Ultraviolet: Is ultraviolet invisible?
Answer: Yes, Ultraviolet at 397nm as well as infrared at 700nm are beyond human visions normally. Some birds and animals however can perceive some of these shorter and longer wavelengths. Many modern spectrophotometers identified as UV/VIS have an observation range from 200nm to 700 to 1,000nm (I micron). All Ultraviolet light is considered dangerous for the eyes and skin. The shorter the wavelength however the more UV is unable to penetrate, firstly acrylics, ordinary glass and then pure quartz at 200nm beyond 200nm and shorter, even water molecules and the air will block UV and can only traverse through a vacuum, i.e. ‘Vacuum UV’.