When:
2016-06-08 at 14:00
Where:
Conference room, UCL R+0, 13 rue Moreau, 75012 Paris
Details:
TITLE:
Light… what is it good for?
ABSTRACT:
Increased lighting is an intervention of choice recommended to patients with low vision. The effects of lighting on visual acuity have been repeatedly studied and demonstrates that acuity can be improved by increasing illumination under some conditions. However, the effects of lighting on detection and processing of supra-threshold text have not been thoroughly studied. The goal of our study was to quantify under what lighting and text conditions increases in lighting level will improve reading performance. Thirteen normally sighted subjects (<20/20) and nine individuals with vision loss (>20/200) due to non-exudative AMD participated in this study. Short sentences, printed at sizes ranging from 0.0 to 1.3 logMAR, were read aloud under luminance levels ranging from 3.5 to 696 cd/m2. Reading speeds, in words per minute (WPM), were calculated from the number of words read correctly based upon audio recordings. For control subjects, the effects of increasing luminance on reading speed varied depending upon the size of the text and on the relative changes in light level. When measured at a dim (mesopic) luminance level (3.5 cd/m2), reading speeds were slowest at the smaller letter sizes but reached an asymptote for larger letter sizes. When illuminance was increased to photopic levels, there were increases in reading speed at the smaller letter sizes, but no increase in speed at the larger letter sizes. Furthermore, increases in light level above 35 cd/m2 did not result in additional reading speed gains at any letter size. For individuals with AMD, the same relative effects of luminance were observed, although the positions of their text size versus reading speed functions were shifted to larger sizes and slower reading speeds. Our data emphasize the need to question the broad generalization that providing a brighter lighting to patients improves reading performance. Although performance on acuity-limited tasks may be improved by brighter lights, this effect is dependent on the relative changes in light level and text size. When recommending a lighting intervention, it is important to assess the parameters of the visual tasks that the patient wishes to engage in and the typical level of illumination used for those task in order to estimate potential gains from increased lighting.