Skylight Basics

Skylights are nothing new in the 3D world. The technique have been discussed several years ago on several 3D or CG related newsgroups and mailing lists. However, it is only with recent release of renders from the Arnold GI renderer that the interest for skylights have been hyped. We have all witnessed several renders à la "Arnold".

Skylight approaches

Different 3D apps implements them in different ways but basically they are all built on the same principle. It is an extension of an area light technique that consisted of laying-out an array of lights on a plane. For skylights, the lights are laid-out on an hemisphere. This makes it a little more complex to setup and although it is possible to do it manually, it is generally better handled through an application that will generate the dome of lights. The application approach offers the advantage that the light positions can more easily be better distributed.

Hand crafted skylights

Trying to uniformly distribute the lights by hand is nearly impossible and will generally produce light domes that have spots where the number of lights are more concentrated. This break the scattered light effect which should be quite uniform. One common type of concentration that hand crafted light domes produce is a concentration of lights at the zenith. This happens when lights are positioned at latitude-longitude intersections of a lathed sphere model.

Random skylights

An easy way to get a uniform distribution of lights around an hemisphere is to generate random position on the hemisphere. This technique works fine when the number of lights is high. When the number of lights is low, the random positioning produces non-uniform distribution which can be noticeable on the rendered image.

Geodesic skylights

Another technique that will produce optimal non-random uniform distribution of lights even when the number of lights is very low is the geodesic distribution. Although geodesic domes have been invented by Walter Bauersfeld in 1922, they have been popularized by Buckminster Fuller in the 50's.

One of the most well known geodesic structure in North America is the Geosphere at the Epcot center in Orlando, Florida. Another one is the USA's pavillion at Montreal World Expo '67 in Montreal, Québec, Canada now called Biosphere.

A nice starting place to explore the world of geodesic domes is the Geodesic Domes web site by Kirby Urner.

Geodesic domes have a useful property for building light domes. The distances between any 2 lights on the sphere is almost the same all around the sphere resulting in a very uniform distribution of lights. For a more detailed discussions about the types of geodesic domes I use for skylights and introduction to geodesic dome types in general see my Geodesic Dome Types for Skylights page.

Follow through to see How to Setup a Skylight in a Choreography.