How big should a lens be to focus enough light to reach 1000 Celcius?

[Panthera Leo]

How big should a lens be to focus enough light to reach 1000 celsius?

I was wondering how big should a glass lens be to focus enough light to produce a temperature of about 1000 celsius at its foci?

What if the lens was made up of sth with higher refractive index, doesn't this reduce the size of lens?

A rough guess will do... I am just curious

Thanks in advance :)

 

[CJames]

Take a look at this thread:

https://www.physicsforums.com/showthread.php?t=315719

Also have a look into fresnel lenses:

http://en.wikipedia.org/wiki/Fresnel_lens

 

[HallsofIvy]

So we have yet another post (three or four of then today) that seems to assume that a specific amount of energy translates to a specific temperature. That is NOT true.