How to do adaptive lighting for stable frame rate?

On certain Android devices even one pixel light is too much and our game falls under 30fps. What is a reliable way to detect bad frame rates? On some devices no lighting at all is useable. In that case I'd like to turn of lights all together. But then I would need to change all lit materials to unlit ones to maintain visual quality.

What is a practical way to do this? Are there other methods to degrade rendering quality to get a better frame rate?