So you're looking to have a dramatic light effect in your work and aren't sure how to go about it... In Photoshop there are always many ways to reach your goal, today we're going to focus on adding highlights by using the Color Dodge layer mode.
This is a fairly easy effect to produce realistic light hitting a surface. This method works best when you're working on mid/low range levels and with elements that don't have extreme contrast. It does very well when you have a shaded element and want strong highlights but might not work in other circumstances.
If you want to practice with this same tent, feel free to download this PSD (tree stock and original hilghlights layer included): Adding Highlights Turorial PSDBackground, layer and brush preparation
Adding highlights is something you usually want to do towards the end of the process. If you're going to add high contrast highlights