Select the pen tool. Click "Effect" to bring up the "Effect" menu. Then click "Stroke" within the "Generate" panel.
Choose "All Masks" and "On Transparent" in the "Effects" panel. This will apply all effects to all layers.
Select the stroke size to be "10" on the "Effects" panel. This will give the burn the approximate size of a lightsaber strike.
Copy the stroke created in the previous step by pressing "Ctrl" and "C." Paste a copy of the original stroke on to the workspace by pressing "Ctrl" and "V." This will create a duplicate of the original stroke.
Click on the duplicate layer. Select size "3" in the size drop-down menu of the "Effects" panel. This stroke will act as the main part of the burn where the lightsaber touched the surface. The larger original stroke will be the spread of the burn from the lightsaber.
Align the smaller stroke so that it is centered on the larger stroke. Click the smaller stroke. Hold your mouse button down while moving your cursor to drag the smaller stroke to the center of the larger stroke.
Slide the transparency panel for the larger stroke to a lower number. There is no exact number. It's a matter of playing around with what is appealing to you. The larger stroke should be lighter and more transparent than the smaller stroke. Move your cursor around the color palette to adjust the color.