Visible radiation is perceived by humans in the form of light, but there is also radiation that is invisible to humans in other wavelength ranges. Every body radiates heat (energy) in the form of light sources. Thermal imaging cameras are used to detect these infrared rays, which are invisible to humans. The thermal imaging device uses a sensor that measures the infrared radiation emitted by bodies and objects. This converts thermal radiation into an image. The image generated shows the correct outlines but not the original colours of the body or object. The greater the temperature differences and the warmer a body is, the easier it is to recognise and make visible. Thermal imaging cameras do not need light to create an image. With a thermal imaging camera, you can visualise the temperature of everything you can see on a normal digital camera. Infrared radiation does not pass through solid matter or panes of glass so you cannot see through these with thermal imaging cameras. You also cannot distinguish between lighter and darker appearances.