Glare Characteristics of Lenses and Optical Instruments in the Visible Region

An automatic laboratory glare photometer has been constructed and used to measure the glare characteristics of some typical lenses, and a focal systems by the elementary source method. From the glare distributions produced by the instrument, the concept of a glare spread function (g.s.f.) has been developed and it has been shown that the use of g.s.f.'s permits the glare characteristics of an optical system to be expressed in a manner more basic than has hitherto been possible. The numerical values of the g.s.f. depend only on the system under test and not on the geometry of the test equipment. Glare spread functions can be useful in several contexts. They can be used as procurement standards prior to design or manufacture and the measured g.s.f.'s of existing instruments can be used to calculate glare distributions in particular situations, different from the one actually used for the measurement.