UPSC 2017 CDS I GK Paper

Among the given wavelengths, third item, i.e., 500 nm only can make visual sensation to a human eye. Visible light is the only light detectable by the human eye. White light is visible light, and it contains all the colours of the rainbow, from red to violet. The range of visible wavelengths is 400 nanometers to 700 nanometers.