Hot drink. Thermogram of a woman in bed, being given a hot drink containing a treatment for her cold. The colour-coding shows variations in temperature. The scale runs from white (warmest), through red, yellow and green to blue (coldest). Thermography records the temperature of surfaces by detecting long-wavelength infrared radiation. The drink (upper centre, white) is hot, as is the woman's face, probably indicating an elevated body temperature as her body attempts to fight off her illness. The bedclothes are blue, because they provide insulation and do not efficiently transmit heat.