Well, almost... kind of. Stay with me 🙂
Watts is simply a measure of power 𝘪𝘯𝘱𝘶𝘵, what we're actually
interested in, is the 𝘰𝘶𝘵𝘱𝘶𝘵; INTENSITY and EFFICIENCY. Let’s dive in:
𝗣𝗔𝗥 - Photosynthetic Active Radiation: the “useful light” plants need. Anyone quoting lux/lumens…fahgettaboudit! 🤣
𝗣𝗣𝗙 (photosynthetic photon flux): the amount of PAR and quantified in umole/second.
Lights are put into an expensive sphere which records every photosynthetic photon pumped out. Divide the PPF by the input wattage, gives the 𝘗𝘖𝘞𝘌𝘙 efficiency. Or, divide by the cost of the fixture for 𝘊𝘖𝘚𝘛 efficiency.
However! Not every photon will hit our plant. To take an extreme example, imagine an led with all its diodes stuck on the top facing the ceiling, the PAR may be high, but that’s kinda shit, which brings me to...
𝗣𝗣𝗙𝗗, this is the INTENSITY; the measure of photons per second hitting our plant canopy, and expressed as umole/m2/sec.
A quantum meter (aka PAR meter) is used to measure and publish PPFD maps; the light is hung over an area measured at various heights. Companies may also just publish an average PPFD.
⚠️These maps are a good guide, but there's no standard in how PPFD is measured / published which makes it difficult to compare charts from company to company!
🤓 Current literature point to a sweet spot of between 600-900 PPFD in terms of maxing yield and maintaining a relative efficiency. In our graph, you'll see a diminishing return ie. rate of photosynthesis is not tripled by tripling the amount of PFFD, there is an upper ceiling. Whatsmore, PPFD of 1000+ will require CO2 supplementation
to be effective.
In summary, next time you visit your grow shop (hello!😉) ask about PAR output and look at all available PPFD maps, not just ones from the manufacturer!
FYI – we’ve the 👑 king of quantum meters landing (Apogee MQ500) so we can demo in-store, and have them available for purchase so you can optimise the hanging height of your light (rather than blast it full whack wasting energy your plants can’t absorb!)
As always, love to hear your thoughts, comments and experiences. Stay tuned 👍