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Thread: How many hours does my grow light need to be on if providing 250-300 PAR?

  1. #9

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    Yes if the plants were dormant and are just waking up you should be okay. Newly shipped and planted sundews often stop producing dew on existing leaves and will need to grow some new ones, but it shouldn’t take long!


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    Quote Originally Posted by TheGuru View Post
    After a lot of initial research I went with the Finnex 247 Planted+ SE

    I recommend you copy and paste that into Amazon or Google, because the "+" and the SE are important. It has true 660nm red LED's as well as the more common 460nm ranges, which plants need both. Also, After over 2 years of continuous running this thing hasn't lost a single light in the array. Lastly, it is sleek and thin and adjusts in length. Mine is over a 55 gallon aquarium but they do have the same model in different lengths.
    Good luck!
    This was very helpful. Using your model number, the standard size of a 55 gallon aquarium, and some Googling I was able to figure out a likely PAR value for comparison to my light. Thanks so much!



    That light is plenty powerful for what you are growing I would do at least 10 hours on though. Flytraps and sarrs love lots of light the Capensis will too but it will stunt its growth if you give it too much bright led (from plenty-o exp. growing under led) as for dormancy your flytraps will be just fine. Dormancy is a survival adaptation due to lack of light and bugs in cooler months. With that being said, your flytrap naturally experiences dormancy so ultimately for the most robust plant and longevity purposes dormancy even a short term what I call light dormancy is ideal. Skipping it once However will not kill the plant.

    What concerns me the most is that top hiding the light, those led units move lots of air and it may overheat it it isn’t getting enough air flow.
    Thanks. I'll keep an eye on the Capensis and adjust if necessary.

    I had some concerns about the heat too, so I kept a close eye on it. The top is mostly open with just some decorative metal, and the light has a really awesome fan on it. Temperatures on the top, side, and bottom of the unit never feel more than 80F or so, and it has the advantage of heating up the terrarium by a few degrees while it's on (never beyond 80F), which simulates outdoor daytime temperature deltas.



    Yes if the plants were dormant and are just waking up you should be okay. Newly shipped and planted sundews often stop producing dew on existing leaves and will need to grow some new ones, but it shouldn’t take long!
    I wondered if that was the case. I have a new leaf that was just starting to grow when I transplanted. It's just starting to open up now. Hopefully I'll see some dew this weekend.

    If I don't, should I be concerned?

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    I would just use a natural photoperiod, whatever that happens to be for the plants you're growing. I should note that 300 PPFD is likely more than most CPs will be able to utilize when grown indoors, based on research I've read on photosynthetic capacity in CPs.

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    Quote Originally Posted by nimbulan View Post
    I would just use a natural photoperiod, whatever that happens to be for the plants you're growing. I should note that 300 PPFD is likely more than most CPs will be able to utilize when grown indoors, based on research I've read on photosynthetic capacity in CPs.
    Do you happen to have a link to that research? I'd love to read a little more.

    I would love to use a natural photoperiod. Unfortunately, the grow light is almost blinding when on, and there are only 9 hours that I'm reliably out of the room (midnight til 9am). So I'd rather not shoot that 9-hour window unless absolutely necessary.

    I did some googling and found an article with a handy calculator that said that at 300 PPFD, I should be shooting for 12-14 hours.

    However, I went back and measured my light distance from 'ground' again, and found that it is 12", and not 18" like I was assuming. I think this is because I had previously measured it to the bottom of the terrarium without accounting for the height of the base and pots (duh). Going back to that same independent test I saw, that means I should actually be seeing closer to 600 PPFD. Plugging that into the calculator, 8 hours per day should be more than enough...assuming, of course, that the plants could utilize that much light.

    Remeasuring got me wandering. Are you supposed to measure the PAR value at 'ground' level, or at the leaves? At this point there's barely a difference of 1" for me, but I'm curious what the 'correct' way to do it is.

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    I'm afraid I don't have a link handy. I don't even remember how I found that paper.

    Light height should always be measured from the leaf canopy - basically the top of the plants.

    As for that calculator you found, I'd take the results with a grain of salt. While it might technically be correct (though I'm not sure where the target numbers for PPFD per day come from,) you do need to take into account that the plants do have a limit to how much light they can utilize. Some plants also need a correct day length for seasonal cues for flowering, dormancy, and such things, which is the main reason I just stick to a natural photoperiod. If you're growing subtropical plants as most CPs are, that would be 10-14 hours depending on the time of year.

    But i sounds like you're wanting to keep your lights on for a maximum of 9 hours per day so they aren't on when you're around? I haven't heard of anyone using that short of a photoperiod before so I think you're in a bit of uncharted territory. If you do end up trying that, let us know how it goes.

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    Quote Originally Posted by nimbulan View Post
    I'm afraid I don't have a link handy. I don't even remember how I found that paper.

    Light height should always be measured from the leaf canopy - basically the top of the plants.

    As for that calculator you found, I'd take the results with a grain of salt. While it might technically be correct (though I'm not sure where the target numbers for PPFD per day come from,) you do need to take into account that the plants do have a limit to how much light they can utilize. Some plants also need a correct day length for seasonal cues for flowering, dormancy, and such things, which is the main reason I just stick to a natural photoperiod. If you're growing subtropical plants as most CPs are, that would be 10-14 hours depending on the time of year.

    But i sounds like you're wanting to keep your lights on for a maximum of 9 hours per day so they aren't on when you're around? I haven't heard of anyone using that short of a photoperiod before so I think you're in a bit of uncharted territory. If you do end up trying that, let us know how it goes.
    I worried that might be the case. Then again, experimentation can be fun. I've been taking photos every few days and will, I'm sure, be asking questions based on them in the coming weeks. I'll try to remember to post back here in a few months or a year with a synopsis of how the 9-hour day went.

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