A Guide to Light Bulb Sizes, Types, Shapes, and Codes.
Light bulb codes use letters to indicate shape and numbers (measured in eighths of an inch) to indicate diameter—for example, an A19 is a standard household bulb measuring 19/8ths inches across. Different bulb types serve specific purposes: A-series for general household use, candle bulbs (B and C) for decorative fixtures, reflector bulbs (BR and PAR) for outdoor lighting, MR bulbs for focused spotlighting, tubular lights (T and LFL) for kitchens and garages, and globe bulbs (G) for aesthetic applications. LED bulbs offer the best efficiency and brightness compared to incandescent, CFL, and halogen alternatives.