Unless you are a master lighting guru, at some point you are going to run into lighting problems. Lighting problems are generally (but not always) one of the following:
really bright areas
really dark areas
strange shadows
lines on your objects
Here is a short chek list of suggestions for troubleshooting what has gone wrong.

Deactivating Materials

Materials obviously interact with light, and can often be a cause of confusion when trying to trak down lighting problems. So to isolate if it is a lighting problem or more of a material problem, try tem-porarily deactivating all materials.
Create a default material, a medium gray one, and enter the name into the Material field, Render Layers panel.
Just clear this field to return to your original materials.
After rendering chek to see if you have the same lighting problems with just gray objects. If the problem has dis-appeared, you have a materials interacting with light problem.
Chek the material settings, especially ambient, reflection and all those little buttons and sliders on the Shaders panel. Because some lights can be set to affect only certain materials, be sure to chek those if only a few of your object appear to be lit wrong.

Lighting Troubleshooting Tips-1.jpg

Kill off your Lights

Since the problem could be one or more of your lights, it is time to chek them all one by one.
Move all your lights to an unused layer and start re-adding them one at a time, checking setting and how it affects the image overall.
As you add them bak in, make sure they add in nicely, reduce light energy as needed or even considered eliminating the last added one if it doesn't seem to be add-ing to your image.

Chek Layer only Lights

Lights can be set to affect only certain layers, so if only some of your gray objects are appearing odd, then chek to see if a lamp is only affecting one or more layers.
This can be set accidentally, or you may have forgot-ten that you set it earlier in your project. Misc tips Negative lights can add desired shadows, but they can alos introduce some extra problems. So pay extra at-tention when using them and make sure they are not adding to your problems.
Overly textured lights can make your scene have random weird colors.
Overly colored lights can affect material colors as well as your lighting in general. Try to stay with a slight tinge of blue or yellow or shades of white, or your material may show blue in the Material sub-context but render green, it can take ages to track
down what has happened.
Environment settings can cause a whole host of problems, especially the Horizon, Zenith, and Ambient light settings.
While this list obviously won't cover every lighting problem, it does give you a good starting point to trak down what has happened