Do not change the lighting. Change the surface properties instead. The key is [`Glow`](https://reference.wolfram.com/language/ref/Glow.html).

 PlotStyle -> Directive[Black, Glow[Red]]

[![enter image description here][1]][1]

We set the colour to black so no light is reflected (and the lighting has no effect on the rendered colour). Now whatever colour you put in `Glow[...]` will be used for rendering the entire object.

This is not only a simpler solution, it also allows mixing shaded and flat objects in the same scene.


 [1]: https://i.sstatic.net/Z388w.png