The Eye, Brightness and Illuminating Engineering

The great interest now being evinced in brightness engineering makes it desirable to review the basic facts concerning the quantity brightness and its rôle in vision, to inquire whether the properties of the eye suggest any desirable limitations on brightness or brightness ratios in the field of view, and to examine the suitability of brightness as a quantity in terms of which to couch illuminating engineering specifications. The importance of brightness in vision rests essentially on the fact that the illumination of the retina of the eye is proportional to the brightness of the object viewed, although a closer examination of the eye shows that the connection is not quite so simple. Again, the way in which radiations of different wavelength contribute to brightness under different eye conditions raises difficulties. Despite the considerable knowledge that exists of the response of the retina to light, it is by no means easy to deduce clear guiding principles to assist the illuminating engineer, and for some years the latter has had resort to the results of more ad hoc studies. It is always well, however, to take stock of fundamentals from time to time, and the present paper is an attempt in some measure to do this.