A choice of filters is available: blacklight (UV100) or ‘uv-blue’ (UVV80). The black filter eliminates visible light above 405nm, which gives superior fluorescent contrast. The optional blue filter passes slightly more UVA plus a lot of blue light up to 450nm. This volume of blue increases fluorescence of some tracer liquids, but also reduces the visual contrast. This can be corrected by using yellow tinted UV protective spectacles (UV1102Y - included in each kit), which will cut down the blue reaching your eyes.