At night in a dark room, the human body emits a barely perceptible glow. This light is so faint that only highly sensitive detectors can catch it. Some researchers thought this glow from the head could tell us about brain activity — no scanners or wires needed.
But when put to the test, the story changed. When the light from the head was measured under truly dark conditions, it turned out to be several times weaker than in earlier experiments. Those bright signals were just reflections of stray light leaking into the apparatus. The real glow from the head almost entirely originates in the skin, not deep inside.
So even if you capture a clean signal from the head, it tells you about the skin, not your thoughts. To search for the glow of the brain itself, you need different tools and more rigorous shielding from interference. For now, the 'light of reason' remains a beautiful metaphor, not a measurable quantity.
The human body does glow: the skin emits about 1000 photons per second per square centimeter — a thousand times weaker than what the eye can see.