The MQ-500 Quantum Meter from Apogee Instruments is a professional-grade tool designed for accurately measuring photosynthetically active radiation (PAR) across the full 400–700 nm spectrum, just like the DLI-500 Daily Light Integral and Photoperiod Meter and MQ-610 ePAR Meter. Built for serious growers, it precisely measures photosynthetic photon flux density (PPFD) in µmol m⁻² s⁻¹ from all light sources, including LEDs, HPS, metal halide, and natural sunlight. With calibration uncertainty within ±5% and long-term drift under 2% per year, the MQ-500 delivers reliable, stable measurements for greenhouses, growth chambers, farms, and aquariums.