Working with 3D Lights
Most 3D packages offer the same types of light despite different naming and iconic representation. The important thing to remember when lighting in a 3D environment is that the lights you are using are simply an attempt to simulate lighting in the real world. Think about traditional lighting setups as you start to work in 3D. It will give you a solid foundation to work with and you'll be surprised how effective even a three-light setup can be. Next we'll discuss the most commonly used lights in 3D.
Directional lights (see Figure 7.9) are most often used to simulate sunlight and moonlight. Typically functioning as a key light in a scene, they provide controllable and predictable illumination. Due to the fact that the sun is so far away from the earth, by the time the light reaches us, the rays are essentially parallel to one another (see Figure 7.10). That is why you will also hear the term parallel light when referring to directional lights. The farther away the light source, the more parallel the rays become. Directional lights do not fall off with distance; the intensity is constant everywhere in the scene.
Figure 7.9 A typical representation of a 3D directional light.
Figure 7.10 By the time the sun's rays reach the earth, they are nearly parallel to one another.
Ambient light (see Figure 7.11) is light that is spread everywhere equally in all directions without dissipating with distance. Although no true ambient light exists in the real world, its general purpose in 3D is to simulate the bounced light that occurs all around us. Essentially, it serves as a fill light. Computers are powerful, but to calculate every ray of light as it bounces off every object and changes color, intensity, and direction results in dramatically increased render time. We are using ambient light to simulate the bounced light due to the computational burden of actually raytracing or using radiosity lighting. Use very low intensity ambient light to create a uniform diffuse light in your scene.
Figure 7.11 An ambient light.
One of the most commonly used lights in 3D is a spotlight (see Figure 7.12) because of the amount of control the artist has over its parameters and variety of effects. Spotlights are often the key light in a scene as well. Of course, in the most traditional sense, a spotlight is what we think of when we envision a stage with a single performer in a focused conical beam of light, and it works very well for that exact situation. But spotlights can provide lighting solutions for an endless amount of situations.
Figure 7.12 A spotlight.
Point or Omni Lights
Just like it sounds, a point light (see Figure 7.13) emits from a single point in all directions. Also referred to as a uniform light, it is ideal for lightbulbs, lamps, candles, and the like. Point lights are extremely flexible and do a great job of producing these types of lighting effects.
Figure 7.13 A point light.
You will find many additional types of lights in various 3D packages. Each is a variation of the core types discussed here. Each is designed to serve specific purposes. You will encounter lights such as area lights, volume lights, skylights, and sunlight systems. Play around with each of them and you'll quickly discover their individual purposes even though their functionality doesn't stray much from the light types discussed here.
Global illumination attempts to more accurately re-create real-world lighting by calculating the bounced light from all surfaces. In real life, light not only emits from light sources such as lamps, candles, or the sun, but also every object in the environment reflects and emits its own light, adding to the overall illumination of the scene. Raytracing was one of the first global illumination algorithms developed to emulate this type of lighting. Although raytracing can do a nice job of calculating bounced light and accurate shadows, it is extremely slow and lacks the softness and accuracy of other more recent solutions such as radiosity. Radiosity renderers also calculate global illumination by taking indirect light, surface properties, and specularity into account, creating a much more realistic scene. Figure 7.14 shows a room lit without and with a radiosity solution.
Figure 7.14 Top: A room lit without radiosity. Bottom: The same room with a radiosity solution.
In Chapter 4, "Advanced Texturing," we talked about the surface properties of materials, such as specularity and bump mapping. It's important to point out that the surface characteristics have a significant effect on lighting. Lighting can affect objects with varying surface properties in drastically different ways.
Although the term global illumination is somewhat generic, just remember that it is essentially an attempt at bouncing and reflecting light in a scene to better simulate real-world behavior. Also keep in mind that as light bounces off objects, it picks up the color of those objects and carries it through the rest of the scene. Using small, low intensity colored lights is a great way to simulate this principle.
Sometimes called attenuation, falloff limits the distance light will travel from its source. Falloff is commonly localized to affect only the surrounding objects, controlling where the light shines. Falloff can be applied to any type of light we discussed and is very advantageous, especially when it comes to lighting 3D objects. Having the ability to contain and control where your light travels and how it illuminates your scene gives you the precision you need as an artist. 3ds max has a great representation of falloff that shows you exactly where your light will be contained (see Figure 7.15).
Figure 7.15 Falloff (attenuation) visually represented in 3ds max.
When you choose to use falloff on your lights for vertex lighting purposes, you'll find that you'll need to compensate by increasing the intensity to maintain the original brightness. It's not uncommon to have to increase the intensity by 50% or more.