Diffraction grating Rainbow Peepholes™ will provide great fun for the classroom to teach students about Light and Color. Look through the mini sized Rainbow Peephole™ at any light source and the rainbow starbursts will amaze you! 13,500 Line/Inch Diffraction Grating. 1-11/16" Diameter x 1/2" Window. Heavy Cardboard. Set of 50/pack. Plenty for a classroom with spares in case they get lost or damaged.