PAR
PAR is photosynthetic active radiation. PAR light is the wavelengths of light within the visible range of 400 to 700 nanometers (nm) which drive photosynthesis. PAR is a much used (and often misused) term related to horticulture lighting.
PPFD
An abbreviation for photosynthetic photon flux density, PPFD is a measure of the number of photons in the 400-700nm range of the visible light spectrum (photosynthetic active radiation or PAR) that fall on a square meter of target area per second. We typically use the max figure of 1000umol as the maximum PPFD we want to see from a light in a given area before needing to address other environment controls
DLI
Daily light integral describes the number of photosynthetically active photons that are delivered to a specific area over a Photo-period. This variable is particularly useful to describe the light environment of plants.
At this point I will highlight the fact that the above measurements in regards to strength or concentration is measured in μmol which refers to the actual photons of light as mentioned in the description of DLI. Micro-mole per joule usually written as umol/j or μmol/j. That means that for every joule of electrical energy (joule = watt * second) a certain number of photon micromoles are produced. Its these photons reacting in with the plant cells that provides the energy for plants to make ATP which is in turn used to bind carbon to sugar. So for every 2 photons of light we get 1 ATP formed but thats another thread
. Anyway these photons are the topic of our interest.So with that out the way its also valid for anyone following along but without hands on data of their lights to want a reasonable way of assume their lights potential for producing μmol. https://www.waveformlighting.com/hortic ... calculator is a reasonable source for a rough guide to more traditional lighting where actual data is unavailable
Now im sure your asking yourself well this data is all well and good but how can i use this in my own space???
Well actually there is already a good understanding that as a C3 dicot plant and likely having evolved in the field with up to 2000 PPFD from our very own sun that our lovely plant can and will enjoy DLI of up to and exceeding 50+ moles with all other cardinal principles in balance. Again as most of us dont have full control whats the average DLI we should look to aim for at each stage of growth?
As a general rule of thumb (to be adjusted to suit your own space)
The bottom threshold for optimal growth and photosynthesis is a DLI of DLI of 22
In late veg and through to mid/late flower a DLI of 40 mole can be achieved before the addition of CO2 is necessary
The Top threshold for optimal growth and photosynthesis is a DLI of 65 moles per day but this is with the addition of CO2
Alternatively a DLI of less than 20 mole and plants growth rate potential crawls around 30 - 55% which can be ideal for keeping mother plants, clones aswell as weak or sick plants
another great tool for quickly working out your DLI can be found here https://www.waveformlighting.com/hortic ... calculator
But for anyone who wants to do the maths for them self the equation is as follows
- μmol m-2s-1(the umol of your light fixture) x 3600 (the seconds in an hour) x Photoperiod ( (in hours) of light exposure per 24 hours)
Okay so now we have a good grasp of the amount of light we are looking to provide and how to understand the numbers we are working with, now the question is how can we alter these without affecting other factors in our grow space. A target DLI of 20-40 can be achieved in a variety of different combinations even when we maintain a minimum PPFD of 400 and a max of 1000. It actually give us a variety of lighting period options to achieve these measures but additionally we have the ability to adjust light height and for the sake of this point we will ignore running cost and simply the plant heath; a lower single point PPFD can be achieved but raising the lights making the less efficient due to the inverse square law but its can offer us the ability to dial in our DLI across a canopy potentially more evenly, decreasing light intensity but maintaining a more stable DLI
I hope this has given you some insight into how these numbers relate to your grow space and how you can use them to your advantage and if you have any thoughts or input please share
Discord
Links