The last decade has seen the universal application of personal computers to lighting engineering problems on a day-to-day basis. No longer is the power of the computer invoked just for that large prestige job, the computer is constantly in use in lighting engineering laboratories and lighting design offices. This means that many calculations that were previously impracticable are well within the reach of any engineer or, for that matter, any person who has access to an appropriate computer program. However, there can be dangers if the application engineer does not have a grasp of the underlying principles used in the calculation processes. In this book we set out to give the reader the mathematical background to the calculational techniques used in illuminating engineering and link them to the applications in which they are used. In addition, we give details of photometric measurements, as a knowledge of these is necessary to understand the origin of the basic data used in the calculations and to check that the calculated performance requirements are met. We hope, also, the material will be of use to those who wish to write their own computer programs, and that it will be of didactic value. To keep the treatment as concise.