Which of the following best describes T8 lamps?

T8 lamps are indeed characterized by their diameter, which is one inch. This specification is part of a standardized naming convention for fluorescent lamps, where the "T" indicates tubular and the number following it refers to the diameter in eighths of an inch. Therefore, a T8 lamp is 8/8 inches, or one inch in diameter, making this the definitive and correct descriptor.

The other options do not accurately represent T8 lamps; for example, T8 lamps have a much longer average lifespan than 1,000 hours, typically ranging from 7,000 to 15,000 hours. They are also commonly used in commercial settings rather than being exclusive to residential use. Additionally, T8 lamps do not contain halogen technology; instead, they utilize fluorescent technology.