macbook air Black Screen

Hi,

I have a macbook air (mid2010) on which the screen goes black randomly when using.

When typing an email or using pages the screen goes black for sometimes 2 seconds to sometimes 6 seconds.

If you wait then it returns to normal but is a real pain when you are typing and have to stop to wait for the screen to return.

I have updated to the latest release of Lion but this has not solved the issue.

Any ideas what I can do?

Cheers,

Kirk