We all know light writing can be done by adjusting the shutter speed on a camera, but you can also do it in Photoshop as well. Now, it won't look like you took it with a camera, but I have a tutorial that will create a light writing effect in Photoshop. Now, to create a light writing effect, you will need to know how to use the pen tool. It took me awhile to figure it out, but once you do, it will be easier. In this guide, I will be using Photoshop CS3 to create a light writing effect to an image.
Step One: Open up an image you want to give a light writing effect. (File - Open)
Step Two: Create a new Layer (Layer - New Layer). Select the pen tool. Make sure on the top on Photoshop the box with the pen inside of it is selected.
Step Three: With the pen tool, create swirves from left to right (Refer to my picture to see what it should look like).
Step Four: Once you created your swirves, you'll want to adjust your brush. Set the brush color to white. Then change the brush size to how thick you want your beam to be. Smaller is usually better but you don't want it too small. Also, make sure it's a feathered brush, not hard edged. Click the image, A box will come up asking you something, click "okay".
Step Five: Without doing anything with the brush (making any marks), select the pen tool again. Right click on your line and select "Stroke Path". When the box comes up, make sure it's set to the brush tool. Select "okay".
Step Six: Once your path is stroked with the brush, right click again and select "Delete Path".
Step Seven: Once you have deleted the path, you will want to erase some of the lines to make it look like it's weaving in and out of the image (Refer back to my image to see what it should look like).
Step Eight: Next, we will add a filter that will make it look blurry but more realistic. (Filter - Blur - Gaussian Blur). Set the Radius between 2.0 - 5.5. It depends how fuzzy you want it to look.
Step Nine: Double click on the Light writing layer and a Layer Style Box should appear. Check the boxes Drop Shadow and Inner Shadow. There, you can adjust the color of the glow to what you would like. Make sure when you adjust them, you click their box so you only adjust those settings.
And that's all there is to it! The best thing I like about when doing this is when you're done and you use the brush, it looks like the light writing, that's how I made the extra dots around the light writing. This may take some time to perfect but overall it's a fun effect to add to photos!