Now, these were done fairly quickly, so there is definitely room for improvement, and they can also cause effects that might be undesired - for example, a light texture in a flashing sector will always remain bright even if the sector has gone dark. However, they are a bit of fun to play around with so feel free to download them and do with them whatever you wish.
There are enough differences between Doom and Doom2 to justify 2 different brightmaps packs so here they are:
Doom
http://www.zen64060.zen.co.uk/examples/d1brightmaps.zip (215 kb)
Doom2
http://www.zen64060.zen.co.uk/examples/d2brightmaps.zip (246 kb)
Each zip contains a pk3 which is the brightmaps and, if you want to quickly check them out, there is also a WAD in each zip which is nothing more than a very simple level with all the affected textures/flats for that game.
They require GZdoom and for brightmaps to be enabled in the shaders menu.
Screenshots:
Spoiler: