# Light Decay

## How to Add Light Decay in Maya

Lights in the real world decay as the light beam travels further from the source. If the light travels twice the distance from the source, the light's intensity is the inverse square or just 1/4 the original intensity.

For instance, if you were driving your car at night, an object that is 200 feet in front of the car would receive only 1/4 of the light for an object at 100 feet.

In Maya you can select between four different decay rates. They are No Decay, Linear, Quadratic and Cubic. Quadratic is similar to real world lighting.

Decay is only available with Area, Point and Spot lights.

#### Step One

Add a cube to the scene by choosing Create > Polygon Primitives > Cube. Be sure to include the options.

#### Step Two

Set the size to Width = 2.5, Height = 5 and Depth = 5. Press the Create button to add your cube.

#### Step Three

Select the Top view and duplicate your object two times by choosing Edit > Duplicate. Using the Move tool, move objects two and three so they stair-step in a negative z direction from the first shape.

#### Step Four

Add a point light to the scene by choosing Create > Lights > Point Light.

#### Step Five

Select the light and open the Channel Box. Set Translate X to 12, Translate Y to 4 and Translate Z to 22.

#### Step Six

With the light selected, open the Attribute Editor and set the Intensity to 1 and Decay to No Decay.

#### Step Seven

Click the IPR Render icon and marquee select in the render window to select the objects. As you make your changes in the Attribute Editor, they are updated in real time.

#### Step Eight

Notice that with the Decay set to No Decay, all the blocks are equally illuminated regardless of the distance from the light.

#### Step Nine

Change the Decay to Linear. You will need to increase the Intensity to light the shapes. With Linear decay the intensity decays in a Linear fashion. For instance, half the distance equals double the intensity.

#### Step Ten

Set the Decay to Quadratic. Once again the Intensity must be increased to illuminate the blocks. Quadratic is similar to the way that light works in the real world.

#### Step Eleven

The final Decay option is Cubic. Increase the Intensity so the light reaches the objects.

#### What Does Cubic Do?

Cubic is similar to Quadratic except the decay occurs at a faster rate.