Investigations on the Optimal Illumination of Viewing Cabinets

H a n s e n and E r l i n g R a t j e nDiagnostic radiology confronts its practitioners with two main tasks: (a) the production of a technically satisfactory radiograph, (b) its interpretation (if necessary in conjunction with fluoroscopy).In this paper we shall deal with a common factor in the interpretation of the radiograph, namely the luminosity of the viewing cabinet.I n outline it may be said that the reading of a roentgen film consists in appraising a visual impression.It is evident that a correct diagnosis is facilitated if the visual impression be an optimal one.Appraisal is a complicated, superior cerebral function which need not be discussed in detail.Visual impression is based upon two fundamental qualities of the visual senses: 1) the power to apprehend light (or the contrast sensitivity), and 2) the resolving power of the eye.The third quality of the eye, the ability to appreciate colours, has up to now not been called much into play in this connection.I n ordinary diagnostic radiology (macro-roentgenology) the contrast sensitivity is of more importance than the resolving power of the eye, provided the brightness of the film be not too low.Of the compound functions of vision derived from the contrast sensitivity and the resolving power of the eye, the ability to estimate thicknesses of lines and vernier acuity (CLEMMESEN, 1944) are of special interest to radiologists.Owing to the continuously and large output of processed films in the modern roentgen department, many different sizes and various degrees of density have to be put up in viewing boxes a t the same time.The density (D) is D = log I,/I (where I, is the intensity of the source of light and I the intensity immediately behind the film).For this reason many _ _