How to determine proper light level using a Quantum meter?

Discussion in 'Lighting' started by kjones6160, Jul 11, 2017.

  1. Hello folks! I'm new to the grow scene and have started my first grow from seeds. My setup consists of two White Widow Auto plants using DWC bubble buckets with rockwool starter cubes and hydroton in 6 inch net pots in a 2'x4'x7' Gorilla tent and Advanced Platinum P600 LED light with a Hydrofarms LGBQM QuantumPAR meter. I'm trying to determine if I should just set the lighting distance from the top of the week old seedlings based up measured distance base on manufacturer specs or actual micromoles per square meter readings? It seems that actual PAR measurements with a Quantum meter would trump any physical distance placement of the lamp from the plants. My 5 day old seedlings are currently getting about 325 umoles at their leaves using the VEG only setting on the light. I don't want to burn the little ladies by moving the light too close but I'm not sure of what the optimal umoles/m2 level should be for the different stages of growth: seedlings, veg or flowering. Any advice on how many umoles I should shoot for at each growth stage? I've set up the tent on a 18/6 light cycle.
  2. You are WAY overthinking this... just hang the light like 20" away from the seedling and be done with it.
    • Disagree Disagree x 1
  3. Thanks. I have a technical background and my analytic mindset automatically kicks in with everything that I do. I'm probably being somewhat anal about it but I want to shoot for the best yield possible given my initial equipment investment in my new hobby :)
  4. I can respect that. I've never heard of anyone going about it the way you are trying to but i can say that it is very likely they are getting more than enough light at this point. You really wanna focus on optimizing your lighting situation when it comes time to flower.
    • Friendly Friendly x 1
  5. Dude you are 100% correct in your thinking, if you have the proper tools (which you do) then use them. umoles trumps everything. Rollitup has a big thread on this just recently, spectrometers, par meters etc.
    As I do not have a PAR meter I cannot tell you exactly what is going on with my canopy, but you can.
    Best case scenario in flower is 900-1000 um. 300-600 through various stages of veg I would suppose.

    For everyone else, there is a sort of backwards method to find umoles, but I wouldn't take it as gospel. I dont know, maybe the math is correct maybe not, would take someone with a par meter to find out.

    From Lumens.
    (Total lumens / total watts)/325= PAR Watts
    Here it gets sticky, you need to know the specs for the Diodes in your light, specifically the umoles/joule rating.
    If you dont know this data, stop here. If you do...
    PAR Watts * umols/j = PPF (photosynthetic photon flux)
    To get PPFD convert your square feet to meters then
    PPF / Sq M = PPFD and is a measure of umoles/m2/second

    a decent article of these measures for everyone else confused by these measures
    • Like Like x 1
  6. Nice, may get some more use out of my Seconic 608 cine light meter, I have it around here somewhere!

    Sent from my XT1650 using Tapatalk
  7. I have one of those cheapo Lux meters and my smartphone has an app as well. My phone is definitely more accurate, but either is good enough to sort out hotspots and to get a general idea of what your plants like. I have yet to buy a par meter, but if I do get one it will likely be the one the OP has as its inexpensive. But from what I hear from the pros on these boards, the Apogee is the way to go.
    SQ-520: Full Spectrum Smart Quantum Sensor (USB)
  8. Thanks for the feedback...good stuff!

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