Volume 6 Issue 1
July 2002    
Do T5 lamps have better lumen maintenance than T8 or T12 lamps?

Lumen maintenance refers to how a lamp maintains its light output over its lifetime. Both T5 and T5 high output (T5 HO) lamps maintain a higher light output than T12 and most T8 lamps. Manufacturers claim that T5 and T5 HO lamps retain more than 95% of light output at 8,000 burning hours (40% of rated average life). An improved phosphor coating reduces mercury absorption, which is one of the main causes of lamp lumen depreciation, leading to a higher lumen maintenance value. Also, because the T5 is smaller in diameter, it has a much smaller surface area. Manufacturers use only tri-phosphors in the T5, compared to the T8 and T12, in which there may be a mix of tri-phosphors with halo-phosphors. Figure 9 illustrates lumen maintenance curves for T5, T8, and T12 lamps (see How long do T5 lamps last before they burn out? ). In Figure 9, T12 lamps are labeled as "CW/HO," which stands for cool white high output.

Figure 9. Lumen Maintenance Curves of T5, T8, and T12 Lamps as a Function of
Burning Time

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