>>3360018Pretty sure its a by product of having a light source larger than a singular point. You can image lightwaves as ripples in a pond, but that isn't quite right. Ripples travel straight away from the impact point. Light will travel in any random direction away from its origin (until it is reflected or absorbed). Light originating at the top of the light source has the ability to "splay" out to the point where is is visually bellow the light source. The halo appears brighter because it technically is. It is able to be hit by light originating from any visible point on the light source.
The size of the halo would depend on the circumference of the light source and the distance from it. The further you are from it, the larger the halo. The larger the light source, the smaller the halo.
Pic related is a half assed attempt at drawing the above explanation.
All that said, I could be wrong. This is just me trying to remember some youtube video explanation a heard awhile back.
