Light Sources

This chapter will help you understand some specific types of light sources. There are many different sources of light in the world. Each has similarities and differences and must be handled appropriately in Light- Wave. Once you understand these specific light sources, you should be able to look at any light source and understand its properties. In the real world, a light source is defined as the direct source of illumination. The sun is a light source. So are a fluorescent tube, a lightbulb, a candle, and a tiki lamp. Described another way, physicists consider light sources to be events in which energy is spent, resulting in the emission of photons. Since this is not a physics manual, we will ignore that particular law. Apologies to physicists everywhere. For the purposes of this book and CG lighting in general, a light source is also defined as an indirect source of illumination such as diffuse or reflected light. The sky, for example, is considered a diffuse light source, although all of its light comes indirectly from the sun. Reflected light such as light from a mirror and diffuse reflected light, also known as radiosity, is considered a light source in the CG world. There is a good reason for this. Rather than create a physically accurate lighting environment in which diffuse light sources are actually diffused from the direct source, and in which reflected light is actually reflected 20, 30, or 100 (or infinite!) times, bouncing around the environment, we use cheats and tricks to create these effects. Why? There isn’t enough rendering time. Computers are not fast enough. Deadlines must be met. Rendering diffuse and reflecting light sources accurately is very CPU intensive and takes a great deal of time. So instead of actually diffusing the light from the sun by creating a physically accurate diffusion event the size of the earth’s atmosphere, we add a local diffuse light source that only affects the area within view of the camera. Instead of actually reflecting the light from the sun, we use no reflection but instead add a light source at the reflection point to simulate the effect. Usually the results are acceptable and save us hours per frame of rendering time.