How do I measure light distance with an uneven canopy?

[parsing_trees]

Heyas parsing_trees! I'm sorry, I forgot to specify my light. I'm using a 400w HPS. [...]

I did try using a Lux meter app for my phone. [...]

I haven't used an HPS. A lux meter will probably work with them, but I haven't checked. The main case where they definitely won't work and you'd need a PAR meter (which cost ~20x as much...) are the red+blue/"blurple" LED lights, which have very different light than what the meters are calibrated for.

A lux meter app won't be accurate, because the phone doesn't have the sensor hardware set up properly for that use -- there isn't the translucent plastic dome for cosine correction, etc., so the phone's sensor readings will be overly sensitive to tiny changes in angle or position. Basically, you're measuring direct light through a pinhole, but for growing what you really want to measure is light reaching a wider leaf surface area from all angles.

 

[Cerebral Goo]

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!

Try practicing on some plants in your yard(if you have one). Actually, the neighbors plants are better!!! If you don't have a yard try a park etc...It's pretty amazing how pliable plants can become. Definitely gave me the confidence

 

[Kazman420]

I haven't used an HPS. A lux meter will probably work with them, but I haven't checked. The main case where they definitely won't work and you'd need a PAR meter (which cost ~20x as much...) are the red+blue/"blurple" LED lights, which have very different light than what the meters are calibrated for.

A lux meter app won't be accurate, because the phone doesn't have the sensor hardware set up properly for that use -- there isn't the translucent plastic dome for cosine correction, etc., so the phone's sensor readings will be overly sensitive to tiny changes in angle or position. Basically, you're measuring direct light through a pinhole, but for growing what you really want to measure is light reaching a wider leaf surface area from all angles.

That actually makes perfect sense about the phone app not being accurate. I believe you're correct that traditional LUX meters work with HPS (and I would think MH as well). I am planning on upgrading to LED after this grow. I didn't realize lux meters also worked with the (non-burple) LED's. That's great news. I'll check some sites/stores and buy a cheap ~$30 meter. Thank you for the reply!

 

[Bruce Campbell]

That actually makes perfect sense about the phone app not being accurate. I believe you're correct that traditional LUX meters work with HPS (and I would think MH as well). I am planning on upgrading to LED after this grow. I didn't realize lux meters also worked with the (non-burple) LED's. That's great news. I'll check some sites/stores and buy a cheap ~$30 meter. Thank you for the reply!

A lot of people go with the UNI-T because of MIGRO:

https://www.migrolight.com/cheap-par-meter-hack-use-a-lux-meter-to-measure-par-accurately/

 

[Kazman420]

Try practicing on some plants in your yard(if you have one). Actually, the neighbors plants are better!!! If you don't have a yard try a park etc...It's pretty amazing how pliable plants can become. Definitely gave me the confidence

Hey that's a great idea! There's a small park just down the block, hehe. I'm going to have to take a look and see what's there. Getting some practice would definitely help my confidence. I know the Mango Smile seeds which I bought can supposedly get VERY tall, so supercropping will become a necessity when I start that grow.

 

[parsing_trees]

A lot of people go with the UNI-T because of MIGRO:

https://www.migrolight.com/cheap-par-meter-hack-use-a-lux-meter-to-measure-par-accurately/

It's hard to overstate how handy it is to have the sensor on a longer cord, so you don't need to read a screen an arms length away and with glare from the lights.

I use a Dr.meter LX1010B, which works fine and was about $25. There are probably several other good options at around that price point, though.

 

[Delps8]

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!

I went with the average of the light falling on the plants directly under the light.

I'm 30 days into a Gelato AF grow and I started thinking about this same issue a few days ago. The plants are in a 35 gallon Superponics res, lined up underneath the Mars 3000. The plants are located 12" and 4" from the center of the res, two plants on each side of center. Hang height is about 15".

I took 12 measurements using the Apogee's sample function and put them into a worksheet in my grow journal. The plants are short - lots of blue in the Mars - and these measurements were taken at the leaf tops at the back, center and front of each plant.

Looking at the numbers below, what's my PPFD - do I use 582, 498, or 404? I decided to go with 498 as a representative number but it sure was an eye opener to take the readings and see that moving from the center of a plant to the front of a plant could cause the light level to drop 50%.

 

[Delps8]

A lot of people go with the UNI-T because of MIGRO:

https://www.migrolight.com/cheap-par-meter-hack-use-a-lux-meter-to-measure-par-accurately/

Going back a couple of months, Migro started selling an inexpensive PAR meter. I think it was in the $250 range. In that price range, I'd go with that one instead of the meters on Amazon. I figure Shane will stand behind his products but the ones on Amazon looked a little hinky.

 

[Kazman420]

I went with the average of the light falling on the plants directly under the light...

Looking at the numbers below, what's my PPFD - do I use 582, 498, or 404? I decided to go with 498 as a representative number but it sure was an eye opener to take the readings and see that moving from the center of a plant to the front of a plant could cause the light level to drop 50%.

I also decided to go with the 'average' height of the canopy since there's no way it'll ever be perfectly even.I broke down and ordered a Lux meter since all I'm doing is playing a guessing game with numbers. It doesn't arrive until the end of the month, but at least now I'll be able to have an actual idea of how much light they are getting.

I never would have expected that much of a drop in light from such a little bit of movement. Fascinating!

 

[Organic_Auto_Canuck (OAC)]

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!

I never tried supercroping autos. I assume I would do it once a week in veg after it's about 8 inch?