I've been doing that very thing, and I'm not sure how cold the air would have to be for that to be a negative instead of positive. All electrical equipment will perform better longer in cooler conditions. I guess if the cold air lowered the temp in your grow enough it could affect your plants, but it can't be anything but good for the light. Keep in mind that that outside air will be really hot in the summer, which won't provide much cooling, and may exacerbate heat issues. I've got 3200 watts of lighting, so that cold air (which has gotten down below 0 in the last month) only got my flower room temp down to 59. Good luck.