Myth busters its the light

desertrat said:

you're running at over 20,000 lumens per square foot at 12 inches from the bulbs of the 600's - so that's pretty high compared to the recommended range of 7000 to 10000 lumens per square foot. But I've come to doubt the recommended ranges and your post is just more evidence.

Do you see any signs of leaf bleaching directly under your bulbs? Have you ever put the lights closer and seen bleaching?

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yes i am seeing some heat stress and bleaching, just in the last 2 days. we have hit 90+f both days and my room is around 88 during the hot times.i have only had the dual tube for 2 weeks,i raised it up last night so we will see.i'll go with 16" for a few days and let you know how they respond to it.

Denofearth69 said:

Hey desertrat, Let me open that ol' LED can of worms. I've been using LEDs to veg, and a combo of LEDs and floros to flower, and thus far I like the results especially in veg, as LEDs seem to have really good penetration to the bottom of the plants, and nodes are very close together. Also clones really thrive under LEDs. The place I bought mine from www,thegreenleaf.biz has some information regarding the different wavelengths of light that plants need, and how LEDs address this need. Also, their info says that LEDs have to be measured with a PAR meter, and not a standard light meter. This, they suggest, is because LEDs read low in lumens, but high with a PAR meter. Not sure what a PAR meter reads, and just wondered if you knew anything about that.

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leading edge vs bleeding edge. Personally not convinced we've heard the last word on which frequencies are used by the plant so I believe it's premature to start measuring light energy from limited frequencies. And I'm a great believer in wiki learning a little from a lot of people and I haven't seen a stampede of people for LEDs yet. I'm sure we'll hear about it and see it when someone does an led only grow and gets comparable yield per watt figures.

OZUT said:

Reps first brother...not everyday when someone posts something useful like this...

I actually tried this on my last grow...pushed it to the max....I had (4) 600's running in a 5x14 area and decided to mess around with the distance....With one of the lights, I had the tip of the plants less than 2 inches from the glass...figure the bulb is a couple of inches from the glass, the tip of the cola was less than 6 or 7 inches from the source...The master kushes didn't take too well and I think it was just too much light for it to process but the white widow/banana kush right next to it exploded with growth...It really took the distance well....The master kushes under the other lights that were at 12 inches were amazing, so I think it depends on the strain and not all of them handle the distance the same.

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Im sure strain plays a part but also you can only fit part of one plant directly under the light and for the other plants you have to take into consideration the horizontal distance to the bulb which means they were more like a foot away and getting much less light than the plant under the light.

desertrat said:

Im sure strain plays a part but also you can only fit part of one plant directly under the light and for the other plants you have to take into consideration the horizontal distance to the bulb which means they were more like a foot away and getting much less light than the plant under the light.

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This one I had the main cola at almost an equal distance just to see if strain makes a difference and because my master kushes were not very resistent to stress and bugs so I wanted to see what else they couldn't handle.

desertrat said:

leading edge vs bleeding edge. Personally not convinced we've heard the last word on which frequencies are used by the plant so I believe it's premature to start measuring light energy from limited frequencies. And I'm a great believer in wiki learning a little from a lot of people and I haven't seen a stampede of people for LEDs yet. I'm sure we'll hear about it and see it when someone does an led only grow and gets comparable yield per watt figures.

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Yeah, I have to agree. As much as I am impressed with veg growth using LEDs, I have to admit that, as a total newb to indoor growing, I caved to the many posts that said I would harvest very little if I used LEDs exclusively. As a long time outdoor grower, I have to sing the praises of the great grow light in the sky. Absolutely nothing compares, and that is even considering that you only get a maximum of 14 hours a day from the sun.

if i may ask desertrat where you got your reflector?(brand and what style) that and how is ur room set up. if ur 600w bulb is sitting alone in a dark walmart then that may have something to do with it. from and if i do remeber correctly mj responds more to the wavelegnth and intensity of it. "lumens are for humans" u may have heard. firm beliver of the super hps/mh bulbs. the mh especially. not tryin to piss ya off bro but do intend to ruffle ur feathers a bit. goodtimez

Stoneshield said:

if i may ask desertrat where you got your reflector?(brand and what style) that and how is ur room set up. if ur 600w bulb is sitting alone in a dark walmart then that may have something to do with it. from and if i do remeber correctly mj responds more to the wavelegnth and intensity of it. "lumens are for humans" u may have heard. firm beliver of the super hps/mh bulbs. the mh especially. not tryin to piss ya off bro but do intend to ruffle ur feathers a bit. goodtimez

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Not sure why you care about my reflector as i am taking measurements without one when describing the physics of light. I do of course use a reflector for growing, but again, how can it matter? Using a reflector greatly complicates meayrements because you are then dealing with the combination of a direct point light source and diffuse reflected light.

As for light wavelengths being important, the literature claims plants differentially absorb light in the 400 to 700 band but I have not seen any empirical data to back up that claim with real world differences in growth rates. Lumen measurenents overlap that range but include some other frequencies. Par measures in the 400 to 700 band but ignores potentially useful light outside that range. I'm going to stick with lumens as a surrogate for what the plant uses until I see evidence that plants don't use broader spectra of light. I'll probably come back at the end and do some par or broad spectrum light measurements as a further check.

Thanks again for all the information and knowledge.

OZUT said:

This one I had the main cola at almost an equal distance just to see if strain makes a difference and because my master kushes were not very resistent to stress and bugs so I wanted to see what else they couldn't handle.

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Ok, thanks, that's really helpful. Anyone else with experience of different strains handling light differently?

What I was wondering and you might have some insight on this, can you taste a difference in smoke from the ones that are closer than 12 inches? I've tried this some people have said the ones that were closer lost some flavor...I have a group I use to test every batch I do and I always save a little from each batch for future comparison....Now I'm not sure if they did taste different or if it was psychological because I had guided them through the smoke and they some how were looking for a difference...

Here's a picture of the master kush cola....not a good picture but you can see how it's airing out....It was massive (I was longer than the distance from the tip of my finger to my elbow)....But the last 10 days it just started airing out when it should have fattened up

Forgot to add that the 2nd picture is the other strain (cross between White Widow and Banana Kush)

OZUT said:

What I was wondering and you might have some insight on this, can you taste a difference in smoke from the ones that are closer than 12 inches? I've tried this some people have said the ones that were closer lost some flavor...I have a group I use to test every batch I do and I always save a little from each batch for future comparison....Now I'm not sure if they did taste different or if it was psychological because I had guided them through the smoke and they some how were looking for a difference...

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I haven't noticed a taste difference but I think the nuggs that are closer to the light are much more dense.

damn i love your threads.i read alot of good info here! + repp

I'd give you +rep if I could, you got some coming your way again when it will let me.

Thank you for always pushing people to use their brains. You are definitely the man, keep it up and don't let people give you shit. You know a lot more technical facts about how everything works within our rules of physics to argue with.

desertrat said:

thanks, if you nail the temperature/light frequency questions in your balls to the wall thread then with this I think we've got most of the difference between indoor and outdoor grows covered.

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Ah just found this fine new thread you started. Subbed!

But.... I think there is one very important question that I have not seen adequately addressed regarding indoor v outdoor: Nutrient needs given the difference in light intensity. Specifically, optimal potassium levels for indoor v outdoor.

Someday, a scientifically minded grower will run an experiment on that *hint* *hint*

Nitegazer said:

Ah just found this fine new thread you started. Subbed!

But.... I think there is one very important question that I have not seen adequately addressed regarding indoor v outdoor: Nutrient needs given the difference in light intensity. Specifically, optimal potassium levels for indoor v outdoor.

Someday, a scientifically minded grower will run an experiment on that *hint* *hint*

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So much to do, so little time. I'm a great believer in wiki learning - my part in it is to keep the physics on target, I'll let people with a life sciences background handle the botany, and together we'll learn something. From what I can tell there is plenty of work to keep me busy just to straighten out the physics misinformation.

ColaFarmer said:

I'd give you +rep if I could, you got some coming your way again when it will let me.

Thank you for always pushing people to use their brains. You are definitely the man, keep it up and don't let people give you shit. You know a lot more technical facts about how everything works within our rules of physics to argue with.

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thanks, just having fun, trying to learn something in the process, and share the knowledge.

Desert: I want to see the math you promised on lumens/cu ft. where lumens, as a unit of measure of light flux on a spherical surface , derives to your new cu/ft measure. Are you just taking the volume of the sphere over a given distance or what? I'm not trying to bust your balls, just need to understand your train of thought.

patlpp said:

Desert: I want to see the math you promised on lumens/cu ft. where lumens, as a unit of measure of light flux on a spherical surface , derives to your new cu/ft measure. Are you just taking the volume of the sphere over a given distance or what? I'm not trying to bust your balls, just need to understand your train of thought.

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got a few other things going on right now that i need to figure out before refining formula, but basically what i did was take a one inch thick layer around the plant and added up the lumens each cubic inch would experience from indoor and outdoor light. the figures are going to change dramatically based on the input from my next post where i'm going to debunk the 7000 to 10000 lumens per square foot myth.

after examining the origins of the light distance chart i found a good bit of physics originally calculated by caligrower in 2004. i took his chart, verified the numbers for a 600 watt hps light, then updated it for newer bulbs and this is what you get:



caligrower had light intensities for mj acceptable up to 70,000 lumens per square foot, which based on my personal experience may be high for some strains. for my chart, i lowered the maximum amount of light to 50,000 lumens until i can verify a harder number to go with. notice that this chart squares with growing experience, ie that you can get an hps light to within a foot without the plant suffering from too much light.


this gives you something more like this for your grow:



so, in summary - there is nothing sacred about 7,000 to 10,000 lumens per square foot, it is maybe coincidentally the intensity of the sun in many places, but indoor grows routinely exceed these values by at least a multiple of 5.

you can use the chart above to set your lights by making sure you have them placed at the appropriate distances for the wattage and type of light you are using. for instance, the chart shows that you get excellent light intensity from a 23 watt cfl at two to three inches from the plant, again squaring with experience. on the other hand, the chart shows that a 68 watt cfl is useless at eight inches.

UR gonna have to find a way to make that chart bigger!! I can't read it. I tried ctl + to no avail



Much better !
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