T12 Vs. T3 Fluorescent Bulbs

Written by ronald bell
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T12 Vs. T3 Fluorescent Bulbs
Circular fluorescent bulbs utilise T3 tubing. (Cfl fluorescent light bulb on dark background image by Silverpics from Fotolia.com)

The "T" designation in fluorescent bulbs tells the consumer the diameter of the glass tube. The diameter does not relate directly to the brightness of the fluorescent bulb.


The T rating of a fluorescent bulb denotes the diameter of the tube in eighths of an inch. A T12 bulb would be 12/8 of an inch --- or 1.5 inches -- in diameter. The smaller T3 bulb would be 3/8 inch in diameter and the T8 bulb would have a 1 inch diameter.

Compact Fluorescents

Compact fluorescent lights (CFLs) have been the main driver behind the recent growth of T3 fluorescent tube products. The average life of a CFL is 10,000 hours while the life of a comparable light bulb is 1,000 hours.


The Environmental Protection Agency (EPA) encourages the use of CFLs but also warns us they contain mercury. An average size CFL contains 4 mgs of mercury compared to 500 mgs in the older types of oral thermometers. None of the mercury escapes into the environment unless the CFL breaks.

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