Lighting without reference

When I have to calculate lighting in a scene for which I cannot obtain reference, I use this handy trick. I had invented it quite a while ago, and I don’t know if anyone else uses it; at least I hadn’t found any references to it in the books I had read.

Lighting is, in principle, easy to create using formal perspective methods — on objects with straight lines. Organic or complex objects can’t be easily lit that way. Typically artists don’t bother and just use reference; but if your subject does not exist in nature, you are stuck. Some artists go as far as constructing and lighting scale models of the scene, but I generally cannot afford so much extra work! And since I do a lot of fantasy work, I end up using this trick often. It’s the next best thing to building and lighting custom models.

The trick is very simple in principle. Any object lit by direct light will have a lit part and an unlit (shadow) part, separated by the terminator. From the point of view of the light, the lit side is visible, the unlit side is invisible, and the terminator lies along the contour of the object. Therefore, if you draw the scene from the POV of the light, the contours in that drawing will be the position of the terminator (and by inference the falling shadow), and the surfaces parallel to the picture plane will be the highlights.

That’s it. A light-POV sketch makes the complex task ridiculously straightforward: just trace the terminator and the lit surfaces into your main drawing. Repeat for each light source. Render ambient occlusion, reflexes and the rest at your leisure.

Of course, pulling it off requires good spatial awareness and good understanding of solid form, perspective and (for living subjects) anatomy. The better you are at it, the truer your results will be.

This article consists mostly of pictures because it first appeared as a demo on conceptart.org forums; for the same reason it starts out with a sketch by someone else. But perhaps this is the best way to explain my lighting calculation method, because otherwise it would have been a wall of text.

So here are the files that demonstrate the method in use. For simplicity I did not take the light source’s distance falloff in account.