How much far red in my HLG 600 RSPEC?

I have a cheap APm130 PAR meter and an HLG 600 RSPEC.

In flower, when I try to get up and over 600 PAR reading I burn up and stunt my plants.

Researching around, it looks like my meter may not detect red light (above 660nm). And my light puts out a lot of light in this range.

How much? Can I calculate the amount and then mathematically adjust to find my true ideal PAR output?

Or do I just do it old school and eye ball things and gradually turn the light up as long as the plants "look good."

Soil Growth said:

I have a cheap APm130 PAR meter and an HLG 600 RSPEC.

In flower, when I try to get up and over 600 PAR reading I burn up and stunt my plants.

Researching around, it looks like my meter may not detect red light (above 660nm). And my light puts out a lot of light in this range.

How much? Can I calculate the amount and then mathematically adjust to find my true ideal PAR output?

Or do I just do it old school and eye ball things and gradually turn the light up as long as the plants "look good."

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Yeh, 600 is very low to be having issues.

Grow lights don't put out much 730nm light. Light in the wavelength induces cell elongation and that's not "a good thing" in cannabis growing.


I got the spectrum chart from the spectrum report on the HLG website for the 600 RSpec and ran it through Grok. The results are here.

The issue your hitting is a limitation of your grow environment. The only time I've seen a grow hit that limit was in the case of two soil grows where the plants maxed out at ~500µmol because the soil was hygrophobic due to poor watering practices. Any chance that's what's causing the issue for you?

Got any pics of the light stress you’re referring to? A pic of some plants under the lights can help as well.

What are your environmental readings when at 600+ ppfd?

Thanks guys.

The plants I'm having trouble with are in soil, and smaller (5 gal vs 7 gal) than I'm used to.

So soil moisture could be an issue.

Environment:
temps about 78-79 with lights on. Occasionally it gets a couple degrees warmer before the AC kicks in.

Humidity 48-50%. Occasionally it gets into the low 40s when the humidifier runs out of water.

Not 100% ideal, so I guess environment could be a problem too.

Damage: crispy leaf edges and stunted buds with decent color in the non burned parts.

Temps at 78 and RH in the 40's is a high VPD so your transpiration rate is about 50% higher than expected. If it drops to 40%, there's a lot of water leaving the plants very quickly. This chart assumes that leaves are 2°F cooler than ambient. Even a 1° difference makes a significant change in VPD and since VPD drives water uptake which drives nutrient uptake…

What about watering practices?

I've been hand watering. I guess about half a gallon at a time, every other day.

Soil Growth said:

Thanks guys.

The plants I'm having trouble with are in soil, and smaller (5 gal vs 7 gal) than I'm used to.

So soil moisture could be an issue.

Environment:
temps about 78-79 with lights on. Occasionally it gets a couple degrees warmer before the AC kicks in.

Humidity 48-50%. Occasionally it gets into the low 40s when the humidifier runs out of water.

Not 100% ideal, so I guess environment could be a problem too.

Damage: crispy leaf edges and stunted buds with decent color in the non burned parts.
View attachment 5475188
View attachment 5475189

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I dont think this is a meter or spectrum problem. Could it be K lockout? Its fairly common when adding too much calmag, and if your plant is in too high vpd its likely to overdrink and get too much nutes- causing lockout of K; yellowing and burning starting at tips.
The par meter response curve seems kosher:

I guess excess K could be an issue, I think my latest top dressing had some potassium sulfate in it. I didn't consider K issues because the top of the canopy looked at lot worse than the mid and lower leaves. And it's pretty much the same recipe I've used before.

But I guess if the plants are slurping more water than normal out of smaller than normal pots they could be getting more K than I'm used to.

Soil Growth said:

I guess excess K could be an issue, I think my latest top dressing had some potassium sulfate in it. I didn't consider K issues because the top of the canopy looked at lot worse than the mid and lower leaves. And it's pretty much the same recipe I've used before.

But I guess if the plants are slurping more water than normal out of smaller than normal pots they could be getting more K than I'm used to.

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Did the plants get dry frequently before these symptoms showed up? In little pots, if you do frequent dry backs that get “too dry”, a lot of mineral salts can build up in your soil and on your roots until you irrigate again and then they dissolve back into solution, but not always evenly or in the same ratios. Just a guess.

The plants just don’t really seam light burned like I’ve seen flower plants before. I don’t see any bleaching on the buds or leaf taco-ing that would indicate over-lighting. Not to say that increasing light intensity doesn’t increase stress, I’m sure it does. But I don’t think it’s the root cause of the stress.

Maybe check soil PH and aim for a more consistent soil moisture content just to get them to the finish line. At this stage since they’re already stressed, if you can improve your VPD just a little bit and get them drinking regularly, they should still finish out alright.

Soil Growth said:

I've been hand watering. I guess about half a gallon at a time, every other day.

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I drown my roots (hydro) but that doesn't sound like a lot of water, especially with the low RH. Your ambient temperature is fine but RH is pretty low. Shoot for 60% in veg.

Do you have pictures going back as far as a couple of weeks ago? I'm thinking this didn't happen suddenly.