Abstract: Optical scale reading apparatus in accordance with the invention includes an optical fibre 30 for directing light from a light source 22 on to a scale 10. Light from the scale is reflected into a readhead 12 of any suitable construction. The fibre is designed to reduce any non-uniformity in the light entering it and various embodiments of the invention are described for achieving the required effect. For example, the length to diameter ratio of the fibre is made to be at least 5:1. Alternatively, or in addition, one or more constrictions are formed in the fibre, and as a further alternative or addition, at least one end face of the fibre is roughened to cause diffusion of the light.