If it is a window screen or the plexiglass/plastic cover they include with all fixtures then you are dead on!. The larger holes allow more in than they block so only a smaller amount is lost. The safety factor goes up with only the hardware cloth- protection from all bad critters.The reason I asked was it has been mentioned that UVB lights don't work well for Vitamin D production, when placed on screens. I guess the Sun's rays don't have this problem.