
for darkness and contrast, try duplicating the layer, reducing the saturation of the duplicated layer to 0, and choose multiply from the blending menu.
Also, messing around the other blending possibilities can have pleasing results. Good luck.

Edit: I did some mucking around with it. A nice tool for differing the light is:
Make a white circle.
Cut the middle out of the circle.
Gaussian blur it a bit.
Soft light blending mode.
So it gives a kind of nice movable light.
( ,
Wed 1 Oct 2008, 14:46,
archived)
Also, messing around the other blending possibilities can have pleasing results. Good luck.

Edit: I did some mucking around with it. A nice tool for differing the light is:
Make a white circle.
Cut the middle out of the circle.
Gaussian blur it a bit.
Soft light blending mode.
So it gives a kind of nice movable light.