Having A Light Source Too Close

[DrPhoton]

Removed for security reasons.

[D.A.A.S.69]

Hey Dano, that's a great article, but all of yours are great, an informative, way over my head ,but I still love reading them.
You can tell easily ,when the lights too close, an they damn sure don't like it to close either, if your watching your plants.

[DrPhoton]

Yea reading your plants is very important. But one aspect that goes overlooked is that the point between the compensation point and photoinhibition, can go unnoticed. Because the plant wont always show signs. Typically the plant can have a lower quantum yeild from chlorophyll avoidance or non-photochemical quenching. External symptoms such as bleaching doesnt happen until photoinhibition has initiated and damage has happend.

Still lots of work to do though.

[D.A.A.S.69]

Yeah your right, damn near impossible to have everything right. Still what else you got but watching your plants as close as you can

[BlueBudz]

Great article! I have often had thoughts about this. Also another thing you could maybe add or talk about to help people with the correct distance would be the shadows of darkness having the light to close would create. Causing under growth to get less and top to get to much..
i love when things get me thinking.
Merry Christmas

[D.A.A.S.69]

I hear you BlueBudz, I like things that make me think, but I ain't like you an Dano, y'all got something to think with, I didn't get none of that. lol. MerryChristmas
PS- I'm still trying to figure out how to use a damn lux meter.

[RosettaStoned]

Good read!

[Weed Pharma]

Thank you so much, for this information. Best article i've read in a very long time:
Whenever you do anything with cannabis- you must consider basic plant biology, which often is overlooked on many forums/posts.


I typically shoot for around 700umols at the canopy, but only use the companies PAR information chart.
The range you provided 500-1000 umols sheds light (pun intended) on why so many commercial growers have a PAR of around 510-525 umols at the soil or lowest leaf surface, keeping the entire plant in the zone.

The cure for so many grow problems- is to move the light away and watch the plant recover on it's own!

[DrPhoton]

Yes i believe even just a basic understanding in plant biology can go a long way in horticulture.
Very right on commercial growers fixture heights. Quite often they hang their lights several feet high, as they understand about light physics and how light does not degrade and why uniformity is very important. They quite often only measure around 500umols at canopy like you say, but they will yeild the best out of any other setup.

I was a few hours in and was clearly getting very tired, the last half of the article needs work to improve readability. But i will leave that to later. There are also standing issues with embedded images on this forum.

[Vapo69]

Dude .....great read.......can anyone explained VPD to me in layman's please?.....thanks

[DrPhoton]

Vapor Pressure Deficit is the potential for water in leaves to move from a high humidity environment to a low humidity environment. Think of it like a towl drying on the cloths line. The towl is the leaves. Saturated in water. Gases and liquids want to move from high concentration to low concentration, which is what happens with the towl when it drys on the line. So the same thing happens with leaves and so moisture is vented out and creates water movement in the leaves and the entire plant because of the hydrogen bonds causing cohesion. So the movement of water is a completely passive process. Where as the movement of sap is partly active.

[Vapo69]

Dude..Thank you..........much appreciate the reading material, I'm going to tackle it soon

[DrPhoton]

My pleasure, happy learning.

[DrPhoton]

Omitted for easier readability and further information.

[KingKush]

So "lights close as you can till you see a negative reaction and then back off slightly" is actually flawed thinking?

Psh it's tough to admit you are wrong sometimes but you have inspired me to swallow my pride.
I have to agree that if a plant is using resources to make a defensive reaction it will not be making headway towards botanical excellence.
So the tops of my Kush are starting to be veggie with thick dark twisted leaves coming out of the bud. But just where it's riding the line. I raised my lights about 3" today. Immediately afterwards they stink vs. yesterday they didn't, just one observation.

Thanks Danofdanger for sharing. Keep it up.

[DrPhoton]

Exactly, thats what i was hoping would be interpreted. A plant may thrive with the "back off slightly after symptoms" method. But you could be holding back up to one third of usable energy that goes to waste. Of course you have to balance between good light placement and plant health. Because you can just as easily loose that much energy from having your light source too high.

Happy learning.

[jerry]

Some great info in this thread! Glad to know more about this now, I learned the hard way with keeping lots of extra distance for LED lights. Another benefit is the extra height will help give a little "safety room" during the stretch!

[DrPhoton]

Glad it helped

[Vapo69]

Hello Dan......Do you mind if I rip your article and post it on another forum.....its pertinent to what I said on there.....thanks Dan.......I wont post until you reply

[DrPhoton]

I updated it a few times after you posted it on that thread, i just want to reattack the thought experiement segment but for the mostpart im happy with it. Dont worry just edit the one on that thread, it wont change much after now.

[Vapo69]

dude......it would be easier if you joined AFN lol......im sure they would love your other articles too.....its pretty friendly over there, just a bit different to here

[DrPhoton]

Haha na i couldnt stand having to check on several sites, i chose this one because it was young and humble.

[roperman]

If only someone invented a way to measure the light on the canopy without an expensive PAR meter. Is there any way to gauge the light without one? A way to measure 500 umols using some hack? I would love to see some sort of "sensor" paper. You put the sheet of paper on the canopy for 10 minutes, remove, and check the color. Just like pH strips.

[DrPhoton]

You can buy just the PAR sensors and connect them to a multimeter. Cheap and effective hack. There are some tutorials on youtube i think.

[DrPhoton]

I understand that the references of cannabis photosynthetic characteristics in micromols are useless to those who do not have quantum meters. As such i will provide tools to enable calculations of umols to lux. Where lux is the more common choice of measurement among growers.

Here you can apply conversion factors for light metrics such as photons in umols to lux. When applying the conversion you must select the right light source in order for accurate conversion factor. If you have an LED light source you can apply these conversions with satisfactory accuracy, if your LED system has white diodes. This is because the spectrum is very identical to that of high pressure sodium. If the color system is anything other than white, then the reliability of accuracy will go down.

For reference i will restate the cannabis photosynthetic characteristics in lux for HPS and white LED's.

Cannabis starts to saturate at around 500umols or 40,000 lux. The best range for photosynthetic efficiency is between 500-700umols or 40,000-58,000 lux. With the highest levels to be no higher than 1000umols or 80,000 lux.

Hope this is helpful.

[Paracelsus]

DrPhoton Subbed and understood

i have no meters I use the back of my hand right now till I do with my 4x48 T5 bank each tube is 54W 6500K
could you tell me the uMol for that and if I understand you right adding 6 more for a total of 10 bulbs will only increase the foot print but not the intensity. Is that correct?

[DrPhoton]

Certain light technogies have varying levels of electrical efficiency with respect to certain wavelengths. This is why green LED diodes are not used because they have the lowest electrical efficiency. For fluorescents, different color temperatures will have slightly different photon flux values. Which is more efficient i do not know, however i would wager the higher the color temperature the more efficient. Because fluorescent lights naturally produce UV light and is converted to visible wavelenths through fluorescense. So the closer the wavelength to its natural output, the least energy is wasted. But i dont know for sure.

[Paracelsus]

Thanks Dan I Believe 6.5 K to 7K is the range for what is called white daylight. Which gives me another query, I knew I shouldn’t write one more question LOL. In your opinion what is preferable, my 10 bank of T5 lights or direct sunlight through double pane thermal glass. I get direct eastern sunlight it till 12 noon on a sunny day it is spectacular but I’ve heard glass could take out the spectral rays. I know that I am asking a very technical question so I’m just asking your opinion thanks this is been an interesting morning have a great day.

[DrPhoton]

Ask away, no problem.

It would depend where you are and what time of year it is. Using this visual graph you would take your locations DLI and halve it because you only recieve half the daily sunlight. Compare that value to the DLI of your fluorescents which is 25mol per day.

I would probably still use fluorescents regardless.

[Paracelsus]

Thanks I know they like the Sun, they eat it right up. I’m going to figure it out thanks for the resources. My zone in April is 30-35 divide by 2 say is 15. Right now because they are juvenile in veg I only use 4 tubes that would be 10 uMol. iOS that correct? Also there is less morning light then afternoon it is close and a insignificant amount either way. Am I wrong?

[DrPhoton]

Improved readability and added further information.