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    "The radiance from the cobs/leds need enough air (atmospheric gasses) between leds and the canopy to dissipate some of the energy out from the photons they’re emitting or the photons will dehydrate/fry the leaves when they hit them."

    This is not a valid explanation, maybe it's just missing IR in the spectrum. Colder leaves and high par make a bad combo. Otoh, i sometimes turn up my cobs and shine on the canopy with 37w/sqft and my plants can manage it with proper feeding and temperatures+humidity(vpd).

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      Originally posted by f-e View Post
      ButterflyEffect
      700ppm doesn't sound much really. Is that the 700 scale, making it about ec1.0 ?
      I did a run at 1.0-1.1 which was what keeping the runoff at 1.5max called for. I was 25% under target. My target being what know I can achieve when I'm not trying something new. I couldn't do that once a day, then water it down, even if that wasn't too run-off.

      The low P we spoke of has to be drip fed to waste every time, regularly. If not, then it's simply not there. It's been eaten.
      I guess if P is your only concern, you could put some in that evening watering. I feel the plant would be happier with a more continuous diet though.

      Stress training might involve dietary manipulation, but other than brushing the tops to limit stretch I don't practice anything like that. It's a bit like special teas. I don't practice voodoo, I'm saving up for my white smock
      As the clues start to come in, I'm seeing the runoff EC at, or just above input. In some rooms, the pH is down to 5.5-6, which is more in line with where it should be. I think you're right about the watering only. Osmotic shock maybe, so I'm designing the feed system to accommodate more frequent, but lower EC, fertigations. I run on the 500 scale, btw, so I'm around 1.2-1.3EC

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        Originally posted by Koondense View Post
        "The radiance from the cobs/leds need enough air (atmospheric gasses) between leds and the canopy to dissipate some of the energy out from the photons they’re emitting or the photons will dehydrate/fry the leaves when they hit them."

        This is not a valid explanation, maybe it's just missing IR in the spectrum. Colder leaves and high par make a bad combo. Otoh, i sometimes turn up my cobs and shine on the canopy with 37w/sqft and my plants can manage it with proper feeding and temperatures+humidity(vpd).

        Cheers
        This was the theory that I came up with, although I don't use LEDs outside of hybrid T5s in Veg. I'm hesitant to make the switch in a 4 room perpetual environment where I'm running CMHs and the ROI would be less impressive compared to HPS.

        It seems to me that in order to maximize Watts/SqFt, growers are moving the lamps close to the canopy trying to keep that DLI near 50W. Perhaps the local photosynthesis demands are too much given the lower transpiration levels. Maybe UV plays a part, too, I can't say.

        For me, I'll stick with my rock-solid CMH setup until I get bored later this year and convert one of the rooms over.

        Comment


          Hi folks had some yellowing after switch to bloom with my kingbrite lm301h+cree 660nm board(240w dimmed to 200) looked like fe deficiency for me.
          the soil mix is a one year used notill water only. Had already some prob in veg under 150w cmh osram powerball hci-t 942 but thats because of the low n levels imo. Prayer pupil was very light green and grew slowly.
          after i topdress a cup of a 50:50 kelp:shrimp mix everything looks better so far. Some tips are still yellow but everything is coming back to normal.

          Overall temps are a little lower but not much. i let the temp rise to 31°c before the vent turns to 100%. But i can say for sure the plants drink way less.

          Comment


            Hi folks i'm 2 1/2 weeks after flip and switch to qb leds.

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ID:	17817251 Since about a week its coming back. Already used some canna mg mono i had and the green color is coming back. The plants from clones show more sings of deficiency. The pic is 3chems

              Comment


                Originally posted by chilliwilli View Post
                Since about a week its coming back. Already used some canna mg mono i had and the green color is coming back. The plants from clones show more sings of deficiency. The pic is 3chems
                What is your pH?

                Comment


                  Can't say. I grow in 90l container with no drainage so i can't check. Also i don't trust those soil ph meters so i have no.
                  The last runs had no problems.

                  Comment


                    Those single probe Ph meters work pretty well. When the soil is wet, conductive, and you have a lot of Cation Exchange Capacity, the meter goes crazy and moves straight to 4 or 5 Ph, in 6.7 soil and 6.5 water. I call it "sparking". I started a thread about in organic soil. I may be full of shit, but it is what I am observing.
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                    Comment


                      I might try Mg from Epsom to see if it's the much forgotten sulfur. Doing so would also warrant some fe and could be applied as a foliage spray.

                      Have you depleted the N? I see leaf tips dying back and no fans. N doesn't always follow the classic bottom upwards, especially after the bottom has gone.

                      I would start with the spray as it's a quick answer.

                      Oddly I just had a crop wake up looking alarming yellow, but green up through the day. Day after day. As they filled the space the RH came up and it cleared. Below 50% was terrible. 55% wasn't satisfying. 60% fine. Though this was through transition so other things were going on.

                      I just can't get a humidifier during lockdown. I found whatever a sprayed on them greened them up though, even just water. I'm sure it was RH though a low pH can be interesting..

                      Comment


                        Yeah n is quiet low, made the mix a year ago. Veg was already slow and i used 5ml canna bio vega once and a cup of biovin(2.4-0.7-2.2) and got better grow.

                        My rh% is also low more 40-45%. I have a dehumidifier in front of the bloomroom set at 55% that is running but as soon as the air enters it drops.

                        Comment


                          total stoner theory but what if Mg was less mobile at lower temps than high temps? It's a metal and metals get colder faster (and heat up faster) than other elements.

                          I was thinking about Borosilicate glass where the simple addition of boron slows the rate at which glass cools and expands (Coefficient of thermal expansion), thereby preventing fractures (Thermal shock).

                          Maybe singular elements have a temperature range, like Mg, and effect mobility in plants? VPD rates are a ratio so maybe magnesium has a ratio of VPD and PAR energy?

                          Comment


                            Interesting.
                            Lately, instead of pulling out the measuring tape and making sure the LED light is at an exact distance from the canopy; I have been keeping the light back and letting the plant(s) grow into the optimal zone. I like the results so far. I see elongated kolas instead of golf balls in one controlled observation. Which is amounting to more weight in this one instance.
                            (Light was too close.lol)
                            *If you suspect your light is causing a deficiency try raising your light a few inches.
                            This thread is interesting.

                            Comment


                              your pics in that other thread where you say your plants are drying, looks like what plants do when getting too much light under LED’s.
                              back off the light, and you’ll see a huge difference.

                              I was keeping my 640w literally 4 feet away and @ 50%
                              only bump it up as they’ll allow, try not to start off too heavy rather too light.

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                              .
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                              Comment


                                Originally posted by TPFTFW View Post
                                your pics in that other thread where you say your plants are drying, looks like what plants do when getting too much light under LED’s.
                                back off the light, and you’ll see a huge difference.

                                I was keeping my 640w literally 4 feet away and @ 50%
                                only bump it up as they’ll allow, try not to start off too heavy rather too light.



                                .
                                Yes, this.. Most problems with white leds come from the lights being too close to the plants/lights are using too many watts for that distance= the leaves get dehydrated, esp. when the air is too dry all ready (winter season).

                                Coco/hydro growing is more forgiving under white leds cause there is more water in the plant tissue than when the plants are growing in soil.The coco-plant in my bloom tent has no issues at all with my Cree cobs when the soil grown plants are just on the limit of getting leaf damage (dehydrated, going abit pale and dry)


                                The only thing I had to change with my nutrient feed when changing to leds/cobs was adding calmag and Epsom salts, nothing more. No extra nitrogen or anything ,my NPK nutrients are exactly the same as under a HPS.
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