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Lets start off by describing what PAR and Lumens are, PAR or photosynthetic active radiation is the amount of light the plants see to photosynthesizes. Lumens on the other hand is the light output that is visible to us the growers not the plant. When shopping for an LED Grow light you will find a lot of manufactures like to advertise the total Lumens, but does that actually matter?
Since PAR meters are extremely pricey we will have to look at the advertised PAR ratings the manufactures have posted. When measuring a lights PAR ratings we use PPFD (photosynthetic photon flux density) to get the exact amount of PAR that actually makes it to the plant. A very basic guideline for how much PPFD a plant needs is as follows;
- 200-400 is great for seedling, clones, and mother plants
- 400-600 is perfect for early to late veg cycle
- 600-1000 is great for flowering.
Now you can understand why your LED's need to at a distance when growing to meet the guidelines above.Â
Here is an example using a popular novice LED Light. ViparSpectra v600
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With the light height set to 24" from plant canopy, The PAR value in the dead center is 488 PPFD, What this tells us is at 24" the dead center of your canopy is getting perfect amounts of PPFD for the vegetation stage. The light will need to be lowered to achieve higher values when flowering. As you can see the measurement lowers as the light covers over a larger area. This is important information to look at when purchasing the right size LED for your grow space. In a 3x3 Space the most outside parts of the canopy won't be getting the required amount of light they need.
To much light?
It is possible to have to much light or PAR (over 1100) as it will cause what is know as the light saturation point, at this point you will see a decrease in photosynthesis and will have to start adding C02 to the space.Â
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Hopefully this quick post explained why PAR is important when choosing the right grow light.
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Posted : 18/01/2019 9:26 am
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