Figure 4.

Grating visual acuity for darks and lights measured under low luminance (maximum: 0.0312 cd/m²). (a) Grating visual acuity measured in two different subjects (left: S1; right: S2) as a function of spatial frequency and presentation time. Light targets were presented on dark backgrounds (red) and dark targets on light backgrounds (blue). The mean luminance was reduced by four log units with a neutral-density filter placed in front of the eye (moon icon). (b) Same as (a), but for gray backgrounds.