Dictionary
visible light
In astronomy, the word light is often used to denote any kind of electromagnetic radiation, from infrared radiation to X-rays and beyond. If, in contrast, an astronomer is talking about the ordinary light to which our eyes are susceptible – electromagnetic radiation with wavelengths between about 400 and 700 nanometers (400 to 700 billionths of a metre) – he or she will use the expression “visible light”.