If you are using the physical camera, you need to also have the material pass that information to the camera. Its an easy one option switch; ‘Compensate camera exposure.’
Good values for the multiplier are around 1.5 to 2.0. Make sure that it’s not set at 0.0 accidentally.
If that still doesn’t help, you should then make sure you are also using your camera exposure … change the shutter speed, etc. Feel free to post a render of the full scene.
If you are just getting started with V-Ray, the support documentation is still incomplete. I know, because I am helping them with it. In the meantime, there are three excellent courses on V-Ray at lynda.com : (1) Fundamentals (2) Product Rendering and (3) Architectural. Full list and links are here.
If you are not a member, here’s a free 10-day trial.