First we establish a primary lightsource. The left side of the face is detailed and cut with shadow tones, while the right side of the face will remain smooth and defined with highlights.

• Lets begin. We are going to start with a silhouette mainly to illustrate how each lighting source will affect the shading of the face, the second source being superimposed on the first. Let us begin with our primary lightsource. It is just normal light which carries no specific hue filter. Theres not much to this, the left side of the face is left in shadow and is detailed with shadow, while the right side of the face, being lit, is going to be detailed with highlights, and the general feel will be alot smoother. The ambient lighting effect is a bit too weak to really consider the effect to become apparent even on Cliff's blonde hair. Thus we have just flood filled it to be a single shade at this point.

Here is where we introduce our secondary light source. Note that its brilliance is not as great as the primary source, and the contrast between highlight and shadow tones are not as great on the left side of the face because the brilliance is not as significant. Note that there are areas of "absolute shadow" that remain hidden from both the light of the primary and secondary sources.

• The portrait on the right just took the previous step a bit further, and we went ahead and added a bit more detail to the right side of the face with another highlight color, and simultaneously on the left side, defined some darker areas with an outline tone. At this point the left side of the face is still blank from the absence of light.

Now consider another lightsource, not quite as strong as the primary source, but it should also detail some facial structure with highlights, and cast slight shadows of its own. Notice how the highlights created by the secondary lightsource are no where near as bright in terms of luminosity when compared to the right side of the face. Because the light source is not as strong, the contrast between highlight and shadow tones are not nearly as great as they would be on the right side of the face, being lit by the primary source.

Study the face in particular. The cheek bones and side jaw are highlighted, not as brilliantly as on the right side of the face, but is highlighted nonetheless. Also note a weak shadow remains in the middle of the jaw (where the gap between the mandible and the cranium exists), as this area is neither lit by the primary nor the secondary light source. You could consider these spots as "absolute shadow" areas, not being lit by any light source, and therefore are going to be the darkest part of your image.

Moving down to the shoulder, this secondary lightsource is only going to slightly highlight some of the individual muscle groups. Consider now the area under the jawline, namely the left side of the neck. Technically, the ambient lightsource would hit this area. However, because the secondary source of light is not nearly as brilliant as the primary source on the right, it only slightly offets the dark shadow cast by the primary source. Therefore it remains relatively dark.

At last we add another highlight tone and a shadow tone. Both, once again, have a relative low contrast.

• This last step will complete the subtle ambient lighting effect. Now we will use one more highlight shade for the left side of the face. Remember that the contrast between tones are alot smaller compared to the right side of the face, so this new highlight tone should be only slightly more luminous than the previous one. Also, we want to give this new highlight tone a bit more saturation to represent that it is a different lightsource from the primary, also because it adds hue variation in your image and makes it more interesting to lok at. With this shade we are just ever so slightly highlighting the cheek bone and jawline no the left side, and a bit on the shoulder and trap muscles. Notice that this gives off the same "gloss" effect as the sphere in the previous tutorial. Also note that if your contrast is too great, and you did not AA enough to smoothen out the transitions, your image is just going to look chunky and unsightly, and the "subtle ambience" certainly wont appear very subtle.

Also recognize that another shadow tone was used to darken those shadows cast both by the primary source AND the secondary source, or in other words, your areas of "absolute shadow". Once again, be careful not to make this tone contrast too much with the other tones or else it will stick out like a sore thumb.

This bottom portrait is to show what effect your ambient lighting might have if you wished for your subtle ambience to have a specific hue cast on the object of study, which in this case is Cliff. You would only find this significance of saturation from the ambient highlights if it were a close by fire or a neon light or something of that nature.

In any case, this concludes our tutorials on ambient and secondary light sources. Go practice, theres no way youre going to get it perfect the first time, but at least you'll be a bit more informed than i was when i first tried this effect.