Step 1

First open a new document at any size you like, but preferable more than 1000px wide and 1500px height or higher. Then fill up the background with Linear Gradient from top to bottom with light colors. Use any color you want. Then, by using the Ellipse Shape Tool, draw out some ellipses in the same layer . Well it looks like a group of cloud

Step 2

Duplicate the Shape Layer that created just now and hide the original layer (for backup purposes). Then, by selecting the duplicated Shape Layer which containing the clouds, right click the layer in Layers Palette and select “Rasterize Layer” to rasterize it. Immediate after this, apply Gaussian Blur on it with about 10px Radius.

Now we are entering the core step in this tutorial. After rasterizing and applying Gaussian Blur, now select the Rectangular Marquee Tool, and draw a selection at the most left part of the cloud. Then, hit Ctrl+T to turn the selection into Transform mode. You can drag the selection longer (press alt while dragging to get equal dragging on both top and bottom part) and hit Enter to complete the step. Now, marquee select the next part of the cloud and repeat the step until the end like picture below.

Step 3

The step above is to create multiple length of light stripes. For better result, you can marquee selects them with different sizes of width, for example, some fatter and some thinner. Besides dragging longer, you can also make them shorter too. You can also overlap the new selection with the previous one to create richer result. The picture below are the result of the select+drag step

Step 4

Well, the result does not look good at this moment. So, in the final step, select the layer and open up Motion Blur window (Filter > Blur > Motion Blur). In here you can smooth out the blurring effect even more, shown in the picture below. I’m using the maximum 250px Distance to achieve the smoother light stripes. Well this is the reason to use a bigger height of canvas so that the blurring effect won’t get cut by the canvas boundary.

Step 5

I add a gradient effect to get this effect.