T5 lamps are the latest and most energy efficient lighting technology obtainable in the fluorescent lighting industry.
They use 45% and 12% less energy than its T12 and T8 predecessors. The T5 lamp provides peak light output at 35 °C (95 °F) air temperature. (By contrast, the T8 and the T12 lamps provide peak light output at a 25 °C [77 °F] ambient air temperature.) The T5 lamp has a higher lumens-per-watt efficiency than a T8 lamp of about the same wattage, in a space where there is little or no air circulation.
T5 lamps are a popular energy-efficiency measure, due to their potential to cut energy use in lighting by more than 60%.
The T5 lamp has a low mercury content. Each new generation of fluorescent lighting technology, including the T5 generation, has been able to function with less mercury, but perform with the same or greater efficiency.
A fluorescent lamp’s “cold spot” is the area on the lamp where the temperature is at its lowest. This cold spot rises or falls along with the ambient temperature of the lamp. Unlike a T8 or T12 fluorescent lamp, where the cold spot is in the middle, in T5 lamps it is at the end, on the metallic cap, about 2 mm from the glass envelope.
T5 lamps generally last for 20,000 hours, as compared to T8 lamps, which last for 15,000 hours.
These differences in dimension prevent T5 lamps from being used as replacements for T8 and T12 lamps, unless the existing luminaires are electronically converted, via T5 retrofit conversion, to high frequency operation, so that they can accept the T5 lamps.