The FVA-UV fiber optic variable attenuator from Ocean Optics Inc. couples via optical fibers to spectrometers, light sources and other sampling optics to attenuate light at all wavelengths uniformly. It consists of an aluminum block with threaded ports that hold two fiber-coupled collimating lenses. The attenuator is placed between two light sources, and a wheel with an aperture that varies in width along the circumference is fixed between the lenses. Rotating the wheel varies the light transmitted through the fixture. A thumbscrew locks the wheel in place.