I've seen and used domes/spheres to fake certain lighting effects. In particular "Global Illumination" and "HDRI":
Global Illumination (GI)
occurs when the light falling on any object in your scene is correctly calculated from the contribution of light from the other objects in the scene.
HDRI (high dynamic radioscity image)
refers to a particular form of image that has a much larger range of luminance information contained than a standard computer bitmap file. Typically, they are used as reflection or background maps from which lighting information is calculated beacuase they contain a huge amount of lighting information.
These are fairly advanced topics and ones I am just beginning to learn myself as you can see from the test images that I rendered this morning:
Link to rendering test images
The images are as follows:
Top Left: Maya Software renderer using default lights and no additional lights.
Top Right: The same scene rendered with a single white spotlight with a shadow setting of 512
Middle Left: I switched to Mental Ray, deleted the spotlight and rendered with default lighting.
Middle Right: Still in Mental Ray, but now with Final Gather turned on; 1000 rays, and min/max radius values of 0.1 and 1 respectively. Note the effect of global illumination - the green, red, and blue colors bleed into the surface plane.
Bottom: HDRI render using a hemisphere to contain the scene (not visible) onto which a lambert shader is applied. The lambert shader then has it's ambient color and color inputs mapped to the HDRI image and I have the doubled the luminosity of the color channel. The checkered plane has been replaced with a non-reflective white and the Final Gather values are 2000 rays, min-max radiuses of .8 and 8 respectively.
In terms of render times, the Maya Software renders took a few seconds, the Mental Ray default took about 15 seconds. Final Gather of 1000 rays bumps this up to about 35 seconds, and the HDRI render came in at a whopping 2 minutes (on a P4-1,5Ghz, 512kb RAM, HP laptop).
In case you're wondering - I was bored at work this morning!
That'll do donkey... that'll do...