Overhead warmers are best used to keep food warm for a short period of time. They generally have toggle switches that simply turn them on and off or allow you to go from low to high heat; therefore you won’t have much control over the temperature.
Heat lamps - also known as bulb warmers - use an infrared bulb, a heated metallic rod or a heat panel. The traditional glass or quartz bulb heat lamps have the advantage of putting out some light in addition to heat. Typically, bulbs are used for spot warming of individual pans of food and therefore work well in buffet or self-service scenarios. The disadvantage to bulbs, besides warming only one spot, is they tend to break easily.
Heat Strips sit above a shelf and cover the length desired with even heat. The units have the advantage of coming in a variety of lengths, from about 18 inches to 12 feet. The rod-type warmers are high-powered and generate a lot of heat. Most models spread heat to cover a shelf with even, intense heat and are mounted 12-18 inches above the food.