Lighting Research Center Lighting Research Center
    Volume 6 Issue 1
July 2002    
Do T5 luminaires perform better than T8 luminaires?

T5 lamps differ in lamp size and optimal temperature from T8 lamps, and both these factors affect luminaire performance. The smaller lamp diameter of T5 lamps can increase optical control efficiency and flexibility of luminaires. The higher optimal temperature of T5 lamps may allow T5 lamps to perform better in closed luminaires than open luminaires, and the difference in optimal temperature complicates T5 luminaire photometry and other comparisons to T8 lamps.

How does temperature affect the performance of a T5 lamp?

T5 and T5 high output (T5 HO) lamps are designed to produce maximum light output at 35°C (95°F), while the light output of T8 lamps is optimal at a temperature of 25°C (77°F). Figure 10-1 diagrams the performance of T5 and T8 lamps as a function of ambient temperature. OSRAM SYLVANIA and GE Lighting also provide similar diagrams in their online catalogs. A recent study (Zhang & Ngai 2001), however, suggested that the difference in light output of T5 lamps between 25°C (77°F) and 35°C (95°F) is often smaller than the difference shown in Figure 10-1. Other uncontrollable factors might also influence the light output of T5 lamps. Figure 10-1 shows that there is roughly a 10% difference in light output for both T5 and T8 lamps between 25°C (77°F) and 35°C (95°F). The 10°C (18°F) difference in optimal temperature between T5 and T8 lamps may affect lamp performance in various types of luminaires.

Figure 10-1. Light Output and Ambient Temperature

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