graphics3d - What is the default Lighting in 3D graphics?

The default value of Lighting in 3D graphics typically uses "Standard", with several coloured lights, or "Neutral", depending on the type of plot.

What is the explicit lighting specification for "Standard" and "Neutral", in terms of actual light positions, directions, colours and types?

Answer

The answer can be found here: Change The Lighting Of Plots in the official How Tos.

For "Standard"/Automatic:

Graphics3D[Sphere[], 
           Lighting -> {{"Ambient", RGBColor[0.4, 0.2, 0.2]},
                        {"Directional", RGBColor[0, 0.18, 0.5], ImageScaled[{2, 0, 2}]},

                        {"Directional", RGBColor[0.18, 0.5, 0.18], ImageScaled[{2, 2, 3}]},
                        {"Directional", RGBColor[0.5, 0.18, 0], ImageScaled[{0, 2, 2}]},
                        {"Directional", RGBColor[0, 0, 0.18], ImageScaled[{0, 0, 2}]}}]

For "Classic":

Graphics3D[Sphere[], 
           Lighting -> {{"Ambient", RGBColor[0.312, 0.188, 0.4]},
                        {"Directional", RGBColor[0.8, 0., 0.], ImageScaled[{2, 0, 2}]},
                        {"Directional", RGBColor[0., 0.8, 0.], ImageScaled[{2, 2, 2}]},
                        {"Directional", RGBColor[0., 0., 0.8], ImageScaled[{0, 2, 2}]}}]

For "Neutral":

Graphics3D[Sphere[], 
           Lighting -> {{"Ambient", RGBColor[0.35, 0.35, 0.35]},
                        {"Directional", RGBColor[0.37, 0.37, 0.37], ImageScaled[{2, 0, 2}]},
                        {"Directional", RGBColor[0.37, 0.37, 0.37], ImageScaled[{2, 2, 2}]},
                        {"Directional", RGBColor[0.37, 0.37, 0.37], ImageScaled[{0, 2, 2}]}}]