How can I increase the darkness of shadows without increasing the strength of the lamp? I want to create a shallow and dim lighting effect around my scene, but I also want the shadows to be slightly darker. Unfortunately the only method I have found to make shadows sharper and darker is to increase the strength of the lamp, which creates an extremely bright scene.

Is there any way to make shadows artificially darker?
Perhaps it's possible using the Shadow output of the Lightpath node but I couldn't do it. 
What I could do, is enable the Shadow pass tick box in the Render Layers panel and then use that shadow pass to darken the shadows of the render with a mix(darken) node. Use a very small factor though as darken can be very intense.
Hope this helps you.