Blender 3D: Noob to Pro/Understanding Blender Lights

Blender provides several different kinds of lights:
 * Point: Single point light source. Useful to provide very localized light. The shadows can be sharp, or you can set its size to something nonzero to make the shadows fuzzy. Can represent light sources within the scene; e.g. if there is a lightbulb or candle or something in the scene, position one of these within it to give the impression of light coming from that object.
 * Sun: A light with parallel rays that will illuminate the scene with an even light. Because the sun is (effectively) infinitely far away, the position of this lamp does not matter, only its direction. Good to use in brightly-lit outdoor scenes (i.e. a sunny day).
 * Spot: Spot lights produce light constrained to a cone-shaped beam, and have some special features. They are the only light source that can be made visible with the 'halo' option, to simulate light in a fog. They are also the only light source that can cast buffer shadows (see below).
 * Hemi: 180°-wide uniform, shadowless light source. Great for use as a fill light, or as a back light, or to represent light from the sky. Similar to Sun, its position does not matter, only its direction.
 * Area: These are similar to point lamps, except that they are rectangular. As a result they can cast accurate raytraced soft shadows, at the expense of additional render time.

There are two different kinds of shadows that lights may cast: buffered and ray-traced. The main difference is that buffered shadows are much quicker to calculate, but take more memory, and can be of lower quality without some fiddling. Also strand-rendered materials (as can be used for hair or fur) cannot cast ray shadows with the Blender Internal renderer, so you have to use buffer shadows for them so their shadows look realistic.

Only spot lamps can cast buffered shadows. Hemi lamps cannot cast shadows at all.

Light Settings
Blender’s lights offer many settings you can mess with to adjust their effect, such as:
 * Energy — the strength of the light.
 * Colour — real lights often have a colour, rather than being pure white. It is common in photography to talk about lights adding “warm” (reddish/yellowish) or “cool” (bluish) tints to a scene.
 * Falloff — real lights get weaker with distance according to the well-known inverse-square law. But Blender doesn’t force you to conform to reality: point and spot lamps also allow for other options, like inverse-linear or even a custom curve.
 * Distance — even with inverse-square falloff, the intensity of real lights never quite goes to zero at any distance, though it may become too low to measure. Blender’s distance specification allows you to limit the effect of the light to a finite maximum distance. This can be useful for having multiple lights illuminating different parts of a scene, while minimizing unwanted interactions between them—a headache that real photographers and lighting technicians cannot avoid!
 * Negative — instead of adding light to a scene, this light source can actually darken the scene. Again, not possible with real lights, but useful for certain kinds of effects. In live action black cards are sometimes used to reduce reflection on the subject by absorbing reflected light. This light could serve to provide a similar function.
 * This Layer Only — this light only illuminates objects on the same layer(s). Another useful way to minimize unwanted interactions between different lights.
 * Specular — uncheck this box to prevent this light illuminating specular parts of materials.
 * Diffuse — uncheck this box to prevent this light illuminating diffuse parts of materials.

Lighting Without Lamps
It is possible to light a scene without lamps, or with fewer lamps. In the World Context of the Properties Window, there are three options, for “Environment Lighting”, “Ambient Occlusion” and “Indirect Lighting”.

Environment Lighting adds a shadowless light that seems to come from all directions and fill all parts of the scene.

Ambient Occlusion (“AO” for short) is supposed to mimic the effect of shadows darkening corners and crevices of real-world objects (in theory this should naturally fall out of accurate lighting calculations, but it is easier to compute it separately); Blender also allows you to use AO to brighten parts of the scene outside those corners and crevices.

Indirect Lighting tries to mimic light bouncing off diffuse surfaces and illuminating other diffuse surfaces. It only works when the “Gather” option (next panel down) is set to “Approximate”.


 * Ambient Occlusion Video Tutorial: http://www.youtube.com/watch?v=rKUAemD7oo4