WIGGLE

The Wiggle Expression 

 wiggle(10.100)

This Expression can be applied to almost any keyframeable attribute

to create a random type effect

An example of this would be to place it  on the position attribute of a layer.

This is how it is applied  option/alt Click on the  Position Stop Watch to enable the expression then type in wiggle(10.100) and hit enter on the number-pad.

When you play it back you will see your layer pulse randomly 10 times a second

 100 pixels from it's original value.

Now let's apply this effect to a lens Flare to create a strobe light effect.

but this time we will use a slider control to Wiggle the brightness of the flare

1. Create a solid, then go to effect - Generate - Lens Fare

Use the Default setting 

2. Create an adjustment layer and go to effect - Expression Controls -  Slider Control

3. Go to the Solid open the effect controls OPTION/ALT click the stop watch on flare Brightness.

This creates an expression 

4. Open the effect controls on the adjustment layer and open the slider control effect by clicking on the arrow next to the word slider control.

5. On the solid grab the pickwhip next to the flare brightness and drag it to the slider control, your flare has now gone black.

6. Select the Slider Control OPTION/ALT click the stopwatch and add a wiggle expression wiggle(10.100), now you have a blinking flare

7. Final Step On the solid OPTION/ALT click the flare center and ad a wiggle expression wiggle(2,10), this will offset the position of the flare making it a bit more random.

8. On the solid go to effect layer hue and saturation  then rotate the master saturation to adjust the color, then add a CC radial Fast Blur and that's it you have Disco Madness!