PPFD stands for photosynthetic photon flux density and it measures the amount of photosynthetically active radiation (PAR) that reaches a specific area per second. PAR is the range of wavelengths of light that plants can use for photosynthesis, and it falls within the 400-700 nanometer range of the electromagnetic spectrum. Accurately measuring PPFD is crucial for ensuring that plants receive the optimal amount of light for their specific needs. Too little light can result in slow or stunted growth, while too much can cause plants to become stressed or even die. The PPFD level can also affect the rate at which plants produce flowers and fruit.