The document discusses the phenomenon of dispersion of white light and the visible light spectrum. It explains that when white light passes through a transparent medium, it splits into its constituent colors from red to violet due to dispersion. The range of the visible light spectrum is from 0.4 to 0.7 microns. It also defines primary colors as red, blue and green which when mixed together produce white light, and secondary colors as cyan, magenta and yellow which are obtained by mixing two primary colors. Complementary colors are pairs of primary and secondary colors that combine to make white light.