The invention concerns a light source utilizing an array (20, 50) of light emitting elements (22). The elements may be light emitting diodes. A fresnel prism (32, 56) is disposed in front of the array to receive light from it. The prism serves to divert light from the array along a direction (28, 54) oblique to the array, the diverted light forming an output beam. The array has a depth. The output beam from the prism has a depth which, measured in the same plane as the array depth but perpendicular to the beam direction, is smaller than the depth of the array. Hence a deep array provides a shallower output light beam in a manner which is convenient with regard to packaging requirements.