Most of the areas that are not light sources are gone, but we still need to manually erase the areas that are not light sources. Select the brush tool and set the foreground color to black. Then, paint over all the areas that are not light sources. This is what the image used in this tutorial looks like now:
http://photoshoptutorials.ws/images/stories/Photoshop%20Tutorials/Photo%20Effects/Star%20Filter/after-erase.jpg
Duplicate the layer and change the blending mode to screen. This layer will be used to create the first half of the star.

Open the Filter> Blur menu and select Motion Blur. In the Motion Blur window, change the angle to 45ยบ and adjust the distance to your preference of how large you would like the star to be.

The motion blur is barely visible and the ends are quite square. First, we'll make the ends sharper by applying the Motion Blur filter again. To do this, simply press Ctrl+F or open the Filter menu and select the first listing: Motion Blur. Now we'll make this layer more visible by applying an Auto Levels. Press Shift+Ctrl+L or open the Image> Adjustments menu and select Auto Levels. Once you apply Auto Levels, the flare from the first half of the star should be very visible.
