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When I open my blinds, there is light enough to read a book outside while the lamp is on inside.

So when I close my blinds, does the light that otherwise will escape, stay inside and thus being lighter inside?

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up vote 4 down vote accepted

Your question probably reflects your surprise that the observed change in illumination in the room when you close the blinds doesn't appear commensurate with the observed light leaking out. But a good illumination meter, or even your cell phone camera, will detect the overall brightness shift readily. Your eye is very cleverly designed to work over a range of illumination from starlight to high noon, and senses logarithms of intensity, not intensity. The change in log I is like delta I over I, and is smaller where I is big. Further, the eye and brain compensate for changes in general illumination.

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Yes, the light that would otherwise escape will mostly reflect off the blinds and light the inside more. Some will also be absorbed by the blinds and turned into heat, but the net effect will be an increase in light indoors.

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This depends strongly on the color of the blinds. – Colin K Nov 14 '11 at 16:37
They're white... – user1009013 Nov 15 '11 at 13:32

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