Where we are in light source performance; where we would like to get

Summary form only given. The 117-year history of the electric lighting industry has witnessed dramatic increases in light source performance, from 2-3 lumens of light per electrical watt of power input for Edison\´s carbon-filament incandescent lamp to 100+ lumens per watt for electric discharge sources today. Performance improvement has been in the main episodic rather than continuous, marked by factor-two (or more) increases over prior devices upon introduction of totally new light sources. The most dramatic gains have resulted from employment of electric discharges in gases as light sources. These combine the unique advantage of achieving a much higher radiating-source temperature than any solid object with the ability to tailor the radiation spectrum by selection of gaseous radiating species. Unfortunately, no such dramatically-new light sources have been discovered in the last quarter-century. This raises the question whether the industry has reached a thermodynamic limit. In this presentation, I discuss the twin components of light source efficacy; efficiency of conversion of electric power to radiant power, and the optimization of spectral power distribution of that radiant power to produce the maximum luminous flux consistent with "white light".