Visual display unit research. Physicist using a spectroradiometer to analyse the luminance of a VDU (visual display unit, also known as a computer monitor). Spectroradiometers measure the range of electromagnetic radiation emitted by an energy source. Electromagnetic radiation takes the form of visible light, ultraviolet light, infrared light, microwaves, radio waves, gamma rays and X-rays. There have been concerns that electromagnetic radiation from some electrical devices may cause negative health effects. Although these are unproven, it is necessary to check that the energy output is at a level considered safe for users. Photographed at the National Physical Laboratory in Teddington, UK.