The sender is optimized for POF (Plastic Optical Fiber) and larger core multimode applications. The sender has a 665 nm universal connector and a 850 nm ST, SC, FC connector. The light source is designed for performing insertion loss measurements on fiber optic links when used with an optical power meter. Whether testing outside plant or premise an optical source is the perfect tool when combined with an optical power meter. The output is stabilized to ensure accurate test results per current TIA/EIA requirements. The wavelengths are individually adjustable with a mechanical screw to have a variable attenuator or to reduce the output power. This make it able to save battery power when high optical output power is not necessary, or to turn up the power to test long runs. This unit is easy to operate with only a wavelength/power switch, which selects optical wavelengths or disables the unit. The sender is delivered in a protective rubber boot.