Yeah I couldn't see it on my phone either, but see it on the PC.
Though I wonder how much of an issue it would really be, I mean you have to look rather closely and if you play a game, you usually wouldn't...
The simplest way to make some "lighting" is just to use a texture, alpha blend it on an nearly black, slightly transparent full screen/window rectangle and render that to the scene.
That way you get a darker scene and where ever you applied the light texture it will be a lot brighter.