Thermoelectric coolers are solid-state heat pumps used in applications where temperature stabilization, temperature cycling, or cooling below ambient levels are required. Thermoelectric cooling is produced when direct current (DC) is applied across two dissimilar materials and causes a temperature differential. Because of their relatively low efficiency, thermoelectric coolers are used mainly in environments that require solid-state devices. Typically, a thermoelectric cooler is used for a job that would be impractical with a compressor-based system.