Abstract
An eight year program of research is reported here which has led to the development of a general method by which illumination levels may be determined for various practical tasks, based upon visual performance criteria. The present report contains the following sections: I. Characteristics of visual performance. II. Laboratory performance data for standard disc targets. III. Field factors. IV.The visual task evaluator. V. The standard visual performance curve. VI. The standard lighting specification procedure. VII. Evaluation of sample visual tasks. VIII. Future developments of the method.