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Young and Old Eyes
APPALLING PREVALENCE OF EYEDEFECTS
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100 footcandles 12-point type 14 inches 8-point actually adequate artificial light average normal vision barely visible black object blink-rate brightness brightness-contrast brightness-level brightness-ratio candles per square Chapter chart color contrast critical details critical tasks dark daylight decrease diffuse reflection-factor diffusely reflecting effects energy example eye-defects eyeglasses eyes eyesight specialist fact factors factors of safety fluorescent lamps footcandle-levels glare glare-source gray human seeing-machine increases involved letters level of illumination light and lighting light-sources lighting practice lumination Matthew Luckiesh measurements minutes near-vision obvious outdoors performance poor seeing conditions printed matter pupil relative visibility researches retina reveal safety see-level seen Snellen chart socalled spectral specular reflection square inch standard of visibility surface surroundings test-chart test-object threshold tion tungsten-filament type-size varies various viewpoint visibility and ease visibility meter visual acuity visual angle visual efficiency visual field visual sense visual task white background white paper