In 1666, Newton discovered the spectrum and measured that 3,900 ~7,600 (400nm~700nm) was the wavelength of visible light. William Herschel, Royal Society of London, April 24, 1800 published sunlight In addition to the red light of the visible spectrum, there is an invisible extension spectrum with thermal effects. The method he used was simple, using a thermometer to measure the temperature of the light after the prism was divided, from purple to red, and found that the temperature was gradually increasing, but when the thermometer was placed outside the red light, the temperature continued to rise, and it was concluded that there was an infrared presence. The same tests were done in the ultraviolet part, but the temperature did not respond to increased. Ultraviolet light was discovered in 1801 by Ritter with silver chloride chloride photosensitive agent.