Abstract
Purpose :
Illumination variation in an indoor space might affect the visibility of architectural features such as steps and ramps. Poor visibility of these features can pose mobility hazards for people with low vision. This study examined the effect of typical variation in illumination level in an indoor space on the visibility of steps and ramps for observers with low vision.
Methods :
Five structures (Step Up, Step Down, Ramp Up, Ramp Down and Flat Sidewalk) were constructed in a large windowless classroom and presented one at a time as the target. The target had either a high contrast (79% Michelson contrast) or a low contrast (17%) against the background. The room was illuminated by overhead fluorescent lights which provided an illumination level of 800 lux. Viewing was monocular and the subjects wore goggles fitted with neutral density filters to attenuate light transmission, effectively producing three levels of photopic illumination: 800, 80 and 8 lux. 12 subjects with low vision due to various diagnoses (age: 21-75, logMAR acuity: 0.42-1.86) completed a 5-AFC task to recognize the target on each trial and gave a confidence rating on a 5-point scale. Acuities and contrast sensitivities of the subjects were also measured at each illumination level.
Results :
There was a weak but significant effect of illumination level on acuity and contrast sensitivity. With the decrease in illumination, visual acuity deteriorated by 0.11 logMAR on average over the illumination range tested and the Pelli-Robson contrast sensitivity decreased by 0.27 log unit. Recognition accuracy (percent correct) was not affected by target contrast nor by illumination level. However, there was a significant effect of target contrast on confidence rating: subjects were more confident about their judgments for high-contrast targets than for low-contrast targets. There was also a significant effect of illumination level: subjects became more confident about their judgments as the illumination level increased.
Conclusions :
Illumination variation over a typical photopic range in an indoor space had minimal effect on the visibility of steps and ramps for people with low vision. However, both target contrast and illumination level affected subjects’ confidence in their judgments. Subjective judgments of the accessibility of an indoor space may be more sensitive to design parameters such as contrast and illumination than objective performance measures.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.