Ambient lights are used in modern games to fake the indirect illumination that exists in the real world. By adding a generally very weak light to the scene, we can avoid the 100% black shadows that really should not exist, all at a very low cost compared to proper indirect illumination or baked ambient light maps.

I have found that the simplest way to integrate these ambient lights into the Light Pre Pass system, and allow for other elements to change the lights throughout the game is to create a new light type that fits into the normal lighting model.

This is probably the simplest type out there, you just create a full screen quad and render it using a shader that writes the colour information directly to the light buffer. All we have to pass to the shader is the colour and intensity. (you could always pre-compute this, but beware of the byte->int32 auto promotion C# does)

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