What you say about blackbody being a red herring makes sense to me. What do you think of the argument at this link, regarding maximum concentration achievable

What you say about blackbody being a red herring makes sense to me. What do you think of the argument at this link, regarding maximum concentration achievable through optics? https://en.wikipedia.org/wiki/Etendue#Maximum_concentration https://en.wikipedia.org/wiki/Etendue#Maximum_concentration I get that that implies a maximum concentration factor of about 10,000, for a light source subtending an angle of 0.54 degrees (the moon's angular size from Earth, and also approximately the sun's.) Dylan16807 helped to prod me in this direction. https://news.ycombinator.com/item?id=18739190 https://news.ycombinator.com/item?id=18739190