ABSTRACT
Photometric Units The formal name for the measurement of light is photometry. It is part of the wider system of measurement of electromagnetic radiation, which is called radiometry, but as it is concerned with visible radiation its units have to be associated with the visual process. In all aspects of imaging technology we need terms to define such matters as light sources, quantity of illumination, reflection, transmission, and so on, in terms that can readily be related to one another and to units of mechanical and electrical energy. In the past there were three different systems-FPS, CGS, and MKS-resulting in a proliferation of named units, to the confusion of students and the exasperation of their tutors. Unfortunately, some academic texts still employ these outdated systems. In this book I use only SI units, with the occasional centimeter or inch where either is obviously called for.
