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PAR Requirements

Discussion in 'Basic Growing Information' started by notforgodz, Jan 16, 2014.

  1. Tried doing a search but got kicked for not enough letters...even after using a phrasing a question and using a parenthesis.
    It occurred to me, while researching for induction and LED, what would be the PAR requirement for the bottom of the plant. So, what is the PAR requirement for a healthy marijuana plant?
    Krypto and chazbolin like this.
  2. PAR = photosynthetic active radiation.
    This is light between 400-700 nanometers. This spectrum of light known as PAR, is the only spectrum that plants use for photosynthesis.

    I'm not sure what u mean by PAR requirement? There is no such thing IMO. Its either u use light in that spectrum to grow plants or don't use it at all and grow nothing.

    I think what ur looking for is how can u provide ur plants with the highest PAR rating. At the same time take in to consideration umol/s count. This will let u know how many molecules of light are emitted per second. As far as the bottom of the plant, look into the calculations of how to determine the PPFD (photosynthetic photon flux density). Remember though that light intensity decreases as you move away from origin, so instead of worrying about anything growing on the bottom. Train or prune ur plants so that ur main growth is getting equal light throughout ur plant <<<< canopy management.Z
    kansabis, Homesteader, Krypto and 3 others like this.
  3. uMoles and Moles represent intensities, as in the number of photons of light within the PAR region are striking a meter squared per second. Based on the spectral distribution of the inda-gro 420 lights I use I target hybrids with an average of 20 mole/day. You can think of umoles as the number of raindrops hitting a bucket every second. Moles is how many inches of water accumulate within the bucket.

    You can learn alot from this paper but starting in the middle of page 16 you'll learn about umole and moles/day.
    kansabis, SecretKey, Krypto and 3 others like this.
  4. Thank you for your replies and excellent answers. It is obvious you guys know your stuff.
    So sorry for not correctly asking my question. I was tired and looking at some reference material on Induction/LED's dealing with a spectroradiometer. What I meant to ask is, what luminosity (or brightness) would the lower branches require for proper growth? I hope that this is the proper term... :)

    Theoneandonly Z, that is an excellent idea about trimming and kinda along the lines of why I am asking this question. Once I know what base intensity the plant requires, I can use my light meter to trim to depth.
    Krypto likes this.
  5. Unless I'm running vertical lighting I'll partially defoliate the lower 1/3 of my plants since not much light is going to get through a dense canopy anyway. Those canopy fan leaves are like little solar panels but they will block light. What light does get through will be a result of canopy movement and at lower intensities as a result of the distance from the light.

    When flowering at the tops I like to see a broad spectrum lamp (I get this with an 18" lamp-canopy separation) emitting 600-700 uMoles over my 13 hour lights on cycles. This gives me between 28-33 Moles/Day which from my experiences with Indica dominants has been ideal. If I have multiple lights and put the lamp-canopy distance @ 12-14" that same 13 hours will put me in the 40 Moles/Day region for Sativa dominants. There's a Moles/Day chart on page 17 of the link I gave you that will make this easier to understand.

    On a 4 ft plant with good canopy movement I aim to get an average of 200-300 uMoles at the lower flowering sites but unlike the canopy where light is a constant intensity this is going to be an irregular reading unless you LST. If I've got multiple plants running taller than 5 ft I'll run the vertical VPAR light, no defoliation and pick up the lower branches that way.
    Last edited: Jan 18, 2014
  6. Djb


    So you're going 13 11? Can you tell me why....I'm new at this
  7. Krypto


    That's what I do. It saves an hour of energy and to me it seems like the plants grow more in the dark anyway.
  8. Krypto


    Any recommendations on a good light meter? Sum of the measures the PAR, Kelvin, etc.
  9. so the PAR needed is 400-700 nanometers - so a 300 is rated 716 PAR at 12 inches / 312 PAR at 18 inches/ and 233 PAR at 24 inches > so I have good cover at 18 inches + Now with 2 45 watt 12by12 side panels night hadd afew PAR's _ AM I thinking on the right idea???, (for a bit it was LUmens - understand them but PAR is the realmeter) was going to buy a PAR meter and many reviews said they are junk .not getting one
  10. Yeah I haven’t been able to find decent par meter either. And going by what they say about par being between 400-700 nm still does not give an actual intensity. 400-700nm are colors not strength of the light.not anything to do with penetration power. Power is the deal. If par is what they re saying. it is more related to spectrum not how strong the light is. So I’m definately confused now.
    kansabis and hawkman like this.
  11. and that come's to 45 par per foot??
    Roscoe14 likes this.
  12. Get a Hydrofarm Quantum PAR meter for a $100+ which will give you the intensity of light in the PAR range or download a free lux meter app.
    hawkman and sixstring like this.
  13. Yeah something like that. I just try to put as much light as I can n back off if it looks like it’s burning or drying too much.
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  14. PAR is the range of color that photosynthesis uses. Anything out of that range and it is most likely wasted light in terms of photosynthesis. A PAR meter is going to give you the intensity of the light in ONLY that PAR range. If your light has UV or IR it is not going to get picked up on that meter.
    Last edited: Apr 18, 2018
    GT21 likes this.
  15. Nugg


    Maybe I understand what your after..I have two room both led,but different,lights...rm.#1 4-600 par.( Viperspecta) covering a 6×6 area..have to run sog.if your lights grow bushy plants light mine.lights don't really reach very deep 6" all lower gets trimmed...grow rm #2 uses 2-1200 w.( Mars hydro) covering 4×8 area 8 plants.these lights grow much taller bigger plants, but light still don't go deep so I run a v shape,so I cover 2 4×8 areas.....bottom line led= srogs.light is only knows one direction..??? Maybe I shouldn't have burnt one then started writing..
    Homesteader likes this.
  16. in relation to PAR - have you heard the if you use just the "blue" spectrum of led in last 3 days before harvest increase terpene's and essential oils. it like just blast'ens can give you reference to material if you want. checking on amason one can get 12by12 blue spectrum led panels for 40.00 AND even a blue led "regular" light for $80.00