This is a 12W fluorescent ring bulb.
It fits the 12W microscope fluorescent ring lights with Model FRL12.Features & SpecificationsPower: 12WVoltage: 110V/220VType: fluorescent ring bulbInner Diameter: 3-1/16" (78mm)Outer Diameter: 4-1/16" (103mm)Manufactured under ISO 9001 Quality Control Standards.12W Fluorescent Ring Light Bulb It comes with 78 mm inner diameter and 103 mm outer diameter.