3D Lighting
The virtual lights used in computer-based, three-dimensional (3-D) images and films have a key advantage over real world lights: They can defy physical laws in order to produce dramatic effects. But virtual lights also suffer problems that real lights don't have--especially problems from the computer resources (e.g. memory, processing power) consumed by virtual lights for free 3d models. One point that both 3-D light artists and their audience can agree on is that 3-D lighting is becoming increasingly more true-to-life.
Types of Lights
One type of 3-D light is called a directional light. This light throws parallel beams, much like the sun's rays (which aren't actually parallel, but seem so from Earth's point of view). Shadows from directional lights are also parallel to each other, which gives the scene's audience a visual depth cue: They sense that the light source is far from the subjects being lighted. By contrast, the rays and shadows from spotlights are not parallel. You can thus sense the light's position in relation to what it's lighting. This can potentially make a scene more realistic because its viewers can sense elements of a world larger than the immediately visible scene.
Shadows.
Three-dimensional lighting uses two main schemes for creating shadows from light. One is called a depth map. Depth map shadows are the most commonly used shadows because they tend to be faster to compute and require less RAM (Random Access Memory) than ray-traced shadows.
Depth maps (or shadow maps) are stencils visible only to a scene's lights. Before a scene is rendered, a stencil is made for each light in the scene. The rendering software traces paths from the light to the scene's objects. Wherever an object blocks a light ray, the software adds to the light's stencil free 3d models.
When the renderer begins computing each pixel of the scene, it uses the stencil: Wherever it blocks light, the renderer doesn't do any calculations. Shadow maps can thus greatly reduce rendering time.
Ray-Traced Shadows
The other kind of shadow-maker is called a ray tracer. Ray tracing generally leads to more realistic shadows than shadow maps because it computes each ray of light that strikes a virtual camera's lens. Ray tracers work backwards, casting rays from the camera's position out to the scene's objects, and back finally to the scene's lights. The number of rays that needs to be computed could easily exceed the paths needed for shadow maps. Calculation thus typically takes longer for ray-traced shadows free 3d models.
Daylight Systems
One convenient feature of some 3-D software is that of daylight systems. These systems simulate the color, intensity, angle and other aspects of sunlight, given the location and time. For example, if you enter February 27, 1981, 12:23 p.m. and Marietta, Georgia, as input parameters for a daylight system, the software will re-create the lighting conditions (minus weather) that you'd see if you were in Marietta on that day. Such systems are useful for lighting scenes that require physical accuracy, but don't necessarily produce dramatic or interesting lighting.
Tunable Attenuation
The output of human-made lights fades with distance in a predictable way. But to create scenes that viewers like to look at, 3d lighting artists can choose to duplicate, ignore, or manipulate this phenomenon, which is called attenuation or simply light decay. For example, a character walking through a dark house carrying only a candle wouldn't be easily visible. But, changing attenuation parameters for the candle allows its light to reach and illuminate the character.
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