White noise with light source materials

[Vasily]

Maybe it's common thing but how to get rid of that white noise that appears when I use light source materials in my scene?

I tried to increase samples to 128 but it doesn't help.

[Speedster]

If in KeyShot 5, try changing the material to a plastic or advanced.  Noise is usually from roughness.  If in KeyShot 6 try Interior mode with Maximum time- the time has to be played with.
Bill G