Fluorescent Lamps:
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The most common shape is a straight tube. This bulb, has a smooth surface and comes in a number of sizes. The diameter of the glass tube is measured in 1/8ths of an inch and is used in many fluorescent descriptions: for example, T12 fluorescent lamp is 12 eighths of an inch or 1-1/2” in diameter, T8 lamps are 1 inch in diameter, T5 lamps are 5/8th of an inch in diameter..

The grooved surface of the GE Power Groove® bulb provides greater tube surface for a given length, increasing light output.

A standard fluorescent tube bent into a "U" shape, named the Mod-U-Line®, offers mounting alternatives. For example, a standard U-shape can mount in a two foot by two foot ceiling fixture compared to the two foot by four foot fixture required for straight lamps.

Fluorescent lamps are also available in a circular bulb, called the Circline