Drying clothes. Thermogram of clothes on a household radiator. The colours show variations in temperature. The scale runs from white (warmest), through yellow, orange and red to purple (coldest). Thermography records the temperature of surfaces by detecting long-wavelength infrared radiation. The hot radiator shows up as bright yellow/white, in contrast to the cooler clothing. Note the water vapour seen rising off the socks at upper right (pale yellow).