Flickering lights can add atmosphere or draw a viewers attention to a specific object in an animation. Generating a flickering light in Adobe After Effects can be done by adjusting individual key frames; however, using the Wiggle expression is a much less time consuming method. The Wiggle expression generates random movement and only requires the input of two numbers, allowing you to fine tune your animation quickly and without having to adjust multiple key frames.
- Skill level:
- Moderately Easy
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Open the file containing the object you wish to add the flicker to. To create flickering lights, this should be a "light" object, however you can use the following approach to create random movement of any object. Select the object and alt-click the stopwatch by it to open "Expressions."
Click on the Expression line in the timeline. Type in "wiggle(x,y)" where x is the number of times per second you wish your light to flicker and y is the intensity. The higher the intensity, the wider the range of variation in the flicker.
Play your animation to view the flicker, then adjust the numbers in the wiggle expression until you have something you are happy with. Save the file.
Insert a null object to your animation by clicking "Layer | New Layer | Null Object." Rename the null object something like "wiggle control" so it is easily distinguishable from your other layers.
Add a slider control to the null object by clicking "Effects | Expression Control | Slider Control." Select the null object in the timeline and press "E" to reveal the slider control. Click the arrow to reveal the stopwatch on the slider control.
Highlight the first number in your wiggle expression -- the one that dictates how many wiggles there are per second. With the first number still highlighted, click and drag the pickwip tool to the stopwatch on the wiggle control layer. The pickwip is the tool that looks like a swirl on the expression position options for the wiggle. This makes the slider control the frequency of the wiggle.
Click the slider control stop watch to add a key frame. Move the keyframe to where you want the effect to start. Add a second keyframe to where you want the effect to stop. Set slider for both these keyframes to zero on the slider control. Add two more keyframes between the start and stop keyframes.
Increase the frequency of the wiggle on the middle two keyframes to the same value using the slider. When played through, the frequency of the wiggle increases for a few frames, holds at that frequency until the second keyframe, then decreases towards the stop keyframe. You can add more keyframes between the start and stop keyframes to vary the frequency of the wiggle expression more if you desire.
Play through your animation, making any adjustments as desired, then save the file.
Controlling the wiggle expression
Tips and warnings
- You can have the wiggle expression start and stop multiple times. Just add more keyframes later in the animation and adjust the slider controls.
- Keep a spare save of the original animation before you start playing with the wiggle expression in case you make a mistake and wish to go back to your original footage.
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