how to make a circular light

This probably sounds really stupid but i tried all the lights and they either lit the intire terrain or the light made a weird hexagon. i just want a circle on the terrain to be lit. I tried forcing pixels and vortex but nothing changed. if you could help me with that that would be great!

P.S. heres another really stupid light question, what do light cookies do?

Someone already asked exactly the same question, but with a "STEVE" name: