to paint with light in post-production:
1. apply the mid contrast with duplicate overlay, blending to let shadows through.
2. apply curves with mask for fill light.50% opacity
3. for key light, adjustment layer-saturation at 0 set to color dodge.(acts like a fresnel) 20% opacity
4. finally, bring back color modeling with levels-white output set to color. opacity 20%
if you do these steps in this exact order, you will have very natural looking lighting. most people don’t do these steps and simply raise gamma, making everything look unnatural.