Light intensity for autoflowering plants (lux)?

Srfr

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@Srfr,

Not sure what you are referring to. What exactly are you doubtful about, that it's possible to use a LUX meter to tell if the amount of white light hitting your plants is equivalent to full sunshine, hazy sun, or deep shade. Or what.
What I've read is Lux meters look at the full spectrum and grow light's primamrily push out the PAR spectrum. This makes them inaccurate. What I find them good for is consistancy. I cant afford a par meter but I do have a lux meter which I use less and less BUT it does allow me to get in the ball park. I hoep that makes sense. Best of all is to watch your plants. I like to see the leaves reachin up just a little towards the light but not stretching too much.
 

The Iconoclast

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@Srfr

What I've read is Lux meters look at the full spectrum and grow light's primamrily push out the PAR spectrum. This makes them inaccurate.

Well we've all read the same articles and watched the same technical videos so we all have the same data. The question is how does one interpret that data. And this is where you're pretty well on your own you just have to test stuff out in your own controlled environment. But that is really really time consuming as well as a lot of work and you build up your knowledge very slowly and for what purpose?

It is in the interests off all the people selling nutrients and lights and additives to just keep up this endless distraction, because the things that we as growers really, want to know once we know how to grow good quality, is what is really going on. We see one branch produce a massive bud and we wonder why didn't the branch next to it produce the same bud, what is it precisely, what hormones, what cell signalling, and how the plant interprets and reacts to this.

And what tends to happen I think is that to substitute for not knowing we obsess over easy to digest and easy to understand PPFD charts as if that is where the funk is. But if you want to know where the funk is you have to ask James Brown.

For example when we top a plant, or remove a giant early leaf, we are mucking around with the instruction hormones that the plant will be sending out, but we're only trying to make best guesses based on logical inferences. Plants have different manner of triggers and we want to understand that.

So back to the thread topic if you're using white lights which as basically all the same with regard to light quality, then a cheap 20 dollar LUX meter is all you're ever going to need. However going through this madness is all a part of the growing process.

Look at it this way, even if you could design the exact spectrum you wanted you wouldn't know what is the very best spectrum over different parts of the grow, all you could do is read millions of opinions and do whatever makes you feel warm and fuzzy, but we still won't have the answers to the questions that we really want to know.

We see a lettuce grow in a red mono light blue mono light and white or even green light, then we try and extrapolate that somehow down to different spectra for cannabis, it's madness really because this becomes important only when we know a whole bunch of other stuff first.
 

The Iconoclast

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However...

Having said all that, there is a big difference between say a fairly even scrog being lit, and a small open indoor grow space like a laundry or whatever where you can have plants in various stages or making more natural shapes, in this case you might want to go up to 70k lux in parts in order to get lower bits lit to your satisfaction. Again, a lux meter rather than a par meter is what is needed in this situation. If you're running a flat scrog and want to light a fairly flat area, you don't need any light meters you can go by the numbers.

This is the way I see it these days.
 

Kyote

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I use a lux meter only for reference which I can either apply or adjust on upcoming grows. Seedilings, I find 12k is a nice spot for a week or so, then up to 20k .. in full bloom, 50 to 60k is what i want to see right now.

Direct sunlight measures over 100k, but I'd guess the average during the outdoor grow is closer to 40 to 60k. I'll monitor that a bit more this outdoor season.
 
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Srfr

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My Mephisto auto plants just finished and could not tolerate anything over 30k lux. Mars hydro sp250.
 

Dosmokethereefa

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Theres a New app out in the google playstore called PPFD seems to be sufficient for us amateurs :headbang:
 

tronN00dles

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From my understanding, lux is dependent on the spectrum of your particular light. So 40k lux in one tent may differ from 40k in another tent. Hence, don't go by guides you see online. For my first grow, I read somewhere that 20k for seedlings, 40k for veg and 60k for flowering is a good rule of thumb. I followed this with my HLG 135 LED's and ended up with very short, burnt plants. This was much too high for my LEDs.

As PPFD values are well established, I'd recommend is to look for PPFD to LUX calculators online. They often approximate various lighting spectrums so you could get a better approximation of your light requirements. Better yet, check and see if your manufacturer has something similar. In my case, HLG actually has a PPFD to LUX calculator that accounts for their precise spectrums. In my case, my recommended range for flowering is 32k - 47k, and as low as 5k - 12k for seedlings.

Also, regarding the smartphone apps. I have a dedicated lux meter, and have tried apps on both Apple iPhones and Samsung Galaxy. The galaxy device reading matched my standalone lux meter almost exactly, where as the iOS app came no where close!

-tronN00dles
 

damien50

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From my understanding, lux is dependent on the spectrum of your particular light. So 40k lux in one tent may differ from 40k in another tent. Hence, don't go by guides you see online. For my first grow, I read somewhere that 20k for seedlings, 40k for veg and 60k for flowering is a good rule of thumb. I followed this with my HLG 135 LED's and ended up with very short, burnt plants. This was much too high for my LEDs.

As PPFD values are well established, I'd recommend is to look for PPFD to LUX calculators online. They often approximate various lighting spectrums so you could get a better approximation of your light requirements. Better yet, check and see if your manufacturer has something similar. In my case, HLG actually has a PPFD to LUX calculator that accounts for their precise spectrums. In my case, my recommended range for flowering is 32k - 47k, and as low as 5k - 12k for seedlings.

Also, regarding the smartphone apps. I have a dedicated lux meter, and have tried apps on both Apple iPhones and Samsung Galaxy. The galaxy device reading matched my standalone lux meter almost exactly, where as the iOS app came no where close!

-tronN00dles
Spectral distribution conversion will give you precise PPFD to LUX values but you are correct that it is unique for each light. The online calculators are very general with the only real way being to use a goniophotometer or a PAR meter or just follow manufacturer suggestions.
 
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