The variations in light energy we experience are huge. For example, the average luminance outdoors can be 100 million times greater during the day than at night. The luminance dynamic range at any moment can also be large, with contrasts on the order of 10,000:1 from highlights to shadows. Luminance levels can also change dramatically over time and from place to place. Vision functions over these variations through a variety of adaptation mechanisms, however vision is not equally good under all conditions. In particular, people with low vision (often the elderly and those with visual disorders), can be profoundly impaired by low intensity, high dynamic range, and rapidly changing luminance levels. Unfortunately, existing clinical vision tests are typically done at moderate, near-optimal levels and contrasts, and may therefore underestimate a person's impairments. The need to develop more comprehensive and meaningful tests of vision and visual impairment under realistic illumination conditions has recently been articulated by both the National Eye Institute and the National Research Council, however, the limited output characteristics of standard display devices has been a significant impediment to progress. The emergence of high dynamic range (HDR) displays presents unique opportunities to develop new tools for vision research and testing and to advance our understanding of the effects of illumination on vision and visual impairment. This paper outlines some of these opportunities and describes some initial work to evaluate the use of HDR displays in this area.