Side-by-side comparisons were made over solstice-to-solstice changes in sun and sky conditions between
an optical louver system (OLS) and a conventional Venetian blind set at a horizontal slat angle and located
inboard of a south-facing, small-area, clerestory window in a full-scale office testbed. Daylight autonomy
(DA), window luminance, and ceiling luminance uniformity were used to assess performance. The
performance of both systems was found to have significant seasonal variation, where performance under
clear sky conditions improved as maximum solar altitude angles transitioned from solstice to equinox.
Although the OLS produced fewer hours per day of DA on average than the Venetian blind, the OLS never
exceeded the designated 2000 cd/m2 threshold for window glare. In contrast, the Venetian blind was found
to exceed the visual discomfort threshold over a large fraction of the day during equinox conditions.
Notably, these peak periods of visual discomfort occurred during the best periods of daylighting
performance. Luminance uniformity was analyzed using calibrated high dynamic range luminance images.
Under clear sky conditions, the OLS was found to increase the luminance of the ceiling as well as produce
a more uniform distribution. Compared to conventional venetian blinds, the static optical sunlight
redirecting system studied has the potential to significantly reduce the annual electrical lighting energy
demand of a daylit space and improve the quality from the perspective of building occupants by
consistently transmitting useful daylight while eliminating window glare.