Identifying Fluorescent Lamps/Tubes/Bulbs
Fluorescent lamps, also known as bulbs or tubes, are identified by a series of letters and numbers imprinted on one end of the bulb that look like this: F40T12. Its very important to match a replacement lamp with the same wattage and diameter of a known working bulb, for in many cases the replacement is not directly compatible with the ballast, or will not work at all. Determine your lamp type before you order.
Here’s a breakdown of what the code means:
F – Stands for “Fluorescent.”
40 – Refers to the wattage. In this case 40W.
T – Stands for “Tubular,” meaning the shape of the lamp.
12 – Refers to the diameter of the tube in eighths (1/8) of an inch. In this case, 1.5 inches. (12 / 8 = 1.5)
Note that nowhere in the code does it specify its length. Simply use a tape measure to figure bulb length from tip to tip. However, do NOT use this length as the only determining factor of the lamp you choose.
So a F15T8 tells us it’s a 15 watt tubular fluorescent bulb with a diameter of 1-inch. Blacklights also have an additional designation of "BLB" appended to the code. The “BLB” stands for “Black Light Blue,” which tells us it’s a black light lamp using a special blue filtered glass, also called “Woods Glass.” There are also other designations for different kinds of output, such as "BL" for unfiltered UVA black light or “R” for red light.
About Fluorescent Ballasts
What is a ballast? In a fluorescent lighting system, the ballast regulates the current to the lamps and provides sufficient voltage to start and run the lamps. Without a ballast to limit its current, a fluorescent lamp connected directly to a high voltage power source would rapidly and uncontrollably increase its current draw and blow.
Because common fluorescent lamp types require a matching ballast, you will need an F32T8 ballast to run a F32T8BLB lamp, or F40T12 ballast to run a F40T12BLB lamp, or F54T5 ballast to run a F54T5BLB. Your lamp may be different from those mentioned here and would require a different matching ballast. The easiest way to determine the ballast type from an existing fixture is to identity the code on a known working bulb from that fixture; i.e. F40T12 (see above). Of course, you can always locate the ballast positioned inside the fixture and retrieve the code directly from it.
Note that ballasts may be rated to work on multiple lamp types. For example a ballast may be rated to light four F40T12BLB lamps, but only three F32T8BLB lamps and would not light four F32T8BLB bulbs. It is essential you are familiar with what your ballast can do and the proper lamp and quantity to use for the ballast.