How do I measure light distance with an uneven canopy?

[Kazman420]

Hi AFN,

Sorry for the stupid question but I'm curious how everybody measures the distance from their light to the top of the canopy when it's uneven. I did a good amount of LST and I got all my cola's fairly level, but between my two plants there are a few which are higher than the rest. I'd say they are about 3~4 inches above the rest of the canopy.

So where should I be measuring from? If I go from the top of the tallest cola then everything else is not getting optimal light. If I measure from the top of the canopy then I worry about the taller colas getting burned/bleached. Do I take an average between the two and go from there?

Comments and suggestions are always appreciated!

 

[JP1]

Put the shorter plant on top of something to make everything even

 

[Kazman420]

Put the shorter plant on top of something to make everything even

Heyas Jerseyphresh1!

The canopy is fairy even across the two plants, I'm talking about cola's within the canopy that grew a few inches taller than everything else.

 

[Bruce Campbell]

Error on the high side (while you can) and extend your light cycle by an hour or two each day.

Autoflowers have the advantage that we can extend the lighting hours to make up for low light intensity.

Eventually, the highest colas may get so close and/or you'll run out of height and start focusing on them. Once you start pushing their limits, their sugar leaves should taco from heat before the buds bleach:

You can also use leaf surface temperature as an indicator of potential light/heat stress. As they get closer to the light, radiative heating of the leaf will increase. If it exceeds the evaporative cooling from transpiration, the leaf temperature will be higher than the air temperature. You can decide on a max value to use to indicate "too close".

 

[JP1]

You can either just let them grow, keep tying them down, supercrop (very carefully) if they get out of hand, or put a net over the top and spread everything out. If your into flower, I'd just let it rock

 

[parsing_trees]

Rather than using the height distance between some point on the canopy and the light, I've found it a lot more useful to use a meter to measure light intensity in several places throughout the canopy, then reposition my lights and train to even those out. Even with the same vertical distance, movement off to the side will significantly decrease light intensity.

You didn't specify what kind of light you're using, but if you have modern white/full-spectrum LED lights, a ~$25ish lux meter will work quite well.

 

[Kazman420]

Error on the high side (while you can) and extend your light cycle by an hour or two each day.

Autoflowers have the advantage that we can extend the lighting hours to make up for low light intensity.

Eventually, the highest colas may get so close and/or you'll run out of height and start focusing on them. Once you start pushing their limits, their sugar leaves should taco from heat before the buds bleach:

View attachment 1380228

You can also use leaf surface temperature as an indicator of potential light/heat stress. As they get closer to the light, radiative heating of the leaf will increase. If it exceeds the evaporative cooling from transpiration, the leaf temperature will be higher than the air temperature. You can decide on a max value to use to indicate "too close".

Wow, thanks @KDawg for the awesome explanation! Love the picture with the tacoing leaf. Always nice to have a visual.

I check leaf temperature with my IR thermometer as part of my routine and it's consistently ~3 degrees lower than room temperature. (I say room temperature but I really mean the temperature under the light by the canopy). Now that I know what to look for I'm going to follow your advice. Much appreciated!

 

[Kazman420]

You can either just let them grow, keep tying them down, supercrop (very carefully) if they get out of hand, or put a net over the top and spread everything out. If your into flower, I'd just let it rock

Supercropping scares the hell out of me. I watched a video once and I couldn't believe the guy intentionally did that to his plant, hehe.

The girls are in flowering mode at this point so the net is a great idea for next time, thanks!

 

[parsing_trees]

Supercropping scares the hell out of me.

It's worth practicing so you won't stress about doing it the first time when you're addressing an already stressful issue. It's incredibly useful.

 

[Kazman420]

Rather than using the height distance between some point on the canopy and the light, I've found it a lot more useful to use a meter to measure light intensity in several places throughout the canopy, then reposition my lights and train to even those out. Even with the same vertical distance, movement off to the side will significantly decrease light intensity.

You didn't specify what kind of light you're using, but if you have modern white/full-spectrum LED lights, a ~$25ish lux meter will work quite well.

Heyas parsing_trees! I'm sorry, I forgot to specify my light. I'm using a 400w HPS. (I had the ballast and hood from a decade old grow attempt and just bought new bulbs). Upgrading to LED is actually on the top of my list of things to do. I just want to finish this one grow first.

I did try using a Lux meter app for my phone. I don't trust the numbers it gave but it did let me 'map out' the hot spots on my floor. (Not using a tent, it's a dedicated room in the basement). I do rotate my plants every time I fertigate. So twice a day they are adjusted to make sure they are getting equal lighting all around.