The ray box can be used in a single-ray mode without using the plano-convex lens. However, with the lens inserted (plane face towards the light source), and using the two-slit, three-slit or broad-slit masks, the emergent light can be made to be divergent, convergent or parallel by adjusting the position of the light source in relation to the lens. These facilities enable the ray box to be used in a wide range of optical experiments with transparent flat based blocks, prisms and mirrors. The coloured filters can be used to produce beams of coloured light, but external light levels have to be reduced for maximum effectiveness. Base measurements: 180 x 65 x 75mm. The light source is mounted under an adjustable lid, designed so that minimum light emerges in unwanted directions. Power requirement: 12V (AC or DC) connected to two 4mm sockets on the ray box. Light source: 12V, 21W lamp fitted in brass holder with one meter twin flex having banana plugs. Accessories: Plano-convex lens of focal length 75mm; 2 plastic masks with, respectively, one and two thin slits, three thin slits and one broad slit; 7 coloured filters and 1 tri-colour filter, mounted in 50 x 50mm plastic frames; 1 spare 12V 21W bulb.