Optimum symmetrical light distributions

Certain symmetrical light distributions described briefly by the author in a previous paper are here considered at greater length. They possess, among other properties, that of producing uniform illumination on the horizontal plane in large lighting systems. The effect of varying the spacing/height ratio in a given system is here dealt with. Alternative methods of testing lighting fittings are described. The conclusion is reached that these light distributions may in some cases be regarded as the best that could be employed in practice, and in others as approximately the best. It is pointed out, however, that uniformity of illumination is often only one of a number of requirements that have to be met, and practical light distributions may be modified by this consideration and by the desirability of obtaining a high luminous efficiency.