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Quan Lei, Brent Carpenter, Daniel Kersten, Gordon E Legge; Visibility of Steps and Ramps in Natural Lighting: Effects of Simulated Loss of Acuity and Contrast Sensitivity. Invest. Ophthalmol. Vis. Sci. 2018;59(9):3421.
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© ARVO (1962-2015); The Authors (2016-present)
Variations throughout the day in the pattern of natural lighting can affect the visibility of architectural features such as ramps and steps. Poor visibility of such features poses mobility hazards for people with low vision. The current study exploited the wide variations in natural lighting across a day and investigated how lighting interacts with reduced acuity and contrast sensitivity to affect the visibility of steps and ramps in a typical indoor space.
An indoor space with windows admitting natural lighting was rendered using the Radiance software to produce photometrically accurate images for different hours (8AM, 9AM, 12PM, 4PM, 5PM) of a day with different lighting patterns. One of five structures (Step Up, Step Down, Ramp Up, Ramp Down and Flat Sidewalk) was embedded in the scene as the target. These images were processed to simulate acuities of 20/20, 20/320, 20/640, and 20/1280, and contrast sensitivities of 100% (normal), 50%, and 25%. Thirty normally-sighted subjects completed a 5-AFC task to identify the target in each image.
Target visibility was affected by a significant interaction between target type, day hour, acuity and contrast sensitivity. Overall performance changed across the day; different targets showed performance peaks and troughs at different hours associated with variations in the lighting patterns. Uniform lighting (12PM) facilitated the recognition of the Flat target; different patterns of directional lighting facilitated the recognition of certain targets but impaired others. Performance for Step Down showed the largest variation across the day; directional lighting at certain hours (e.g. 4PM) showed beneficial but at other hours (e.g. 8AM) detrimental effects, depending on the alignment or misalignment of lighting patterns with diagnostic features for the step. The effects of lighting were particularly strong when acuity and contrast sensitivity were low and nearly absent when both were normal.
The pattern of lighting, in addition to overall level of illumination, can have an important effect on visibility due to variations throughout the day. Specifically, a down step, posing a serious mobility hazard, should receive special attention when exposed to natural lighting. Designs intended to enhance visual accessibility for low vision should attend to the potential variations in visibility throughout the day and year.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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