A lamp's light output rating expresses the total amount of light emitted in all directions per unit time. Ratings of initial light output provided by manufacturers express the total light output after 100 h of operation. The ratio of the light output of a luminaire to the light output of the same lamp-ballast combination without the luminaire. Luminaire efficiency accounts for the optical and thermal effects that occur within the luminaire under standard test conditions. A measure of how effectively an electric load converts power into useful work.
Power factor is the ratio of active power to the product of rms voltage and rms current.
For rapid-start lamps, the time from the onset of lamp current to the lamp arc's striking, during which the lamp electrodes are heated to ease starting. A group of phosphors containing rare-earth elements, used in fluorescent lamps to achieve high efficacy, good color rendering, and low lamp lumen depreciation. For a current or voltage wave, the ratio of the wave's harmonic content to its fundamental component, expressed as a percentage. High current THD can create distortion in the line voltage, which could interfere with the operation of other electrical equipment.