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Abstract
A new instrument is described for the measurement of equivalent sphere illumination. A basic optical system formed by the visual target and telephotometer is usually used for luminance contrast measurements. It is shown that this optical system can be replaced by an ordinary illuminance meter, the angular response of which is changed to mimic that of the bidirectional reflectances of a visual target's background and task. Moreover, a technique is described for producing a set of variable transmittance enclosures that are placed over an illuminance meter to give it the appropriate angular response. A combination of computer plotting and photographic techniques is used to generate enclosures that have transmittances which vary in the appropriate fashion. Successful operation of the new device is demonstrated.