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I am trying to come up with a method for creating a realistic highlight that emulates a natural sun (overbright core with radial gradation to lower values to represent atmospheric haze), yet still controllable via a positionable node like a normal light.
Applying a cropped HDR sun bitmap or radial gradient ramp to the texture slot of a Vray plane light - This works as long as you don't have a reflection environment behind the light. The issue is there is no way to make the Vray plane light transparent around the edges so you get a dark square border where the outer edges of the plane occlude the sky environment behind it.
Using a plane primitive with a Vray light material applied - This allows you to map the opacity, thus avoiding the background occlusion problem you get with a Vray plane light, but the issue here is that the sampling is much less clean than with a Vray light. The intensity of the VrayLightMtl needs to be set extremely high to get the object to appear in the reflection and you get a lot of noise unless you crank up your DMC sampling. Also this only affects the reflection component and not specular, unlike an actual light.
What I've settled on for now is a stack of 3-4 Vray sphere lights, growing in size and dropping in strength...one behind the other. This appears to fake the look of a sun with the glow around it and help get rid of the perfect hard edges CG highlight you otherwise get. Not ideal, but with some simple rigging it should be easy enough to control by our lighters. I would still prefer to find a way to make using a HDR texture of an actual sun work without getting the border edges.
Applying a cropped HDR sun bitmap or radial gradient ramp to the texture slot of a Vray plane light - This works as long as you don't have a reflection environment behind the light. The issue is there is no way to make the Vray plane light transparent around the edges so you get a dark square border where the outer edges of the plane occlude the sky environment behind it.
Using a plane primitive with a Vray light material applied - This allows you to map the opacity, thus avoiding the background occlusion problem you get with a Vray plane light, but the issue here is that the sampling is much less clean than with a Vray light. The intensity of the VrayLightMtl needs to be set extremely high to get the object to appear in the reflection and you get a lot of noise unless you crank up your DMC sampling. Also this only affects the reflection component and not specular, unlike an actual light.
What I've settled on for now is a stack of 3-4 Vray sphere lights, growing in size and dropping in strength...one behind the other. This appears to fake the look of a sun with the glow around it and help get rid of the perfect hard edges CG highlight you otherwise get. Not ideal, but with some simple rigging it should be easy enough to control by our lighters. I would still prefer to find a way to make using a HDR texture of an actual sun work without getting the border edges.
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