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Q. I am an architectural 3D renderer trying to use real world light values in an interior rendering. I am using a rectangular light in a 4 x 4 window to mimic daylight coming through and want to know if there is a lumens/sf value (or range) that I can use for an unobstructed north facing window on a cloudless day at noon.

—C.L., Salt Lake City, UT, USA

A. I ran an AGi32 model of a 20' x 20' space in Salt Lake City, Utah with a clear (100% VT) north-facing window at noon on the summer solstice. The model predicts 1426 lumens/sf at the window surface. You can probably assume that these results are reduced linearly as the visible transmittance (VT) of the window is reduced. Hope that helps.

—Scott Schuetter, PE, LEED AP BD+C
Energy Center of Wisconsin

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Answers to your daylighting questions

Scott Schuetter, PE, LEED AP BD+C
Senior Energy Engineer

Tate Walker, AIA, LEED AP
Senior Energy Engineer

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