arXiv2026
Cosmic-ray muons are among the most abundant high-energy particles reaching Earth's surface, with a flux of approximately one muon per square centimeter per minute at sea level, yet they remain entirely invisible to the naked eye, posing a persistent challenge for public engagement in particle physics. We present the Muon Bulb, a self-contained cosmic ray muon detector built within the enclosure of a standard commercial LED bulb, designed to produce a vivid and immediate visible light flash upon the passage of a cosmic-ray muon. The detector integrates a plastic scintillator tile coupled to a Silicon Photomultiplier (SiPM) for efficient detection of scintillation photons produced by ionizing muons. The SiPM signal is processed by a compact analog front-end comprising an amplifier and a leading-edge discriminator, which isolates genuine muon-induced pulses from background. Validated trigger signals are passed to an ESP32/RP2350 microcontroller, which drives an internal LED, causing the bulb to flash visibly in real time. The readout additionally enables wireless data transmission for real-time monitoring of muon event rates and flux measurements. The Muon Bulb is designed to serve as a high-impact outreach instrument across science museums, planetariums, K-12 classrooms and public science festivals without requiring specialized infrastructure. Its wireless capability enables networked classroom activities where multiple Muon Bulbs can be operated simultaneously, allowing students to collaboratively measure muon flux and engage in genuine data-driven scientific inquiry. The Muon Bulb transforms a commercial house hold item into a powerful tool for particle physics, making the invisible universe visible to everyone.