A rectangular light fixture that fits into a dropped ceiling is usually designed for which type of bulb?

The correct answer is T12. Rectangular light fixtures that fit into dropped ceilings are typically designed for fluorescent tubes, and T12 refers to a specific type of fluorescent tube with a diameter of 12/8 inch (1.5 inches). These tubes are commonly found in commercial lighting applications and are suitable for being mounted in the type of fixtures used in dropped ceilings.

T12 bulbs have been a standard in commercial lighting for many years, particularly before the advent of more energy-efficient options. While other bulb types, such as MR 16, PAR 20, and LED PAR 30, can sometimes be used in certain lighting applications, they do not typically fit the rectangular lighting fixtures designed specifically for installed fluorescent tubes in ceiling tiles.

In summary, T12 is the best answer because rectangular fixtures in dropped ceilings have traditionally utilized T12 fluorescent tubes, catering to both practical considerations and common installation practices in commercial settings.