Lamp Guide: Fluorescent by Brandy McNeilin GuidesFebruary 17, 2017 Miniature Bipin T-5 Min. Bipin Medium Bipin T-8/T-10/T-12 Med. Bipin Recessed Double Contract T-8/T-12 Recessed D.C. Slimline Single Pin T-8/T-12 Circleline 4-Pin The size and shape of a bulb is designated by a letter or letters followed by a number. The letter indicates the shape of the bulb while the number indicates the diameter of the bulb in eighths of an inch. For example “T-10” indicates a tubular shaped bulb having a diameter of 10/8 or 1 1/4 inches. The following illustrations show some of the more popular bulb shapes and sizes. The size and shape of a bulb is designated by a letter or letters followed by a number. The letter indicates the shape of a bulb while the number indicates the diameter of the bulb in eighths of an inch. For example, “T-12” indicates a tubular bulb having a diameter of 12/8 or 1 1/2 inches. The following illustrations show some more popular bulb shapes and sizes. T-5 Miniature Bipin T-8 Medium Bipin T-10 Medium Bipin T-12 Medium Bipin T-8 Recessed Double Contact T-12 Recessed Double Contact T-12 Recessed Double Contact (Jacketed) T-8 Single Pin Slimline T-12 Single Pin Slimline T-8 Medium Bipin U-Bent Lamp T-12 Medium Bipin U-Bent Lamp (6″) T-12 Medium Bipin U-Bent Lamp (3″) T-9 4-Pin Circline Earth Light Lamps SL/O SL/T SL/R40 SLS/G40 SLS 9,11 SLS 15,20,23,25 SLS/R30, R40 PL Lamps PL Adapter System (First 2) PL-S/SYS PL-C/SYS PL-S PL Replacement Bulb (All 3) PL-C PL-L PL-T