VRayMeshLight vs. VRayEmissiveMtl

[rezvan23]

Hi.
What is the difference between VRayMeshLight and VRayEmissiveMtl?
I know some differences that mesh light is faster to render. and you can't blend mesh light with another material but with emissive material you can make blend material. I'm still wondering whats difference in calculation? is emissive material calculate in "building light cache"? which one is more accurate lighting?
(sorry for bad english, it's not my native language)

[konstantin_chaos]

Hi.
What is the difference between VRayMeshLight and VRayEmissiveMtl?
I know some differences that mesh light is faster to render. and you can't blend mesh light with another material but with emissive material you can make blend material. I'm still wondering whats difference in calculation? is emissive material calculate in "building light cache"? which one is more accurate lighting?
(sorry for bad english, it's not my native language)

Hi rezvan23,

The VRayMeshLight is an actual light source where as the VRayEmissiveMtl is a shader.
V-Ray will calculate those differently:
> The light source will emit direct light (calculated using shadow rays) and no GI is needed for the illumination to appear.
> The emissive shader will not emit any light. It relies on the GI engine to sample the surface and illuminate the surroundings. In this case the GI quality will strongly affect the resulting shadows.
If you do the simple test of rendering emissive material with GI disabled, you'll see that there is no light illuminating the ground plane or other surrounding objects.
Additionally the mesh light will give you more accurate lighting solution but will take slightly longer to render.
In simple cases you can just use emissive material.
On the other hand if you have complex shape that emmits really strong light and the shadows accuracy is important, the mesh light is the right choice.

Regards,
Konstantin

[rezvan23]

Hi rezvan23,

The VRayMeshLight is an actual light source where as the VRayEmissiveMtl is a shader.
V-Ray will calculate those differently:
> The light source will emit direct light (calculated using shadow rays) and no GI is needed for the illumination to appear.
> The emissive shader will not emit any light. It relies on the GI engine to sample the surface and illuminate the surroundings. In this case the GI quality will strongly affect the resulting shadows.
If you do the simple test of rendering emissive material with GI disabled, you'll see that there is no light illuminating the ground plane or other surrounding objects.
Additionally the mesh light will give you more accurate lighting solution but will take slightly longer to render.
In simple cases you can just use emissive material.
On the other hand if you have complex shape that emmits really strong light and the shadows accuracy is important, the mesh light is the right choice.

Regards,
Konstantin

Hi Konstantin,
Thanks for your reply. that's quite helpful