Optimal Grow Light Size for Cannabis

Cherry X

Jun 30, 2021
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To determine the optimal grow light size, it is important to consider the optimal PPFD (density of light) for growing cannabis and how that Optimal PPFD converts to an Optimal PPF (amount of light).
The Optimal PPFD for Cannabis:
The data from Chandra et al. confirm that the optimal photon density for peak cannabis photosynthesis is between 500 and 700 µmol/m2 (PPFD). It also shows that we should avoid going over 1000 µmol/m2 (PPFD) which could lead to damage. With artificial lighting, the distribution of light is never perfect. Therefore, we want to ensure that all areas of the canopy get at least 500 µmol/m2 (PPFD) and that no spot receives more than 1000 µmol/m2 (PPFD). We recommend an average of 700 µmol/m2 (PPFD). With most grow lights, an average of 700 will ensure that you stay within the optimal range for peak photosynthesis in all regions of the canopy.
The Optimal PPF for Cannabis:
PPFD is a density measurement which is expressed as micromoles per square meter. To convert PPFD into a quantity measurement, we multiply it by the area in square meters. Since the optimal average photon density is 700 µmol/m2 (PPFD), the optimal number of photons is 700 µmol Usable PPF per square meter. This converts to 65 µmol Usable PPF per Square Foot. To calculate the total amount of light that you need for your grow space in Usable PPF, simply multiply the square footage by 65 (Sq. ft x 65 = µmol Usable PPF).
Usable PPF, Total PPF and “Calculated Values”
There are three ways that PPF values are measured or calculated. PPF values may be a “Calculated PPF”, or they may be measurements of “Total PPF” or “Usable PPF”. As we explain in our Grow Light Metrics Primer, there are significant differences between the different types of PPF data. To make accurate measurements and comparisons, it is important to understand what type of PPF values you are working with.

trillions of atoms

Dare to dream...
Aug 31, 2006
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This means nothing to the average grower. Literally this is like pulling a trig book out in 3rd grade math.

Every plant is different.

I have tons of posts discussing proper lighting and how to know if you are giving to much intensity/lumens and what to look for.

It’s really easy.

watch the plants- they tell you what they like/don’t and what they have/need.

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