Date of Award

August 2021

Document Type


Degree Name

Master of Science (MS)


Applied Psychology

Committee Member

Richard A Tyrrell

Committee Member

Benjamin R Stephens

Committee Member

Zhuo Job Chen


Typical road users appear not to understand retroreflectivity despite nightly exposure to retroreflective materials such as road signs. While retroreflective surfaces have been engineered to reflect light back in the direction of its source, retroreflectors appear to be diffuse reflectors in most viewing conditions. This may lead road users to underestimate its value in nighttime roadway applications and contribute to vulnerable road users’ under-use of retroreflective markings to enhance their own conspicuity at night. In this context, a critical benefit of retroreflective materials is a robustness to changes in entrance angle, the angle at which the light strikes the material.This online study measured participants’ perceived brightness judgments for surfaces that represent three types of reflection (diffuse, specular, and retroreflective) with varying entrance angles. To assess the potential benefits of seeing retroreflectivity in action, perceived brightness was evaluated before and during a demonstration that includes illumination from a directional light source positioned near the recording camera. After seeing the visual demonstrations, participants’ brightness judgments revealed an enhanced appreciation that retroreflective (but not specular or diffuse) surfaces remain bright despite large changes in entrance angle. These findings could be utilized to design more effective and accessible video demonstrations of retroreflectivity in hopes of increasing the demand for retroreflective markings by vulnerable road users.



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