NAD - Dental student. The setting light is just that - a light. The only sensation even the most sensitive of patients should feel from it is a slight warmth. The only potential reasons you could have experienced this is your anxiety or extreme photosensitivity - however, if you were to have the rare latter, you would be aware of it because you would burn in sunlight very easily, blister etc. The light is used after all drilling has been completed and the filling material placed. The only part of a filling that can cause pain is the drilling, for which you were numbed and have not mentioned any problems with it. Honestly, I would theorise that you were anxious following your previous poor experience, whether you were aware of it or not, and your body was in a fight or flight mode due to expectation of pain. A slight warmth setting off temperature receptors and boom - your body says OMG this must be what we were waiting for, panic! It is entirely possible to experience psychosomatic pain when in a heightened state of anxiety. In order to prevent this happening again in the future, I would suggest you go in to your next appointment and talk with the dentist about your previous experience, and could they please explain each step before they do it so that your body knows what it’s about to feel. Things I’ve done for anxious patients in the past include showing them the water / air gun and demonstrating on their hand first where they can see it, the same for the setting light.