This is using a free HDR I found somewhere - don't remember where. The file is something about Reno Suburb. Anyway, the 10% sun reflection reads out as RGB 119, 120, 119. Do the math, (120 / 255) ^ 2.2 = .1905. So the sun's intensity is recorded in this image as 1.9. This is technically an HDR, but it's only 2x range, or one stop over, so blah.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)