A heat lamp is an incandescent light bulb that is used for the principal purpose of creating heat rather than visible light. By operating the filament at a lower temperature, the spectrum of black body radiation emitted by the lamp is shifted and to produce more infrared light. Many heat lamps include a red filter to minimize the amount of visible light emitted. Heat lamps are commonly used in shower and bathrooms to warm bathers and in food-preparation areas to keep food warm before serving. They are also commonly used for animal husbandry. Lights used for poultry are often called brooding lamps. Aside from young birds, other types of animals which can benefit from heat lamps include reptiles, amphibians, insects, arachnids, and the young of some mammals. The sockets used for heat lamps are usually ceramic because plastic sockets can melt or burn when exposed to the large amount of waste heat produced by the lamps, especially when operated in the "base up" position. The shroud or hood of the lamp is generally metal. There may be a wire guard over the front of the shroud, to prevent anything from touching the hot surface of the bulb. Ordinary household white incandescent bulbs can also be used as heat lamps, but red and blue bulbs are sold for use in brood lamps and reptile lamps. 250 watt heat lamps are commonly packaged in the "R40" (5" reflector lamp) form factor with an intermediate screw base.