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The "White on Black" Slide

Samuel Packer, MD; James S. Robertson, MD, PhD
JAMA. 1972;221(10):1163-1164. doi:10.1001/jama.1972.03200230049018.
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To the Editor.—  Some lecturers use slides with white letters on a black background. Although this may appear at first glance to be more dramatic than the more standard black on white, the written material so presented is actually more difficult to read. "Snellen" acuity is in part due to resolution acuity, and the latter is decreased by irradiation (white letters spilling over into the black background). Thus, the decreased visual acuity in the white on black slide is in part accounted for by the optical problem of irradiation.The principal of irradiation and its relationship to visual acuity is explained in the text by Rubin and Walls.1Bright-on-dark resolution acuity is never very 'good.' Resolution charts and targets which are identical, except for being related to each other like a photographic positive to its negative, are consequently not interchangeable. The observer's performance will be poorer, other things being


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