I have 2 lights in the room. one is a point light, that ligts up the room, and the other is a spot light that points towards the lava to make the lava brighter.
here is a short video showing the problem: https://i.gyazo.com/30d2118c3fbc6e2da91e02fdfa3c5d29.mp4
Sorry to necro post, i was looking for a solution to a slightly different problem. But, I think you just went about the lighting wrong. Your using a light that has to send a ray cast down, hit the ground, and generate light. Your player (hero) is the issue. When you stand under the light, even a small bit, the ray cast is hitting you. Better option: Use a self illuminating texture on the magma, or a point light closer to the magma, with a high intensity and low range. See this video for more options: https://www.youtube.com/watch?v=VnG2gOKV9dw
Hope this helps