Step 5: Select The Brush Tool

Now that we've drawn our first path, the next step is to stroke it with a brush. For that, we'll need Photoshop's Brush Tool, so select it from the Tools palette, or simply press the letter B on your keyboard:

Step 6: Select The "40 Sampled Tip" Brush

Photoshop comes with several brushes that would work well for our light streak effect, but after trying a few of them out, I've found one I like the best. To select it, we'll need to bring up the Brushes palette. There's a few different ways to bring up the Brushes palette, and one of them is to click on the Brushes palette toggle icon in the Options Bar at the top of the screen:

When the Brushes palette appears, click on the words Brush Tip Shape in the top left corner of the palette. Then, in the Brush tip selection area on the right, scroll down near the bottom of the list and select the 40 Sampled Tip brush. It just says "40" in the preview area, but if you have Tool Tips enabled in Photoshop's Preferences, you'll see the words "Sampled Tip" appear when you hover your mouse over the brush:

Step 7: Lower The "Spacing" Amount To 1%

Down at the bottom of the Brushes palette, directly above the brush preview area, you'll see the Spacing option. Whenever you paint with a brush in Photoshop, even though it usually appears as though you're painting one continuous stroke, what Photoshop is really doing is "stamping" the image over and over again with the brush tip. If the "stamps" are close enough together, they appear as a continuous stroke. The Spacing option determines how far apart the stamps will appear, and by default, the option is set to 30% for our "40 Sampled Tip" brush. That's too much of a space for our effect. Use the slider bar to lower the Spacing amount all the way down to 1%. If you look at the brush preview area after lowering the Spacing amount to 1%, you'll see that the brush now appears as one continuous stroke:

Step 8: Set The Brush Size Control To "Pen Pressure"

If we were to stroke the path with our brush right now, the light streak effect wouldn't look very good because the brush would appear at the exact same size all along the path. We need the brush to taper off at both ends to create the illusion that the light streak is actually beginning at one end and ending at the other. For that, we'll need to tell Photoshop to simulate pen pressure for us, as if we were drawing with a pen tablet.

Click directly on the words Shape Dynamics on the left of the Brushes palette, directly below "Brush Tip Shape". Make sure you click directly on the words, not just in the checkbox to the left of the words. Clicking inside the checkbox will enable the Shape Dynamics options but won't allow us to change any of them. We need to click on the words themselves to get access to the options. Once you've clicked on the words, you'll see the Shape Dynamics options appear on the right of the palette. At the very top, you'll see the words "Size Jitter" with a slider bar, and directly below the slider bar is the Control option. This is where we get to decide how to control the size of our brush. We want Photoshop to simulate pen pressure, so select Pen Pressure from the Control drop-down menu:

Now, at the moment, all we've done is told Photoshop that we want to control the size of our brush according to pen pressure, but what if you don't actually have a pen tablet? If you don't have one connected to your computer, you'll see a little warning icon appear to the left of the word "Control" telling you that a pen tablet is required, but don't worry about it. In a moment, we're going to be telling Photoshop to simulate pen pressure for us, so for this effect, it makes no difference whether you have a pen tablet or not.

Step 9: Set Your Foreground Color To White

We have our brush ready to go. Now all we need to do is choose the color we want to paint with. We're going to want to paint with white, which means we need our Foreground color to be white. Press the letter D on your keyboard to make sure your Foreground and Background colors are reset to their defaults, with black as your Foreground color and white as your Background color. Then press the letter X to swap them, making white your Foreground color: