Depending on the look you’re going for, you could try a number of techniques that don’t require real-time lights:
- Screen Space Ambient Occlusion (SSAO)
- Screen Space Curvature post process e.g. "Cavity" shader effect like Blender 2.8 viewport for Babylon.js?
- Baked lighting:
- Lightmaps
- Baked vertex colours e.g. https://www.youtube.com/watch?v=L8hC-Cp1tJ0
- Gradient textures e.g. https://www.youtube.com/watch?v=9ITJgW9hVrE
No doubt others will have more suggestions too.