Apple Shake 4 Tutorials - Manual (Page 140)

140 Tutorial 4 Working With Expressions
Creating Flicker on the Light
m In the Node View, select the RGrad1 node and insert a Color–Fade node between the
RGrad1 and Over2 nodes.
You can, of course, enable Autokey for the Fade1 value, then manually animate the fade
for a flicker effect on the light. You can automate this with an expression.
To insert a function into the value text field:
1 In the Fade1 parameters, click the value text field to select the current value.
2 Enter this simple expression: time
A plus sign (+) appears next to the value parameter. Click the plus sign (it changes to a
minus sign after you click it) to open the expression for editing.
The keyword time tells Shake to take the current frame number and use it for value.
Drag along the Time Bar to test it. As the playback slider moves to higher frames, the
fade value increases, too. This of course brightens the image too much, causing it to
blow out before you get to the end of the shot. Not exactly a great flicker effect.
You can put any expression into the value expression field. To create the flickering light
effect, you need to make small edit using the random function (rnd).