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Lux and who goes by it

BB0420

Active Member
Hello,

I am currently growing with 6 qb96elites off of 3 HLG-320H-54A drivers. I wanted to know if anyone goes off lux I’ve been trying to go off it for my plants and think I’m doing something wrong here. I had my seedlings at 8,000 lux and they are yellowing and closing up. I just fed them some nutes I’m at 70 ppms now and I turned my lux up to 14,000lux. Let me know what you guys are doing to control your drivers accurately. I appreciate any advice. Thanks!!
 

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TorturedSoul

Member of the Month: May 2009, Oct 2010, Sept 2017
I wanted to know if anyone goes off lux

Well, since that - and all "lumen-based" measurements - are heavily biased/weighted towards those portions of the spectrum which the human eye (and, I suppose, the human brain) perceives as being brighter... My guess - and sincere hope, lol - would be: Very, very, very few gardeners. Since plants have neither human eyes nor human brains, those artificial units of measurement are more or less completely irrelevant. Here's a thing: Light sources that have a high percentage of their output in the green portion of the spectrum will score relatively high with such a measurement system - and we all know they also make really shitty grow lights.

If you're going to bother to do direct measurement of the (light-) output, don't use a measurement system that's really only relevant to architects, interior designers, and others who are concerned with the lighting/illumination of residential spaces - use a measurement system (and tool(s)) that is relevant to plants. Here's a basic Wikipedia article to get you started:

A well-regarded tool for measuring plant lighting is the Apogee MQ-500:

The Hydrofarm LGBQM is significantly cheaper ($150 to $175), but it's also considered to be fairly shitty by a lot of people, in terms of build quality and such (and owners would be well-advised to ensure the firmware is updated). Lots of reports of people addressing the poor design/build quality with a screwdriver and hot glue gun, lol. They also used to have issues with reading high, depending on the exact spectral mix of the light being measured, although this might (I have no idea) have been dealt with via firmware, IDK.
 

Nunyabiz

Well-Known Member
Lux meter readings can be converted to PPFD by a simple converter.
Not nearly as accurate but all I care about is accuracy within 100 PPFD.
I want my plant to get about 800-900 PPFD average across the canopy.
But I am fine with 700-1000.

Just use a Lux to PPFD converter and select what is your closest spectrum and you will get close enough as long as you're not using Blurple.
Lux meters wont read Blurple very well.

$30 vs about $500
 

The Celt

Well-Known Member
Hey @BB0420, as @Nunyabiz said, you can use a LUX meter to ballpark you PPFD values and will probably come as close as the hydro farm quantum meter.

If your LED is in the 3200k colour range, multiply by 0.017 to get your PPFD. In veg, shoot for 400 to 700 ppfd and in flower, over 700. If your light is a different colour, Apogee has a conversion page for converting LUX to PPFD on their site.
 

61FALCON

Well-Known Member
The hlg website has the info. Just divide the Lux value you are getting with the Lumens/PPF ratio to get the PPFD value.
QB 96 Elite V2 Lumens/PPF 66.4341 .
So just divide your lux reading by 66.4341 and that is your approx ppfd.
This is a good cheap lux meter. dr meter lx1330b s-l1600.jpg
 

BB0420

Active Member
Wow I appreciate all your guys comments. I was getting ready to buy a $550 par meter and very unhappy about it.. I use to run (2) viparspectras 1200w I know not the best lights but I got good returns and had no problems. I built my qb96 setup and just been having nothing but problems with seedlings. I’ve lost 4 sets of seedlings under these lights and not all were caused by lighting but still... I’ve just been unsatisfied with what I’m doing and I’ve been going off my lux meter and somethings still not right.

@61FALCON i actually am using this meter! So I just checked and I have 158.24 PPFD for seedlings.. seems probably good right?
 

61FALCON

Well-Known Member
Wow I appreciate all your guys comments. I was getting ready to buy a $550 par meter and very unhappy about it.. I use to run (2) viparspectras 1200w I know not the best lights but I got good returns and had no problems. I built my qb96 setup and just been having nothing but problems with seedlings. I’ve lost 4 sets of seedlings under these lights and not all were caused by lighting but still... I’ve just been unsatisfied with what I’m doing and I’ve been going off my lux meter and somethings still not right.

@61FALCON i actually am using this meter! So I just checked and I have 158.24 PPFD for seedlings.. seems probably good right?
This is from a growbro. I know you are in a 5x5 but you will get the idea.
For anyone using six 96s in a 4x4, here is a quick & dirty starting point for easy propagation thru harvest intensity:

Put your six 96s in the layout below, hang ~36”, @ 120w/light:

For prop - move one of the middle ones closer to the center of tent, turn just that one on, use your light meter to adj position so you get same perimeter intensity near all walls of tent, should be 100-150 ppfd across footprint, adjust dimmer to nail. Use this from cotyledons to 2nd true node, then switch to,

For early veg: put single light back to the original position, turn on both middle lights, this should give 250-300ppfd across the footprint, adjust dimmers to nail. Use this from 2nd true node to 6 true nodes, then switch to,

Mid-late veg: turn off middle lights, turn on 4 corner lights, this should give you 450-550ppfd across the footprint, adjust dimmer and/or ht to nail. Use this 6 true nodes till the end of veg (max 600 ppfd).

12:12: drop lights to ~18”, continue at 120w, turn on all 6 to get ~1000ppfd across the footprint, adjust dimmer 120-140w to nail. Keep light at 18” gap thru harvest...

If you use a lux meter to approximate ppfd:
put your lights-frame together, adjust wattage to 120w, measure lumens at 18” around your tent, divide lumens by 67 to get a ppfd approximation, should be close to my ppfd measurements in table for six 96s. If not similar, take lumens measured and divide by my ppfd at that location to get your meter’s ppfd conversion factor..
qb96 x6.jpegqb96 spectrum.jpeg:peace:
 
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