[4.2.1] In the physical space in front of the eye, one can identify points, lines, surfaces, and three-dimensional arrays of scattering particles that constitute the distal physical stimuli that form optical images on the retina. Each element of a surface or volume to which an eye is exposed subtends a solid angle at the entrance pupil. Such elements of solid angle make up the field of view, and each has a specifiable luminance and chromaticity. Points and lines are specific cases that have to be dealt with in terms of total candlepower and candlepower per unit length. Distal stimuli are sometimes referred to simply as lights or colors.

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