Thunder Light

Open a file with following settings.

Step 2:

Fill the background with black color. Create a new layer and fill it with Black and white gradient. Name it Thunder.

Step 3:

Go to Filter in the menu bar _____ Render _____ Difference Clouds. Press Ctrl+I to Invert.

Difference Clouds                                                                   Invert

Step 4:

Press Ctrl+L to Apply following Level Settings and Ctrl+B for Color Balance settings.

Levels

Color Balance

Step 5:

Now we will animate our thunder light.

Go to Window in menu bar and click on Animation.

Step 6:

Change delay time to 0.1 sec.  Now click on "Duplicates selected frames" Icon and create 5 frame.

Step 7:

Now With Ctrl Select Frame1, 3 and 5, hide the "Thunder" Layer.

Step 8:

Select Frame 1 and Click "Tween animation frames" icon. Write 6 in "Frames to Add".

Step 9:

Now Select Frame 8 and apply tweening again, this time Frames to Add =2.

Here is the result