The MH lamps emit light across the entire visible spectrum, but are considered a cool light, having a lot of blue. They have efficiencies of about 80 to 100 lumens per watt and are rated at about 10,000 to 20,000 hours of life. MH lamps require a ballast also. Because these lamps must be mounted in a specific orientation (vertical or horizontal) they are not used much in the chicken house, but have been used in warehouse areas and egg handling rooms, where ceilings are high and efficient, bright lighting is required. These lamps also have a warm up period of between 5 and 15 minutes to achieve full illumination.