Natural Outdoor Lighting Improves Contrast Sensitivity

Article: Pivotal vision study sheds positive light on the benefits of reading outdoors
Source: State University of New York, Optometry
Published: February 2, 2021

Graphical abstract: light-dark contrasts
were largest in bright environments

Contrast sensitivity is a measurement of luminance or color differences between the foreground and background of an object. In natural settings, it can affect visual function in situations of low lighting, glare, or fog, when contrast between the object and the environment is reduced. First author of the study explains, "Until now, vision research has operated under the assumption that luminance contrast does not change with light intensity. That is, a dark letter on a white page has the same contrast outdoors (under the brightest light) than indoors (under the dimmest light). Our study shows that this decades-old assumption is incorrect. We demonstrate that contrast sensitivity is strongly dependent on the amount of light and that natural, bright light stimulates the visual brain more effectively and improves eyesight.” The study, conducted in cat animal models and human subjects, showed  that "[as luminance range increases, contrast sensitivity increases more within cortical pathways signaling lights than those signaling darks. Conversely, when the luminance range is constant, light-dark differences in contrast sensitivity remain relatively constant even if background luminance changes." These differences in light-dark contrasts were largest for bright environments. They highlight that understanding that luminance settings affect visual contrast would reduce critical errors in research methodology and clinical care as well as improve cortical sensitivity that may help with better eyesight. Lead author of the study remarks, "The hope is that our study will serve as a catalyst for further investigation of contrast sensitivity and its role in current measures for the evaluation, diagnosis, and treatment of eye disease."

My rating of this study: ⭐⭐

Rahimi-Nasrabadi H, Jin J, Mazade R, et al. "Image luminance changes contrast sensitivity in visual cortex." Cell Reports.  34(5):108692. 2 February 2021. https://doi.org/10.1016/j.celrep.2021.108692