I just installed a couple of these in a metal box on the mill. They are very bright, waterproof, rugged, and cheap.
http://www.homedepot.com/Lighting-Fans-Outdoor-Lighting-Outdoor-Lighting-Accessories/h_d1/N-5yc1vZbvlv/R-202266480/h_d2/ProductDisplay?catalogId=10053&langId=-1&storeId=10051...