The following will help you optimize your scene's lights, as well as troubleshoot common problems.
Specular and diffuse light contribution — Each light can contribute to a material's ambient, specular, and diffuse components. If you want a light to affect only the specular of a material such as Blinn, Phong, or Strauss, select Specular Only from the light's property editor.
If a light doesn't have to calculate its effect on a component, it renders faster. By default, all lights affect both the diffuse and specular components.
Toggling area lights — You can toggle off all of a scene's area lights before rendering by typing ToggleAreaLights in the Scripting text box.
Keep in mind that this toggles off the area lights for the entire scene and not just the active render or active layer.
Being selective — If your scene requires area lights, but only on certain objects, make those area light selective so they don't need to calculate lighting on other objects.
To create a selective light, refer to Using Selective Lights.
What is your spotlight looking at? — From any viewport, you can select a spotlight view to "see" what your spotlight sees.
In addition, any changes you make to the spotlight's view or position are carried over to the light's position and angle.
