What does the '8' in T8 lamps indicate?

The '8' in T8 lamps specifically refers to the diameter of the lamp in eighths of an inch. Therefore, a T8 lamp has a diameter of 8/8 inches, or one inch. This designation is part of a nomenclature system used to classify fluorescent tubes; the 'T' stands for tubular, while the number indicates the diameter in eighths.

Understanding this system is fundamental in selecting the right type of lighting for specific applications, as it helps differentiate between other types of fluorescent lamps, such as T12 (which is 12/8 inches or 1.5 inches in diameter) and T5 (which is 5/8 inches in diameter). This distinction affects compatibility with fixtures and the performance characteristics of the lamps.