This paper presents a photosynthetically active radiation (PAR) sensor based on an 18-band spectral sensor chipset with integrated optical filters. PAR sensors are an important tool for farmers and the proposed solution offers a path to low-cost PAR sensors. A technique for correcting the optical spectral leakage in the spectral sensor chipset is proposed and is applied to measurements collected indoors and outdoors. Tests results show that the proposed sensor and leakage-correction technique outperform lab-grade commercially-available PAR sensors.