In this issue of Lighting Answers, NLPIP summarizes information on thermal effects in 2-foot x 4-foot fluorescent lamp luminaire systems, reports the results of testing two types of recessed 2-foot x 4-foot luminaires with different combinations of fluorescent lamps and ballasts at different plenum temperatures, and describes how to account for the thermal effects in calculations of light output and energy use. Manufacturers usually publish luminaire performance data for given lamp-ballast-luminaire combinations operating at 25 degrees C (77 degrees F) ambient temperature. A fluorescent lamp's light output, active power, and efficacy, however, depend on the lamp's operating temperature. Thus, the performance of a luminaire when it is installed may differ from its rating, and manufacturers' ratings do not predict energy savings and light output accurately for many applications. |