Neewer&reg; Labs Optical Glass Triangular Prisms (1.18"/30mm sides), Set of 2 Prisms - 4" (10cm), 7.8"(20cm)Lengths Set includes 2 Prisms, 4"/10cm Triangular prism + 7.8 "/20cm Triangular prism Triangular prisms are used to disperse light, that is to break light up into its spectral components(the colors of the rainbow) Side Length: 1.18 inch / 3cm Material: optical glass