KPovModeler 0.2

Written by Olivier Saraja (olivier_at_linuxgraphic.org)
English version

Case 1: The point light

The point light is the default light, and also the simplest light available. It produce light radiating from a single point source, suitable to light sources such as candles, torches, bulb lights and so on. Usually, it gives the best result in closed indoors environment, and is quite inapropriate in outdoors environment where it seems very unrealistic, unless coupled to the Area Light option (see below). In most cases, if you set many lights in your scene, you will experiment a light over-exposure.

There are two means to solve this. The first one is useful to lights with neutral colors: if you set all the three color components to the same value, the value then specifies the light intensity: low values like 0.15 or 0.30 will give darker lights than higher values like 0.80 or 1.0. Of course, you can also set the three components to a value greater than 1.0 to obtain over-exposed pictures with a single light sytem.... The second mean is to use the Fading properties, which need more explanations.

In fact, the Fading property lets you deal with the intensity of the light system: Fade distance and Fade power are discussed below.

Fade distance: it indicates at which distance from the emitting source the system start to loose intensity. Hereafter are example renders for increasing Fade distances . It's very easy to see the influence of the fade distance on the lighting of the whole scene. The greater the value, the more the scene is lit. Of course, if Fade distance is kept unchecked, the light intensity is constant throughout the whole scene, lighting it up to infinity if the lamp is set high enough in the « sky ».

In this example file, you should note that the Fade distance is calculated from the emitting light system, not the center of the scene. Even if it seems obvious, it explains why, with a Fade distance equal to 1, even the red sphere is in pitch dark shadows on the first picture. When activating the Fade distance option, you certainly will have to experiment with the settings until you achieve the proper illumination intensity. This option is particularly important in scenes involving more than one light source, because the energy of each will add to each other, resulting in an over-exposed rendering, as already discussed before.

Fade power: this parameter illustrates how "quickly" the light becomes dull once the Fade distance is achieved. Please note that Fade power must be greater than or equal to 1. For high Fade power values, you can get results close to the spot light effect, as shown on the following pictures made with a Fade distance set to 10. The higher the fade power is set, the sharper is the frontier between light and darkness.