The Rules of Light

For this tutorial, I will be teaching how to render light from imagination. We will be rendering a ball, but the rules of light can be applied to any form, be it a box or cylinder. It’s all the same.

Let’s talk now about the 2 different kinds of light and 2 different kinds of shadow.

There is direct light, which is the light that directly lights a form. Then there is ambient light which lights shadows. The way ambient light works is that light shoots out in a straight line, and then when it collides with a surface, it bounces*(usually towards a shadow). Ambient light is the reason why shadows are not fully black.

Moving on to the 2 kinds of shadows, there are form shadows, which are shadows formed by surfaces turning away from the light. Then there are cast shadows, which are shadows that are formed when a form occludes another form from light.

With that out of the way, we will now discuss how to render light from imagination.

First and foremost, we need to determine where the light source is, and the angle of that light source.

In this example below, the light source is the sun. In the sky and somewhat of a strong light source.

If we look at the example below, we’ll see lines pointing out of the planes of this sphere. Compare the angle of the light to the angle of the surface(the arrows pointing out of the planes) that light hits. If the angle is perpendicular you get a very light surface, possibly even a highlight if the surface is reflective enough. If the light is parallel, the surface is not iluminated. The terminator is when the light angle becomes parallel to the surface

What about the cast shadows? Well it’s actually quite easy. You can find the cast shadow by drawing an imaginary line from the terminator, in the direction of the light, and you keep drawing the line until it collides with another surface. repeat this process along the terminator so you create a shape. this shape is your cast shadow.

And there you go! You can apply these rules to any form, not just spheres. I would recommend also learning and practicing perspective, as it will help a lot as well for applying these rules.