This handbook provides a number of practical designs which utilize a range of opto devices, from a filament bulb to modern infra-red sensors and emitters. There are plenty of designs which should appeal to those who like to experiment with electronic circuits, but all the projects are tried and tested, and have practical applications. The projects are divided into three main areas, which are as follows: projects that use infra-red detectors, photographic projects and projects that are based on modulated light transmission. All the circuits should be within the capabilities of anyone who has a reasonable amount of experience at electronics construction. The more simple designs are also suitable for beginners.