Adding lighter areas to the painting
Although I love using Layer blend modes to add light, I also like using Curves. Using a Curves adjustment layer, I can level everything up and brighten or overexpose the whole image. Now, I select the Curves layer’s mask, and Fill it with black so that the adjustment is hidden. Then I simply use a Soft brush to paint on the mask with white in the areas where I want to have some spots of light or light beams in the image.