COB LEDs - Is Too Much Light Counter-Productive or Just Wasted Energy??

Hello, after some googling it seems there are people who believe that too much light slows down photosynthesis which equates to slower growth. I think i read somewhere on RIU that a PAR over 1500 is just counter-productive in that it inhibits photosynthesis and slows down growth.

At the same time, i see people on RIU mention how they try to get their COBs as close as possible without getting any bleaching?

As a COB LED owner (twenty 3590s) i am wondering if getting our COBs as close as possible without getting any bleaching can be a bad thing?? In other words, worse come to worse, are we just throwing more light at the plant than it needs, or is it possible to actually slow down growth by having COB LEDs too close even though its not close enough to induce bleaching?

If they aren't bleaching - it's ain't bad. I noticed that they don't like that intensity when 24\0 but with 18/6 at about 8-10 inches it's awesome dark green with a lot of praying toward the light. I drive my cobs at 1.4A with 60 and 90 degrees reflectors. Colas that are sticking out of canopy due to not so equal stretch gets positioned right in between cobs.

If you put your COBs as close to the plants as possible until they start bleaching, you will end up way too close to get an even uniformity of light distribution. Directly under the COB the light would be very bright and between the COBs it would be a lot darker. That is not good for optimal growth over the whole grow area.

The height of the fixture should be determined by achieving the "optimal" uniformity. In general you go for a uniformity where the darker spots should then preferably still get at least 80% of that average. To check this, measure a matrix of points across the surface and calculate the average, then find the darkest spots and make sure these still get 80%.

Don't overdo it on the uniformity either and try to get more than 80% for the dark spots, because then your light would be too high which means you lose light on the walls.

You will have to go seriously overboard in watts to bleach your plants after you established the correct height.

wietefras said:

You will have to go seriously overboard in watts to bleach your plants after you established the correct height.

Click to expand...

Agreed, though there is a place between too much light and getting bleached where plants won't grow well. It's a rare issue but some of the recent threads talking about +1500 PPFD builds makes it worth considering. 1000 PPFD is pretty intense while still being on the safe side. The yield increase going from 1000 PPFD to 1500 PPFD isn't going to be huge so it's a matter of opinion on whether it's worth doing.

newguy41410 said:

it possible to actually slow down growth by having COB LEDs too close

Click to expand...

Get them as close as possible with decent uniformity and if the PAR exceeds 900-1000 µMole then crank the current down and save some electricity. With the CoB part number, grow area , and number of bars, I have an app that will find the ideal spacing and height for optimal uniformity.

You have a link to that app?I wanna try it

NoFucks2Give said:

Get them as close as possible with decent uniformity and if the PAR exceeds 900-1000 µMole then crank the current down and save some electricity. With the CoB part number, grow area , and number of bars, I have an app that will find the ideal spacing and height for optimal uniformity.

Click to expand...

link to app please?

newguy41410 said:

ink to app please?

Click to expand...

It is not on the Internet, it's running on XAMPP on my Win XP workstation.

I am going to put it online just for you. It would help if I knew what you setup is.

Basically I simulate a 48" bar of CoBs with 3, 5, or 7 CoBs per bar
You can set the height above the canopy, and the interval spacing between CoBs

I've been drinking since mid afternoon and doing adderall so kinda fucked up.
Recipe for a sense of humor, 3 Budweiser , 2 Adderall
I am now following you and @waynejohn
You guys message me and I will send you a link to the app.

I need some time to get it up online. Normally it would take a few minutes but I have zero concentration right now.

Here is another app that is a precursor to the other. http://growlightresearch.com/ppfd/dangles.php (dual angles)

This is a very cool app. Do a view source and you will see how I create the 6 SVG images. And it takes like a few millisecond to go from the 2 sets of numbers below and make these 6 SVG images. If you anything about programming, there is only one IF (no ELSE) statement in the entire program.

There are 20 LEDs that you can compare to one another. I have the each 10th degree radiant distribution for each. I fill in the rest, compute the flux for angles 90°-0° where are from sphere so I have to flatten them to flat earth.

There are two insets, the first (left most) is the angles from the datasheet, the second is the flat earth. I then compare the two selected.

If you get the datasheet to the listed LEDs these are the flux at 90, 80, 70.. 10,0 degrees.

While I put the other app online, read the attached PDF. I just started doing the documentation. It's kind of complicated to explain. I do not think you will get it from this but maybe. It is an incomplete rough draft with typos. If you know PHP programming that would help.

Message me and I will reply with a link. There are these guys on this site that are what I call "CoB snob cyber bullies". I do not want them getting the link.

The document is attached.


$pattern[1] = array(.98,.92,.84,.73,.60,.47,.34,.24,.13);
$pattern[2] = array(.99,.98,.98,.98,.97,.95,.94,.25,.06);
$pattern[3] = array(.98,.99,.99,.95,.88,.70,.40,.10,.02);
$pattern[5] = array(.99,.95,.88,.77,.63,.50,.33,.15,0);
$pattern[4] = array(.99,.98,.96,.89,.82,.74,.62,.52,.33);
$pattern[6] = array(.99,.95,.90,.80,.70,.50,.36,.12,.0;
$pattern[7] = array(.99,.96,.91,.82,.70,.52,.35,.15,.0;
$pattern[8] = array(.99,.94,.88,.81,.72,.60,.41,.11,.09);
$pattern[9] = array(.99,.96,.91,.81,.71,.52,.38,.20,.0;
$pattern[10] = array(.99,.94,.85,.75,.61,.48,.30,.11,.02);
$pattern[11] = array(.98,.92,.82,.72,.69,.61,.41,.23,.12);
$pattern[12] = array(.99,.99,.97,.82,.80,.72,.68,.58,.2;
$pattern[13] = array(.99,.98,.98,.98,.98,.98,.95,.35,.06);
$pattern[14] = array(.99,.96,.90,.82,.71,.52,.35,.13,.02);
$pattern[15] = array(.99,.96,.92,.87,.79,.62,.38,.17,.07);
$pattern[16] = array(.98,.96,.9,.8,.7,.6,.55,.2,0);
$pattern[17] = array(.99,.96,.9,.8,.7,.52,.35,.17,0);
$pattern[18] = array(.98,.95,.88,.78,.62,.47,.30,.12,.02);
$pattern[19] = array(.93,.81,.68,.50,.24,.15,.10,.06,.02);
$pattern[20] = array(.99,.98,.97,.92,.84,.72,.50,.20,.06);

newguy41410 said:

link to app please?

Click to expand...

It is online and working now.

This was taken a minute ago.

BTW, If you do not know Trig really well, the doc will make very little sense. If you know trig really well, you may understand.

Short answer, yes.

Light bleaching is a myth. Well more correctly it is damage from heat. That heat can be coming from the light being converted to heat as it hits the plant. If you cool the canopy to keep heat low and rh low, most plants can handle whatever you throw at them.

Whether you get better results with more is up for discussion.

i think the biggest shortcoming ive found from leds is low leaf temp. if you get a cold spell you just dont have the vigor that you would have with hids or even t5s heating up your leaves.

low metabolic rate+ low transpiration rate is a double whammy

i try to keep it warm and keep vpd 'correct' at the warmer temps, but at that point, at the air temps you need for good leaf surface temps, the humidity is dangerously high if you want "Ideal" VPD. It's playing with fire to be 70% RH in late flower

I can see why a lot of HID guys dont do well with LED if they dont adjust the environment

CobKits said:

i think the biggest shortcoming ive found from leds is low leaf temp. if you get a cold spell you just dont have the vigor that you would have with hids or even t5s heating up your leaves.

low metabolic rate+ low transpiration rate is a double whammy

i try to keep it warm and keep vpd 'correct' at the warmer temps, but at that point, at the air temps you need for good leaf surface temps, the humidity is dangerously high if you want "Ideal" VPD. It's playing with fire to be 70% RH in late flower

I can see why a lot of HID guys dont do well with LED if they dont adjust the environment

Click to expand...

I've been wondering if you could really stick to the ideal vpd range through flower without budrot. I was planning on dropping a decent bit under the ideal range since I wasn't able to find too much on it.

I've been trying to keep rh between 60-75% for my grow so far(temps between 70-85ish f), and once I see some real bud formation I'm going to drop it to probably 50-55% max I think

So @CobKits you are saying that my high temp okace 28c+plus 45rh is good thing?

CobKits said:

i think the biggest shortcoming ive found from leds is low leaf temp. if you get a cold spell you just dont have the vigor that you would have with hids or even t5s heating up your leaves.

low metabolic rate+ low transpiration rate is a double whammy

i try to keep it warm and keep vpd 'correct' at the warmer temps, but at that point, at the air temps you need for good leaf surface temps, the humidity is dangerously high if you want "Ideal" VPD. It's playing with fire to be 70% RH in late flower

I can see why a lot of HID guys don't do well with LED if they dont adjust the environment

Click to expand...

Agreed on temp. 85*f+ is pretty regular for me and have yet to "sacrifice any quality by doing so despite many myths and perpetuated BS.
But if you are following VPD then mold and mildews are not an issue. Spores will not germinate at the elevated temps that coincide with correct VPD. Stay in the VPD zone, and be fine.
Try and fight it...and you usually end up causing swings in temp and humidity.
Obviously airflow is your friend.

There are numerous studies showing the benefits of greenhouse screens and panels on production despite 30-50% reductions in light. As they fall more into growth ranges(700-1200mols) rather than borderline or total photoinhibition of 1500+.
As well as static lighting plays a role vs the ever changing incident angles of the sun that help distribute the massive solar light load on the plants.

CobKits said:

i think the biggest shortcoming ive found from leds is low leaf temp. if you get a cold spell you just dont have the vigor that you would have with hids or even t5s heating up your leaves.

low metabolic rate+ low transpiration rate is a double whammy

i try to keep it warm and keep vpd 'correct' at the warmer temps, but at that point, at the air temps you need for good leaf surface temps, the humidity is dangerously high if you want "Ideal" VPD. It's playing with fire to be 70% RH in late flower

I can see why a lot of HID guys dont do well with LED if they dont adjust the environment

Click to expand...

Im a HID guy who is struggling a bit with my cobs. 2 grows so far and i chased a cal/mag deficiency in both that really stuffed bud production after 4 weeks of bloom. Or.. maybe it was i let the pots get too dry and it was salt build up that got me. Hard to say...

Anyway... i was at a rock steady 77 to 79f and 40 to 50% rh all the way through both grows. Where should i be, ideally?

I don't understand where the low leaf temp thing comes in... guys put your hands under a COB @ only 50W at several inches I feel warmth... others are not? If you don't have the leaf temp then maybe your room is too cold to begin with.

I only get bleaching within a few inches (~3-5") of COBs at 50W. Running at lower current I could maybe get closer, running at higher current I'd expect that distance would need to grow to prevent bleaching. 6 inches directly under, or 3-4inches and a bit off axis from the COB source, and the bleaching is much less. Any closer and the bleaching happens, but at these distances the heat and temp is much higher. Play with the proximity/distance and temp/feeling with just your hand, now imagine a plant that doesn't get to escape that close proximity to a heat source.

I'm going to agree I believe it's the heat, as summer is here and my room is warming up, I'm finding the bleaching is happening at greater distance than it has through the winter in the same room.

Greengenes707 said:

Agreed on temp. 85*f+ is pretty regular for me and have yet to "sacrifice any quality by doing so despite many myths and perpetuated BS.
But if you are following VPD then mold and mildews are not an issue. Spores will not germinate at the elevated temps that coincide with correct VPD. Stay in the VPD zone, and be fine.
Try and fight it...and you usually end up causing swings in temp and humidity.
Obviously airflow is your friend.

Click to expand...

so youre saying most of the fungal activity would only happen during a cool night. I would think high RH/cool temps would be a lot riskier than high temps/low RH during the daytime. That humidity swing is kind of the rub too, trying to switch from a 85F/70% RH to a 75F/50% RH as soon as the lights go off. i know that people say inverse temp gradient can be benefical but my room isnt in the 80s with the lights off, i dont like my house that hot. i guess a big ass dehuey would raise temp and drop RH but im trying to be somewhat effcient.

CannaBruh said:

I don't understand where the low leaf temp thing comes in...

Click to expand...

use an IR thermometer and measure leaf temp in an HID room vs an LED room

CannaBruh said:

guys put your hands under a COB @ only 50W at several inches I feel warmth... others are not

Click to expand...

sure there is a little heat there, but my plants arent a few inches from the cobs they are 12-18" away with a fan jamming on them

Gquebed said:

Anyway... i was at a rock steady 77 to 79f and 40 to 50% rh all the way through both grows. Where should i be, ideally?

Click to expand...

i try to stay 85-88. in the past with HID if my room would hit 90 a lot of strains would donkey dick like crazy, i dont see that with LEDs (i dont try to run in the 90s but it happens once in a blue moon)

Diskokobaja said:

So @CobKits you are saying that my high temp okace 28c+plus 45rh is good thing?

Click to expand...

your humidity should be higher, search for "VPD" on the site or on google you'll find a chart. off the top of my head you should "ideally" be at 60-70RH at 28C, but as were discussing it might be a thing to be on the lower side just in case

What is optimal temp for leaves? I get mine at 25°C, room temp is 31°C at 60% RH.