GoldenSkans, the lighting texture is the easiest one so far, if you are using photoshop (any version of photoshop, it doesn't matter) you just need to work with RGB channels, the blue channel is the light source layer, so every light source in the texture needs to have a blue tint. ¿how can you do that? well, by default in the original lightning texture file if you select ONLY the blue channel, the lights will be white, and the rest of the image will be black, yes, the lights are white and darkness is black. So if you want to edit the lightning texture select blue channel painting white the lights you want to create or fix, you can be creative and create any lights you want

but they must be coheret with main texture shapes. When you will finish editing the texture, bare in mind that everything than isn't a light source MUST NOT have any blue tint, check the blue channel and if ONLY the light sources are white and everything else is black then you're ok