Luminous efficacy measurement of solid-state lamps

We present a system for luminous efficacy measurements of solid-state lamps (SSLs). It is based on a 1.65 m integrating sphere, originally designed for luminous flux measurements of dc-operated incandescent standard lamps. The sphere was slightly modified, and equipped with a programmable ac-power supply, as well as equipment for electrical power measurement of the lamps. The waveforms of both the electrical power and the luminous flux can be measured for analysing the quality of the electronics and the light produced by the SSLs. A goniospectrometer is used for angular characterization of the lamp intensity. Luminous efficacy test measurements were conducted for a group of 25 SSLs of different types. Special attention was paid to the spectral, spatial and self-absorption corrections to obtain low measurement uncertainty. The luminous efficacies were between 25 lm W⁻¹ and 64 lm W⁻¹, and the total harmonic distortions of the current waveforms were in the range of 30% to 280%. Depending on the lamp, the maximum deviation of the flux from its mean value was 0.06% to 105%. The relative expanded uncertainty obtainable for the luminous efficacy of a typical SSL with stable built-in electronics is 1.2% (k = 2).