measuring ppfd

PAR -- photosynthetic active radiation or something akin to that, lol.. the range of electromagnetic radiation that reacts with chlorophyl in the plants... PPF -- Photosynthetic photon flux -- umol/s of PAR radiation measured at a single location. This is photons per second of PAR light, if those words make more sense. PPFD -- this is how much PPF you average relative to 1m^2. This makes comparing DLI to varying sized gardens apples to apples. DLI is always teh same DLI as far as total number of photons applied to the canopy per day. "rate x tme per area" is what this represents. DLI is what matters. You calculate PPFD and then reference it with hours of operation on a Daily Light Integral table to see what DLI results. 35 dli is 35 dli. It will result in the same growth regardless of any common sense range of operating hours for grow lights, all other factors remaining the same -- for autos. vege, or flower, doesn't matter You measure PPF at several evenly distributed points accross entire canopy and the average gives you PPFD. PPFD is about light per second over an area, not just photons per second nor 1 point of measurement. A quantum meter is the only way to properly measure it. It costs around 500 USD. Apogee instruments, bugbee's company, sells one. There are phone apps that convert lux to PPF and probably mislabels it PPFD, unless it tells you to take many measurements and it averages it out for you. The drawback here is that due to things like varying CCT, the conversion of klux to PPF is not a one-size-fits all factor. The good news is that nowadays, most growlights are within 10-15% of each other in regard to that fancy curve you see showing the amplitude of various wavelenghts the light produces -- i.e. you usually see 2 spikes in the blue and red regions. So, those phone apps are at best +/- 10%. Knowing exact PPFD is not super important. You can guesstimate this from the spec sheet of the light and the size of your grow area (umol/s divided by area in meters-squared will give you a rough estimate of PPFD -- in reality this will be a bit lower, but with very similar hanging distnaces and other variables, it's stil very useful). So, you attempt to start in a 35-40 DLI range (*ambient co2 conditions) and no matter what instrument you used to measure PPFD and resulting DLI, you still have to observe and adjust to the plant's resulting growth. Your ambient co2 is different, your climate is different, therefore you maximum DLI you can give will be different from anyone else -- although very similar in most cases.. still requires trial and error. internode length is your guide... if the stem between two nodes grows too long, you need more light.. if that internode remains too short, you need less light. Simple as that. Quick guesstimate using spec sheet... If it is accurate.. umol/s value divided by your tent's area in meters-squared. This gives a quasi PPFD to reference on a DLI table. Shoot for 40 DLI, because you lose some to walls, even if 90% reflective, and some of it misses the plant, etc etc... But due to consistency in typical hanging distances, this works well across most grow lights. Since it is only meant to get you close to where it needs to be, no matter what you have to engage in some trial and error. If you can, choose hanging distance based on evenness of light across canopy (even a klux meter or those free phone apps are good enough for this -- simply compare proportinal intensity from center to edges). Then, use dimmer knob to adjust intensity as needed based on the resulting growth patterns. If your dimmer options aren't sufficient, hours of operations are 1:1 proportional and a viable option as long as you dont break any rules regarding photoperiods (vege vs bloom requirements of dark cycle length etc). The last option should be adjusting the height, because this should be otpimized for best coverage wall-to-wall without sacrificing overall PPFD. other caveat -- although more wasteful with electricity, more power and further away will give better light penetration (inverse square law applies to how light spreads out from the source, not my own extrapolation.. a mathematica certainty) End of chat AI, BWAHAHAHA... just kidding. some mope here thinks knowing technical details can only come from chat AI instead of actually learning something on your own. Everything i said here can be referenced and verified. No bro-science of bullshit extrapolations included.