Levels are greatest during the summer at midday. Factors that reduce the amount of PAR available to plants include anything that reduces sunlight, such as cloud cover, shading by trees, and buildings.
This PAR meter is a must-have tool for all growers. There is a proportional relationship between the band and the number of photons absorbed in the 400 to 700nm band and the rate of photosynthesis in plants, which is important for horticulture studies and monitoring plant physiology.