Light Box Kit part, SET/3 slit formers. NOTE: These are not available individually, a set of 3 must be purchased. The slit patterns are: 1 slit / 3 slits, 4 slits / wide slot, 2 slits / blank end. The slits are used to create narrow light rays. The wide slot is used with a prism to create the spectrum (rainbow) of colours. The 'blank end' is used for shutting off the light.