The Circular Fluorescent tube is ring-shaped energy saving light bulb. The slim and compact light source that was designed for shallow and slender recessed, ceiling and wall mounted light fixtures. Circular fluorescent lamps will only fit into existing Circular fluorescent tube fixtures. And one wattage is one size. The Circular Fluorescent Tube is a uniquely shaped light source that comes in T5 (15mm diameter), T6 (20mm diameter) and T9 (29mm diameter) formats. The fitting comes in G10q, 2GX13, and more.