how to make this “lighting” effect?

[Steve Bentley]

The problem with traveling masks is its really hard to bend and turn them without affecting stuff that’s close along the way, especially when you change directions. Its also a lot of keyframes.
Instead, try either of these.
On a separate layer above your scene:
You can make a painted path that has a gradient from one end to the other (either in AE with the new gradients on shapes, or in photoshop with a brush that changes color over its stroke – so black at one end and white at the other gradating in between).
The use the compound blur effect and feed the gradient as the “blur” source and it will act like a mask that runs along the length of the path proportional to the Maximum Blur in the effect. Use this element as a mask to reveal a glowy element. Then use a second gradient with compound blur to follow behind and close it up (assuming you want that)

Or

Use the stroke effect to follow stroke the path and animate the start and end parameters of the effect to give you a moving hot spot in the middle of the stroke – blur and glow as needed. You can either do this on transparent so the background shows through or make it a second layer and use a transfer blend like “screen” or you can do both of these compositing techniques.

[Greg Gesch]

Have a try using the Vegas effect, should do it. (A little gotcha; Vegas needs 3 points on the path for it to work.)

[Esther Casas]

Thanks for the tip! I applied Vegas to a path and it works great, thank you! 🙂