For the most part, lighting in the “real world” tends to just happen. The sun rises, we flick a switch, or we open the blinds and voilà: light. We might put some thought into where we place a lamp, how we angle the blinds, or where we aim the flashlight, but ninety percent of the time our experience with light is fairly passive. Things are different in the computer graphics industry.
Lighting Is Everything
As any great photographer would tell you, lighting is everything. OK, everything may be a bit hyperbolic, but having a well-implemented lighting solution can very well make or break a render. Without great lighting, even a fantastic 3D model can end up looking flat and unconvincing in the final image. We won’t spend too much time barraging you with reasons why lighting is such an essential (and under-appreciated) aspect of the CG pipeline. But make the page jump, and we’ll begin our discussion of 3D lighting techniques with an overview of the six types of lights found in common 3D software packages.
Finding the Right Lighting Solution
Even though it’s pretty easy to click the “create light," button in your 3D software package and place a light source in your scene, the reality of the craft is far more complex. There are a number of well established 3D lighting paradigms, and the type of scene usually determines which one is most appropriate. For example, techniques that work well for an interior environment usually make very little sense for an exterior shot. Similarly, “studio” lighting for product or character rendering requires a very different procedure from lighting for animation and film. In the end, every situation is different, but certain light types work well for certain scenes.
Standard Lighting Options
Point/Omni Light — A point light casts illumination outward in every direction from a single, infinitely small point in 3D space. Point lights are useful for simulating any omnidirectional light source: Light-bulbs, candles, Christmas tree lights, etc. Directional Light — Unlike point lights, which occupy a specific location in the 3D scene, a directional light is meant to represent an extremely distant light source (like the sun or moon). Rays cast from directional lights run parallel in a single direction from every point in the sky and are typically used to simulate direct sunlight. Because a directional light represents a distant light source, its x,y,z coordinate means nothing — only its rotational attribute has any bearing on how the scene will be illuminated. Spotlight — Spotlights in 3D applications are fairly self-explanatory due to the fact that they’re rather similar to their real-world counterparts. A spotlight emits a cone-shaped light field from a single point in space. Spotlights are often used for three-point studio lighting, and also for simulating any light fixture where there is a distinct visual falloff from light to dark — streetlights, desk lamps, overhead cone lighting, etc. Area Light — An area light is a physically based light that casts directional rays from within a set boundary. Area lights have a specific shape (either rectangular or circular) and size, making them very useful for simulating fluorescent light fixtures, back-lit panels, and other similar lighting features. Area lights can be used as photon emitters when using global illumination in Mental Ray, which makes them a popular choice in product lighting and architectural visualization. Although area lights do have an overall directionality, they do not emit parallel rays like a directional light would. Volume Light — The volumetric light is perhaps the toughest to wrap one’s head around. With default settings, it’s almost identical to a point light, emitting omnidirectional rays from a central point. However, unlike a point light, a volumetric light has a specific shape and size, both of which affect its falloff pattern. A volumetric light can be set in the shape of any geometric primitive (cube, sphere, cylinder, etc.), and its light will only illuminate surfaces within that volume. Ambient Light — An ambient light casts soft light rays in every direction, and can be used to elevate the overall level of diffuse illumination in a scene. It has no specific directionality, and therefore casts no ground shadow, however it is not truly omnidirectional like a point light. Ambient light is relatively similar to the light experienced at dusk, just after the sun has set.
Scenes Often Include Multiple Lights
The light types we’ve discussed here can be used for anything from simple three-point studio lighting to complex animated scenes that require 40+ lights. They’re almost always used in conjunction with one another — it’s very rare that a scene will only include point lights, or only include area lights, etc. Nevertheless, we’ve only just begun to scratch the surface of a deep and varied topic of 3D lighting.
