What are the best LED grow lights? - LUMENS AND PAR (4/5)
LUMENS AND PAR
LUMENS ARE FOR HUMANS
You may have seen LED grow light information listed in Lumens and PAR. Lumens do not matter - at least not to a plant. Lumens are a measure of the amount of visible light emitted from a source. Chlorophyll mostly absorbs light in the blue range, red range, and far ranges of the visible spectrum. Chlorophyll does not absorb green or yellow wavelengths (although evidence suggests that green light helps drive photosynthesis). In sum, lumens do not tell us how well plants will respond to visible light.
PAR SETS THE BAR
PAR, or photosynthetically active radiation, is a measure of photosynthetic light energy (400nm-700nm range) that falls on the plant each second. PAR does matter. It is important for plant growth, yet, many cheap PAR meters read the entire PAR range and not just the wavelengths required for photosynthesis.
A spectroradiometer is the best tool used to measure PAR, especially for when comparing LED grow lights to fluorescent, HPS, or MH systems. A spectroradiometer measures the energy at each specific wavelength.
It is best to ask the manufacturer how they obtained their PAR readings. When you know the readings for a grow light you are able to place it at the correct heights for optimal PAR coverage.