the rate of world energy consumption. There is no
fundamental physical reason why efficiencies well beyond 50% could not be achieved, which could enable even greater
world energy savings. The maximum achievable luminous efficacy for a solid-state lighting source depends on many
different physical parameters, for example the color rendering quality that is required, the architecture employed to
produce the component light colors that are mixed to produce white, and the efficiency of light sources producing each
color component. In this article, we discuss in some detail several approaches to solid-state lighting and the maximum
luminous efficacy that could be attained, given various constraints such as those listed above.