At the moment I have some ideas on how to increase or reduce brightness but which is better? To what extent is it controllable? What influences the brightness? The amount of light that can reflect your head. The smoother the surface, the better the light reflects. So I'm assuming that those ULTRA bright bald ones start out a lot when they shave (or they do not have any hair to shave) because when you shave a head and leave a little hair, it barely shines because it does not bounce so much light.