Create panel > Lights > Create light. > Attenuation Parameters rollout
Attenuation settings cause distant objects to be dimmer.
Attenuation is the effect of light diminishing over distance. In gmax, you can set attenuation values explicitly. The effects can vary from real-world lights, giving you more direct control over how lights fade in or fade out.
Attenuation is not visible in viewports.
Note: With no attenuation, an object can paradoxically appear to grow brighter as it moves away from the light source. This is because the angle of incidence more closely approaches 0 degrees for more of the object's faces.
Two sets of values control attenuation for objects. The Far attenuation value sets the distance at which the light drops off to zero. The Near attenuation value sets the distance at which the light "fades in." Both these controls are turned on and off by a toggle called Use.
When Use is set for far attenuation, the light at its source uses the value specified by its color and multiplier controls. It remains at this value from the source to the distance specified by Start, then its value drops off to zero at the distance specified by End.
Adding attenuation to a scene
When Use is set for Near attenuation, the light value remains at zero up to the distance specified by Start. From Start to the distance specified by End, its value increases. Beyond End, the light remains at the value specified by the color and multiplier controls, unless far attenuation is also active.
You can't set the Near and Far attenuation distances so they overlap.
The Decay controls are an additional way to make a light fade out.
Procedures
To use attenuation:
Set the Start and End values.
Turn on Use.
Attenuation is now in effect for this light when the scene is shaded or rendered.
To see the attenuation range in viewports:
Set Show for far or near attenuation.
You can preview the effect of attenuation in shaded viewports only if you turn this on as an option in viewport preferences.
Interface
Near Attenuation group
Start: Sets the distance at which the light begins to fade in.
End: Sets the distance at which the light reaches its full value.
Use: Enables near attenuation for the light.
Show: Displays the near attenuation range settings in viewports. For spotlights, attenuation ranges appear as lens-shaped sections of the cone. For directional lights, the ranges appear as circular sections of the cone. For omni lights and spot or directional lights with Overshoot turned on, the ranges appear as spheres. By default, Near Start is dark blue and Near End is light blue.
Far Attenuation group
Start: Sets the distance at which the light begins to fade out.
End: Sets the distance at which the light has faded to zero.
Use: Enables far attenuation for the light.
Show: Displays the far attenuation range settings in viewports. For spotlights, attenuation ranges appear as lens-shaped sections of the cone. For directional lights, the ranges appear as circular sections of the cone. For omni lights and spot or directional lights with Overshoot turned on, the ranges appear as spheres. By default, Far Start is light brown and Far End is dark brown.
Decay group
Decay is an additional way to make a light's intensity reduce over distance.
Type: Sets the type of decay to use. There are three types to choose from.
None: (The default.) Applies no decay. The light maintains full strength from its source to infinity, unless you turn on far attenuation.
Inverse: Applies inverse decay. The formula is luminance=R0/R, where R0 is the radial source of the light if no attenuation is used, or the Near End value of the light if Attenuation is used. R is the radial distance of the illuminated surface from R0.
Inverse Square: Applies inverse-square decay. The formula for this is (R0/R)2. This is actually the "real-world" decay of light, but you might find it too dim in the world of computer graphics.
Tip: If Inverse Square decay makes the scene too dim, try increasing the light's Multiplier value.
The point at which decay begins depends on whether or not you use attenuation.
With no attenuation, decay begins at the source of the light.
With near attenuation, the decay begins at the Near End position. Decay overrides far attenuation.
Once the beginning point is established, the decay follows its formula to infinity, or until the light itself is cut off by the Far End distance. In other words, the distance between Near End and Far End does not scale, or otherwise affect, the apparent ramp of decaying light.
Tip: Because decay continues to calculate dimmer and dimmer values as the distance of the light throw increases, it's a good idea to attenuate at least the end of the light to eliminate unnecessary calculations.