4" Crystal Optical Glass Triangular Prism Refractor - Physics Teaching Light Spectrum Optics Kits 100mm &#10132; Triangular prisms are used to disperse light, that is to break light up into its spectral components (the colors of the rainbow). &#10132; Show a rainbow for you and your children. Buy it now, enjoy the fun of light &#10132; It is a good present for friends with gift box package &#10132; Prism Length: 3.94 inch / 10 cm, Side Length: 1.18 inch / 3cm &#10132; Material: optical glass, not plastic