Photoshop - Three Point Lighting model & shadow emulation

In this tutorial we'll learn something about "Three-point-light" model, which is - according to Wikipedia - "a very common lighting technique, used in both still photography and in film". It is in fact, a classical, simple scheme to achieve a softer lighting over some scene. Using three different light sources, one can illuminate a subject (a person or some object) , and by controlling light, shading and shadows, can emulate 3D object aspect in 2D areas. The light scheme is used to model the scene, so the viewer can see the shapes, shadows, and how these objects relates to others. Further we'll call these three sources of light, as "key light" , "fill light" and "rim or back light".
Back to Wikipedia and here are the definitions:

The key light, as the name suggests, shines directly upon the subject and serves as its principal illuminator; more than anything else, the strength, color and angle of the key determines the shot's overall lighting design.

The fill light also shines on the subject, but from a side angle relative to the key. It balances the key by illuminating shaded surfaces, and lessening or eliminating chiaroscuro effects, such as the shadow cast by a person's nose upon the rest of the face. It is usually softer and less bright than the key light (up to half), and more to a flood. Not using a fill at all can result in stark contrasts (due to shadows) across the subject's surface, depending upon the key light's harshness. Sometimes, as in low-key lighting, this is a deliberate effect, but shots intended to look more natural and less stylistic require a fill.

The back light (a.k.a. the rim, hair or shoulder light') shines on the subject from behind, often (but not necessarily) to one side or the other. It gives the subject a rim of light, serving to separate the subject from the background and highlighting contours.

Basically, the key light models the objects, adding main shadow and visual details, fill light moderates shadows and reduces overall contrast, and the back light enhance edges, and separates the subject from background.

Usually this stuff is done easy, with some 3d software, like Maya, or 3DMax, but with some skill and patience, it can be done usind 2D lighting filter from Adobe Photoshop. This tutorial may be useful for 3D designers or photographers who wants to enhance their photos, digital matte painters, or just for Photoshop users wanting to test their skills.
Tutorial is organized in steps, each step will contain the description of actions taken, and the result you should get. All work was done in Adobe Photoshop CS2, and I assume that you have some basic knowledge of working with Photoshop.
Here is the starting point and final result:

So here are the steps:

Step 1. - beginning
Let's begin with a dark scene (a dark room) with two objects two oranges. So we'll have a black background layer, and two layers orange1 and orange2 as in image bellow:

Name working file, say main.psd, and make a copy of it, say duplicate.psd. You will need this copy later.

Step 2. - Setting environment light and shadows, then key light over objects
Assume that key light is somewhere upper left of scene. There are two things to set:

first set the environment, draw the floor flash light, and cast shadows from key light

set key illumination effect on objects

To do so, make a new layer (Shift+Ctrl+N) , name it "main spot", select Eliptical Marquee Tool (M), draw a circle, select Gradient Tool (G), with Radial Gradient option selected, set foreground color to white (#ffffff) and draw the gradient from the middle to exterior. You'll get something like this:

Then on this layer (main spot), do Edit->Transform->Distort, give it an eliptical form, move it under objects, set it's transparency to 45-50%. Now to build shadows, make two new layers (shadow1 & shadow2) and repeat the steps above, with the only difference that you have set the foreground color to black (#000000).
Arange shadows under objects and finish with environment settings. You'll have something like this:

Next we'll set the key illumination over the objects. Select (make active) layer "orange2". Go to menu and do
Filter->Render->Ligting effects. Remember that we already said that key light is on the upper left corner of scene. Set the parameters as follows:
Intensity: 36; Focus: -33; Gloss: 53; Material: 2; Exposure: 6; Ambience: 0; Set the light position relative to the object as in image below:

You may use dodge tool (Soft brush: 60-70, Range:Highlights, Exposure: 70-80%) in order to enhance the shiny reflection look on the objects. Select layer "orange1" and repet operations above, with proper light position corrections. Now both objects should have the proper upper left key illumination.

Step 3. - The fill light
As from definition the fill light shines from a side angle relative to key. To achieve this, open duplicate.psd file. The basic idea is to apply the fill light over the unchanged objects from duplicate file and then combine with the corresponding object from main .psd file. So, on "orange2" layer from duplicate.psd file do again
Filter->Render->Ligting effects. Remember that fill light will come from opposite of key light, but don't do it too simmetrical. Set the parameters as follows:
Intensity: 14; Focus: 47; Gloss: 0; Material: 69; Exposure: 0; Ambience: 8; Set the light position relative to the object (orange2), then repeat steps for orange1, making proper corrections for light position. You should have something like that:

Now just select layer "orange2", copy and paste over the "orange2" layer from main.psd file. Name this new layer "orange2_fill" set transparency at 40-45%, and with a soft brush eraser tool, just delete the area from layer that covers key light illumination zone. Repeat these steps for "orange1" object layer. Here is what you should have, the key + fill light illuminations combined:

Notice that separation shadows are smoother, and the detalies fron ex-shadowed zones are more visible.

Step 4. - The back (rim) light
The back light is obtained by placing a source of light behind the objects. Usual back light is a strong source of light, sometimes even stronger that the key light. Basically we'll add to the right edge of "orange2" object a thin stream of light, then emulate the light diffraction effect, and finally add a subtle touch of glow over the edge to enhance the realism of scene.
So make orange2 layer active, then Control-shift and click on layer thumb to select the big orange. Make a new layer (Layer->New->Layer or Shift+Ctrl+N) and name it "orange2_rim_front". Select foreground color to '#f9e7d7', bring the layer to front (Layer->Arrange->Bring to Front or Shitf+Ctrl+] ), then Free Transform or Ctrl-T and distort the layer on horizontal. Deselect if still selected, make active layer "orange2" again, then Control-shift and click on layer thumb to get object selected, then Select->Feather feather radius:6-7, make active "orange2_rim_front" layer and cut. Delete the unwanted left zones and you should have something like this:

Now duplicate this layer, name it "orange2_rim_back" and send it backwords ( Ctrl+[ ) under the "orange2" layer. Set the transparency level for "orange2_rim_front" layer to 60-70%. Then move "orange2_rim_back" under "orange2" layer until remains only a thin curved line. Set the transparency to 85-90%. And with a soft brush (color '#f9e7d7'), opacity: 15%, draw a thin glow around this line of light, like a halo reflection from behind. Repeat these steps for "orange1" layer.
Here is my result:

Now we could be pleased with our work until now, but to make scene a little bit spectacular we can add some fog, and see rays of light that illuminates the objects.

Step 5. - Add fog to reveal sources of light
Make a new layer (Layer->New->Layer or Shift+Ctrl+N) name if "fog" and bring it to front.
Do Filter->Render->Clouds, and again until you find a proper fog configuration. Set transparency to 30-40% or whatever value you feel it fits your scene. Delete areas that cover objects. Again make a new layer (above the "fog") name it light and with Poligonal Lasso Tool make a trapezoidal selection like a beam of light starting from the upper left corner of scene.
Select Gradient Tool (press G), select Reflected Gradient option , set selection feather:30-40px, (Select->Feather) set foreground color to #ffffff, and draw the gradient from upper left to objects, into selection. Name this layer "upper left light" and set it's the transparency as it fits with fog (for me 73%). And finally, duplicate background layer, and with a big soft brush (for me 300px) drop a spot of light behind big orange, and arange it properly. The foreground fog will do the effect.
And here is FINAL result:

Some last word considerations. This technique works only with simple objects. It's obvious that complex objects with lots of faces and complicated geometry can't be treated othervise but with some 3D software shadowing capabilites.

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