This is a frequently asked question. I will explain size of lamp (bulb), wattage of each lamp, lumen output, energy savings and equivalent lighting fixture (how many lamps are equal to the same output).
Size of Lamp
T5s and T8s vary in length, but for this article I will be discussing T5HOs and T8s for 4 foot fluorescent fixtures. T5 or T5HOs are measured in metrics and are slightly shorter than 4 feet (or about 46 inches long). A T5 fixture will usually measure 4 feet and the difference in size of the lamp will be made up by extended sockets. T8 lamps measure 48 inches from the ends of the pins and will fit a 4 foot fixture perfectly. The diameter of a T8 lamp is 1 inch. The diameter of a T5 lamp is 5/8 inch.
As stated above, T5s vary in size, which will also vary the wattages for the lamps. T5 4 foot lamps vary from 28 watt non high output to 54 watt high output (and the new 49 watt t5 or T5HO lamp). T8 lamps also vary in size and associated wattages. Lamps for a 4 foot light fixture range from 24 or 26 watt reduced energy bulb to 32 watt standard output. Lumen output is controlled by the ballast.
- A T5 28 watt lamp equals about 2800 Lumens per lamp position
- A T5HO 54 watt lamp equals about 5000 Lumens per lamp position
- A T8 32 watt lamp with a low power factor ballast equals about 2100 to 2300 lumens per lamp position
- A T8 32 watt lamp with a normal ballast factor ballast equals about 2500 to 2700 lumens per lamp position
- A T8 32 watt with a high ballast factor ballast equals about 2800 to 3000 lumens per lamp position
When comparing equal lumen output vs. watts spent for T8 and T5 lamps, T8 lamps were 3% more efficient than the T5 lamps.
Using all the above information, here is a fixture comparison:
- A 4 lamp 54 watt T5HO high bay fixture has a 20,000 lumen output compared to a 6 lamp high ballast factor T8 32 high bay fixture which equals 18000 lumens
- A 6 lamp T5HO fixture approximately equals the output of a 400 metal halide fixture (when new before the 3 year diminish).
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