Jack Sparrow

Ok here is the problem.

I editted a bunch of clips, they are all on the timeline waiting to be converted to one large video.

The clips are sony hd files (avchd) with the extension .mts.

Nothing wrong yet. But here it comes:

In whatever format i render it so it will be one large video, it is always a LOT darker then the original. Shadows become full black areas, light areas look almost like they where filmed in the evening.

What profile do i need to set it to so it converts exactly like the original files?
I want to make sure the quality remains the same as the originals.

Is there some trick?! Known problem? Any help is much apreciated and google isnt my friend on this issue!

Thanks a lot!!