Ok dont use an ambient light because they make things look flat (because they illuminate everything equally, even occluded objects so they suck)

You do need some bounced light in there, think how the light would bounce down from the ceiling onto the floor and the desk etc. It's gonna be a bit hard to do but I'm sure you can get it. The only thing I'd say is that in that room, were it real, the desk would be quite dark because there isnt a heck of a lot of light available.

If you want to do the light outside then use a directional light and lower the intensity (Not an ambient)

Alan