Changing the ambient and environment colors will effect how the lighting behaves. Change ambient from white to black and render the same scene and you should see a difference in color saturation, shadows, reflections etc. I think you use it for night scenes and stuff, but I haven't mastered it yet. Exposure control is also on the tab and is very helpful for getting stuff to look right. Effects are like fog and stuff and are cool, but tricky as well. Look at the help and it will explain those things. Then you just have to experiment.

The big questions is: are you using GI? If so, forget about ambient light and leave it alone. GI creates it's own ambient light, which is one of its best features and why things look warm and real.

If you are using scanline and want to get a good result, crank it down to 0 or close to it. It's 'fake' light and makes things look artificial.

Environment is the back ground and is what will be reflected in objects.
Different GI programs (Final Render, VRay, etc.) have different settings to include environment settings in the lighting solution. Generally speaking, it doesn not alter the lighting.

Effects are just that, effects (fire, lens flares, etc.). They don't actually cast light, so it's only visual.

Lighttracer is a primitive version of good GI. It's too slow to do much with, but the results are decent if you have time to just wait.

Thanks trace and hasselhoff - advice made a big difference.
Much appreciated.

d.