Only to be used in the appropriate sealed unit for water or air purification.This is a 18W germicidal PLL light bulb that emits short wave ultraviolet UV-C radiation peaking at 253.7nm that kills bacteria and other microorganisms for use in pond filters killing algae or disinfection of drinking water, among other applications.These light bulbs must be used in an appropriate, fully enclosed fitting. They should not be used as a substitute for fish tank lights etc. or for the purpose of illuminating enclosed aquaria. Not suitable for household room illumination.Features a 2G11 4-pin oval base.Please read our guide for more information.WARNING: Germicidal lamps emit high-intensity UV-C radiation that can cause sunburn and conjunctivitis. The skin and eyes must therefore not be exposed to direct or reflected unfiltered radiation. They should only be used in the appropriate sealed unit for water or air purification.