The heaters have been built to use only as much power as necessary and thereby not waste energy. They have sponge insulation on one side to prevent heat being lost into the atmosphere. The heat is directed into the optics instead and because of this, less energy is needed to keep your optics moisture free. The heaters wrap around your objectives, label side out and are held in place by elastic/Velcro attachments. Telrad heaters are held in place with an elastic band. The heaters for secondary mirrors are placed on the backside of the secondary and can be held in place by using the polyester batting found inside the secondary mirror holder. The .965/1.25", 1.25/2" and 2" are considered eyepiece heaters. The 1.25/2" and 2" are also heaters for camera lenses and certain binoculars.