I have a simple scene with a sphere lit by a light. The light intesity and color are 1. The light placed directly behind my camera. If I use lamert model with diffuse color set to 0.18 I'm getting expected surface response - 0.18 in the middle of the sphere. However if I assign mantrasurface with diffuse color set to .18 and diffuse intensity 1, sphere gives incorrect response 0.36.

I was wondering if this is expected behaviour?