Lens Flare is an optical illusion produced by a camera. Hence the word "lens" in the label "Lens Flare".
As for sun glare it should be only a little bit bigger than the sun, for visualisation purposes- about half an inch around the AH sun but it shouldn't be circular. It should appear as large sharp and pointy objects coming away from the sun (like krypotinte I guess)...
Shouldn't block your whole view like when you are driving in your car- fighter pilots had much better aviation goggles to block out the sun than your average sun glasses.
-SW
