Attenuation

Image on right rendered with attenuation

In the real world, the intensity of light diminishes over distance. Objects far from the light source appear darker than objects near the source. This effect is known as attenuation.

In nature, light attenuates at an inverse square rate; that is, its intensity diminishes in proportion to the square of the distance from the light source. It is common for attenuation to be even greater when light is occluded by small particles in the atmosphere, especially when there are clouds or fog present.

By default, attenuation is not used by lights in 3ds max. Consequently, the distance of the light to the object is meaningless. Only the angle of the light to the surface has any effect unless you turn on attenuation.

You can manually control the rate of attenuation to omni lights and spotlights. You can also use attenuation with the Raytrace map. Typically, you should consider using attenuation for all of the lights in your scene and when you generate reflections and refraction with Raytrace, for two reasons:

For standard lights, 3ds max lets you explicitly set where attenuation begins and ends. This is partly so you don't have to worry about setting up strictly realistic distances between light objects and the objects they illuminate. More importantly, this feature lets you fine-tune the effect of attenuation. In outdoor scenes, attenuation can enhance the effect of distance. In an indoor setting, attenuation is useful for low-intensity light sources such as candles.