Have a 2 x 4 grow tent with an Agrogrite t5 4 ( 4 - 54 watt bulbs ) bulb light in it , I took two bulbs out . With my lux meter telling me I have about 37/42,000 at plant height i should be about max they can take ? They seem to be rather long and as if they are reaching for light . This is are second grow so still learning alot .... Ideas or thoughts ?
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3 week old seedlings
- Thread starter baddog
- Start date
DoctorJohnson
New member
I'll guess that you're getting that 40,000 lux reading close to the tubes. That's a good number for a small plant, but when it get's bigger you will have to think about average lux spread out over the whole grow space, of course, not just the lux reading right under the bulb.
Just doing some back-of-the-envelope calculations, you have two 5000-lumen tubes over eight square feet so 10000 lumens over .75 square meters so 13,000 lux if the light is distributed evenly, which is not enough. With all four tubes you'd be up to 26,000 lux average, which is better but not great. (There are corrections for spectrum, etc., but let's not over-complicate things here.)
Another way to look at it is just the number of watts (That calculation drives the purists with expensive PAR meters crazy, but it's good enough to get in-the-ballpark numbers). 100 watts over 8 square feet is about 12 watts per square foot, which is not enough. Again, even with all four tubes in, you'd only be up to about 25 watts per square foot.) I did a small fluorescent grow in which I had about 170 watts spread over about two square feet so 85 watts per square foot, and that worked well (i.e. a small plant with dense, sticky buds).
If you don't have a lot of experience with this, what can be deceiving is that you can grow a nice looking, healthy plant with a lot less lux than is ideal for the best yield. The problem is that the flowers just don't get very sticky. For example, I grew a very pretty plant outside last year (the same strain that did so will at 85 watts per square foot) that only got full sun for about half the day. It looked great, but the flowers had few trichomes and the sugar leaves around them had almost none.
So fiat lux!
<edit>
> They seem to be rather long and as if they are reaching for light.
Listen to your plants. They seem to be telling you they want more.
> With my lux meter
You're using a real lux meter, right? Not some silly-ass iPhone app? Trust me, you can't trust a camera converted into a reflected light meter. I have some experience in photometry and have used a real lux meter and an iPhone meter side by side and couldn't get reliable readings with the app at all.
You can get a perfectly adequate white-light meter at Amazon for $16. https://www.amazon.com/Leaton-Digit...1_1_11?s=photo&ie=UTF8&qid=1519498551&sr=1-11
Here's nebula on light meters: http://www.growweedeasy.com/lux-meter
OK, I've typed off my morning caffeine buzz. Time to go tend the white widow.
</edit>
Just doing some back-of-the-envelope calculations, you have two 5000-lumen tubes over eight square feet so 10000 lumens over .75 square meters so 13,000 lux if the light is distributed evenly, which is not enough. With all four tubes you'd be up to 26,000 lux average, which is better but not great. (There are corrections for spectrum, etc., but let's not over-complicate things here.)
Another way to look at it is just the number of watts (That calculation drives the purists with expensive PAR meters crazy, but it's good enough to get in-the-ballpark numbers). 100 watts over 8 square feet is about 12 watts per square foot, which is not enough. Again, even with all four tubes in, you'd only be up to about 25 watts per square foot.) I did a small fluorescent grow in which I had about 170 watts spread over about two square feet so 85 watts per square foot, and that worked well (i.e. a small plant with dense, sticky buds).
If you don't have a lot of experience with this, what can be deceiving is that you can grow a nice looking, healthy plant with a lot less lux than is ideal for the best yield. The problem is that the flowers just don't get very sticky. For example, I grew a very pretty plant outside last year (the same strain that did so will at 85 watts per square foot) that only got full sun for about half the day. It looked great, but the flowers had few trichomes and the sugar leaves around them had almost none.
So fiat lux!
<edit>
> They seem to be rather long and as if they are reaching for light.
Listen to your plants. They seem to be telling you they want more.
> With my lux meter
You're using a real lux meter, right? Not some silly-ass iPhone app? Trust me, you can't trust a camera converted into a reflected light meter. I have some experience in photometry and have used a real lux meter and an iPhone meter side by side and couldn't get reliable readings with the app at all.
You can get a perfectly adequate white-light meter at Amazon for $16. https://www.amazon.com/Leaton-Digit...1_1_11?s=photo&ie=UTF8&qid=1519498551&sr=1-11
Here's nebula on light meters: http://www.growweedeasy.com/lux-meter
OK, I've typed off my morning caffeine buzz. Time to go tend the white widow.
</edit>
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I'm getting that 40,000 right next to the plant with a Dr.Meter lx13330b . I agree with your calculations and what the plant is telling me and I will put the other bulbs back in . My lux meter appears to be working correctly as I move it into a darker area it does drop down and up in values as move it closer to the light . I have a bigger grow tent with led's where these will go when there bigger . Thanks for the help !
DoctorJohnson
New member
That meter is better than mine. Too bad it's only for white-ish light.
You could save yourself a little money by just using a 15 watt LED light bulb or two for the first few weeks. Good luck and have fun.
Too bad it's only for white-ish light.You could save yourself a little money by just using a 15 watt LED light bulb or two for the first few weeks. Good luck and have fun.
D.A.A.S.69
New member
You must not have the lights close enough, if they are still stretching, when I use cfls for my seedlings, I put them no further than 2inches away, and they don't burn anything.