1.) It's not always the heat that's the issue it's too much light.
Many people tend to run 600w LEDs where they used to run 600w HPS lights and that's ALOT of light!
It depends.
Some 600 watt lights have the same uneven PPFD map that HPS does. Take a look at most of the HLG lights, for example. The max PPFD is in the center area and then values
collapse fall off when you move off center. The center of the grow will get decent light but the corners and edges are DAWA ("dark as a whale's ass").
Hang height is a big issue. Moving the light just 1" can make the difference between too much light and "just right". And hang height has a significant impact on how even the PPFD map is. The higher the light, the more even the light cast
but the lower the PPFD.
And then there's the dimmer setting. Most growers err on the side of caution because of conventional wisdom and FUD.
I can assure you: I run very low feeding schedules to the point where my bottom leaves show a lack of nutrients.
And still my tips are burnt, because that's how I figure out how much light they are willing to take.
I turn them pretty high to begin with and turn 'em back down as far as I have to, to keep my plants happy.
That's called "recon by fire".
Cannabis reacts to too much light by canoeing (or "tacoing") or by rotating the leaf around the petiole in the same way that a Venetian blind closes. In extreme cases, the photons will damage the cells in the leaf and the leaf will become brittle.
Leaf tip discoloration is a function of excess nutrients in the leaf tips. Why does that happen? It's a plant, nute ratios are a big off, nute levels are too high, VPD is off.
PPFD you ask? The values for my current grow are shown below. I measure daily (Apogee) and, as the plant matures, I sample multiple points. By mid-flower (next week?), when buds start to form, I'll sample the buds themselves.
The grow is a hydro grow, two Gorilla Glue in a 2' x 4 tent. Well ventilated and VPD is 1.0-1.2. Leaf temperature offset is -4 and ambient is 77-80. The plants are growing well and are tolerating >1kµmol.
Here's the entry from my grow journal:
Growcraft X3 running at 303 watts. SD is standard deviation which tells me that the canopy isn't very even.
A light meter can help - a Uni-T is $26 and it's easy to convert lux to PPFD (document attached).
These are pretty high light values and most growers won't give their plants this much light. OTOH, these values do indicate the amount of light that cannabis can use so, if you're not able to get your grow to these levels or maybe 90-95% of these levels, it might be worth it to work through the grow environment.
I think your approach is valid but I would not look to burned leaf tips as a proxy for light levels. Look at the other parts of the grow environment for a cause but do spend the $$ on a light meter and get your grow to 1kµmol. Cannabis is a
prodigious yielder at the level. (Not trying to be preachy-just a believer in feeding my plants well.)
I used "normal" light levels for about three grows but, by my third grow, the evidence about using high light was inarguable so I've been running high light since then.
2.) What about IR leds, they do produce heat!?
I suspect 730 will generate heat (I say that because it's in the "IR" spectrum) but, as always, it's not the poison, it's the dose. 730 diodes are still, unfortunately, not common in commodity lights and they're typically, very few in number.
Do they produce heat? Unquestionably. Do they produce enough to cause damage to the leaf as a result of heat? I would sincerely doubt. I've only seen one situation where a grower actually did damage to their plants and it was absolutely negligent.
3.) Don't forget your LEDs are not 100% efficient so yes the fixture also produces heat.
I have IR diodes and these huge blocks of aluminum on top of my boards with the drivers on top heat up quiet a bit.
I was actually wondering how my temps would look if I didn't have the IR leds running... but I can't turn 'em off sadly.
PS: No AC unit here yet, but if the summers are getting any longer or hotter I will have to think about it in the future.
Agree completely. Get an IR gun and shoot the temp of the bars vs the driver. I though the driver was the big source of heat but…
I have two lights (one veg, one flower) that use a 330 watt driver. Last Fall, the temps in the tent were getting too high so I starting switching to the driver outside the tent in later afternoon. Input wattage was probably 300+.
The temps in the tent still climbed.
The driver was 1'+ above the light bars and, between convection and the inline fan, the heat of the driver was leaving the tent. The increase in temperature in the grow zone was due to the light bars even though they were running at just over 100°.
Try the light meter and see what your PPFD values are. That tells you how much light is falling on your plant. What you're seeing with your plants reacting is the right approach - the meter tells you how much light your plant is getting but your plant tells you how much light it can use.
That's the important thing.
