Formula for the ambient light intensity of a scene? I understand that ambient light is light that occurs a result of light from a given source refecting off an infinite number of points in a scene, thereby illuminating all objects in the scene uniformly and explains why areas not directly illuminated by a light source in a scene aren't pitch black.

So I guess ambient light gives everything in the scene the same basic "brightness". But how does one determine this value? I presume the ambient light is proportional to the primary light source intensity (a floodlight in a bedroom will surely produce more ambient light than a lit match in the same room) and inversely proportional to the scene size (a lamp in a closet surely produces more ambient light than a lamp in a hall). Is there a formula that gives ambient light "brightness" as a function of scene volume, light source intensity, and any other variables please?

Please excuse my naivety, as I'm a noob to computer graphics, and only a hobbyist at that.
Using an 'ambient light' term in your lighting calculations is an approximation of the indirect light reflected around the scene. Usually it's up to the artist to choose an appropriate value. There isn't really a formula, because the indirect light is dependent on many factors:


Light intensity
Light shape
The BRDFs of the surfaces the light will bounce off of
Visibility to the light source (Think the back of a deep cave)
etc.


You could use some kind of formula to get an approximate value, based on these factors, but, in my opinion, it's simpler just to do it manually per scene. Or, you can remove it entirely, and use more sophisticated methods to calculate indirect lighting.