Now we have combined/”Merged” our layers, we are ready to apply effects to them both so that they seem like they were always the same picture. For a lighting effect go to Filter>Render>Lighting Effects Now we’ll get a menu asking us which light we want to use. The other options may be useful another time, but for right now we need “Spotlight” which should already be selected. Play around with the different options and see what they do, I edited the points of the shape to get the shape I want and then I used the Focus option to narrow down the light source.
Here’s the final image. As you can see the lighting has changed on both the background and the model. If you wish to do this to just a normal picture with a background you’re happy with – skip out the merging step!