Radiator, thermogram footage. Thermography records the temperature of surfaces by detecting long-wavelength infrared radiation. The colours show variations in temperature. The scale runs from white (warmest), through yellow, orange, red and purple to blue (coldest). In this footage, the radiator is initially at room temperature. After being turned on, hot water flows into it and it radiates heat (bright yellow). Some of the surrounding objects also start to heat up.