Underwater lighting 457 Shooting in the rain In addition to providing GFCI protection one of the primary concerns when shooting in the rain-- real or artificial--is that the lights are protected from falling and blowing moisture. If water falls or blows onto the hot lens, the thermal shock can crack or shatter the lens, especially when the bulb is in flood position, where it makes the lens hottest. If water leaks into the housing and touches the globe, the globe will burn out or explode. With HMIs, water causes serious problems with the elec- tronics. Water can also cause corrosion to the metal parts of the fixtures. Some lights are designed to shed water to some degree while most are not (see Appendix E). Protect the lens with a gel frame of heat-shield gel or a thin color ( CTO or CTB). Place rain hats over the lights. Rain hats can be made out of Celo screen (a tough, plastic-covered, wire screen); a flag covered with a garbage bag works for small lights; a four-by flag wrapped in Visqueen for bigger lights. Poly Storm is a special material that can withstand extremely high temperatures. It is ideal for rain hats, because it is not prone to melt or catch on fire like Visqueen-covered flags. A 12-by or 20-by griff is handy to cover a number of units at once. (Check for holes in the griff first.) Rain hats should be positioned so that rain runs off away from the fixture; don't let rain collect and form a pool in the flag. Lighting rain