Heat lamps are incandescent light bulbs that can be considered energy efficient because the heat they naturally produce is actually being utilized. There are a lot of applications for which heat lamps are needed, including showers and bathrooms, food preparation areas, animals/pets. Until recently I wasn't aware of just how widely heat lamps can be used!
Bathroom Heat Lamps
Light bulbs used as heat lamps work great in bathrooms, especially basement bathrooms in winter. It can get freezing cold down there in the morning! A heat lamp in the ceiling or above the mirror helps a lot in combating the frigid temperatures of a basement bathroom in winter. Heat lamps can include a red filter to minimize visible light production, but not all of them include a filter.
Heat Lamps for Pets
One area where heat lamps are actually mandatory is taking care of animals. Young birds, reptiles, amphibians, insects, arachnids, and many mammal babies need the additional heat when in the artificial environments humans create for them. These are the places where the red filter helps; you don't want to blind your pets! Heat lamps that are used for poultry are also known as brooding lamps.
Heat lamps most often come with ceramic socket bases, because plastic can easily melt or burn from the immense heat generated by heat lamps. The entire apparatus does not need to be ceramic however, and you will find plenty of heat lamps with metal shrouds/hoods. Most heat lamps I've seen have a wire guard in front of the light bulb to prevent touching the source of the heat.
Standard incandescent light bulbs can be used as heat lamps in a pinch. The main gripe conservationists have against incandescents (the wasted heat) can actually be a boon in some cases! Specialized heat lamps are red and blue, which are generally sold for use as brood lamps or reptile lamps.