Search found 2 matches

by BFGaloot
Wed Feb 10, 2016 6:10 pm UTC
Forum: What If?
Topic: What-If 0145: "Fire From Moonlight"
Replies: 157
Views: 75354

Re: What-If 0145: "Fire From Moonlight"

A lens that spreads out parallel light seems to violate conservation of étendue. For the input, area times angle is 0 since the angle is 0. But the output is not zero. The cosine bit that someone else pointed out is one answer. The other is that there is no such thing as perfectly parallel light. A...
by BFGaloot
Wed Jan 13, 2016 10:05 pm UTC
Forum: What If?
Topic: What-If 0141: "Sunbeam"
Replies: 81
Views: 44087

Re: What-If 0141: "Sunbeam"

Someone asked if we could physically do this with mirrors. The answer is "no", since etendue (or radiance or luminance or in non-qualitative terms as used by laser jocks, brightness) is a conserved quantity. These quantities have units of power per steradian, and since the sun emits over 4...

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