This International Standard adopts both the veiling glare index (VGI) and the glare spread function (GSF) as measures of the veiling glare characteristics of optical and electrooptical imaging systems. Laboratory measurement techniques are described in general terms and recommendations are made regarding the performance of the main subunits of the equipment.

The measurement techniques described in this International Standard are chiefly valid for the visual spectral range. For adjacent spectral ranges, modifications of these techniques will possibly be necessary.

Standard methods of specifying conditions of test and of expressing the results are given, while to assist in the intercomparison of VGI figures, standard test conditions are specified.

This International Standard also gives guidelines for the operation of measuring equipment such that accurate results can be achieved.

Results of veiling glare index measurements made using equipment which does not conform in detail to the configurations described in this International Standard are accepted as valid, provided the method of measurement is substantially similar (i.e. measures the ratio of the radiance in the image of the black area to the radiance in a surrounding bright field) and provided the test results can be correlated to the required accuracy with results obtained on equipment which conforms strictly to this International Standard.