I think you have to exaggerate certain things to get them over certain mediums.

The lens flare isn't telling you the sun literally makes polygonal shapes. It's telling you the sun is fucking bright and it's dazzling you, and it's doing that by reference to something we've seen in films shot with cameras.

You can achieve it other ways. HL2 Lost Coast - Valve's HDR tech demo - conveys the same basic fact by delaying the tonemap change. As you walk from the dark area to the bright area, the tonemap stays set for the dark area so your whole screen is washed out in white, until it gradually shifts to normal over about half a second. This is also how your pupils work, of course.