Most common and easy fix to massively increase yield. Plus dispell a myth

Japanfreak said:

This is from cannastats

Distance and the Sweet Spot
Every top-lit indoor garden using artificial HID lighting has a sweet spot located directly under the lamp, where it's closest to the canopy. If not accounted for in your plans to distribute available light, fc in the sweet spot can far exceed that of the sun, especially when lamp cooling technologies are used to reduce normal distances limited by heat. Finding the limits of your coverage area implies a compromise between the minimum light levels at the outside edges of your area (furthest from the lamp) and the maximum light level at the sweet spot (closest safe-point to the lamp). The happy medium is not to overdose the sweet spot with too much light (or heat) and to distribute enough light to the outside edges of your grow space for acceptable growth. The controlling factor for both of these limits is the height of the lamp above the canopy. Reflective surfaces surrounding your garden will help reduce light losses at the outside edges, but light at and below the sweet spot is controlled by distance between it and the lamp. The table below gives an idea of the distances involved, fixtures used during the meter readings are common to indoor gardens.

Approximate fc in the sweet spot
(metered directly beneath the bulb)​

Lamp Distance Foot-Candles 1000 watt HPS 1.50 foot (18 inches/45 cm) 9,000 fc 600 watt HPS 1.00 foot (12 inches/30 cm) 9,000 fc 1.50 foot (18 inches/45 cm) 5,600 fc 400 watt HPS 0.75 foot (9 inches/23 cm) 9,000 fc 1.50 foot (18 inches/45 cm) 4,000 fc 250 watt HPS 0.58 foot (7 inches/18 cm) 9,000 fc 1.50 foot (18 inches/45 cm) 2,800 fc

Highlighted items approximate the closest distance that particular lamp should be to the sweet spot to avoid over-lighting. (those interested in photosynthetic radiation can use this PPF PAR converter.)​

The highlights don't convert it looks like but the first number is the closet you should get a bulb and that's under good environmental conditions, along with heat I bet a lot of people have to keep them higher.


I know a lot of people think a cool tube is made to keep their lights within 2 inches of their canopies but In my experience, the best place for my bulbs is a wee bit higher than most people would think in my gardens.
​

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The reason I believe in 2.5+ feet is through personal experiences and advice. The above calculations are just to simple. It doesn't give ambient heat temperatures and radiant heat fluctuations so if someone is growing in an 85 degree room would it still be okay to have the 1000 wt 1.5 feet away or would it be more advisable to have the light further away to lessen radiant+ambient heat stress on the canopy? what kind of lid?

Cool tubes are made primarily for Co2 inclosed operations and to keep rooms a little cooler by not using a metal lid which raises room temps. Plus there's only so much a plant can absorb. Why have a cool tube inches away sacrificing light spread.

TaoWolf said:

In addition to heat, there is the light footprint to take into account if using a reflector/hood... and if the fixture is too low the outer plants/foliage won't get direct light... But what scientific proof are you referring to (can you cite/share it)?

Otherwise, commercial grow operations have the space to use the maximum area/footprint of a light over the maximum number of plants for efficiency - most individual growers are more concerned with getting the most they can from a light in a restricted area with a limited number of plants. Just different situations.

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It's not just maximum area/foot print. If an individual grower is growing a 600 watt over a 4x4 foot area it still applies. Why move your lights that close when you'll be sacrificing out side or in some cases causing heat stress to inside colas. How many grows have the largest buds grown on the outside perimeter of the area, many. This means that the light and temps are better on the outside and too hot on the inside and if you move that light up you'll be getting larger colas in the middle.

skunky33 said:

The reason I believe in 2.5+ feet is through personal experiences and advice. The above calculations are just to simple. It doesn't give ambient heat temperatures and radiant heat fluctuations so if someone is growing in an 85 degree room would it still be okay to have the 1000 wt 1.5 feet away or would it be more advisable to have the light further away to lessen radiant+ambient heat stress on the canopy? what kind of lid?

Cool tubes are made primarily for Co2 inclosed operations and to keep rooms a little cooler by not using a metal lid which raises room temps. Plus there's only so much a plant can absorb. Why have a cool tube inches away sacrificing light spread.

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I do not have an option of making use of the potential light spread regardless what i'd like so it makes no difference, for me, if temps are fine then closer is better and as such so is yield.

Medi 1 said:

ya im way closer than 2 foot. i run at 8 inches or so. no heat issues if you have the right venting set up. all going to depend hpow you want to use it realy...futher away weeker lumens but bigger footprint. closer less footprint but more intense lumens. i go close to use less plants and food and time but yet get same bud as i use the light more efficiently.

so the way i run it cost me less but get same end result and tighter budz and better use of the foods

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Are you sure your getting the best results though. Maybe you are. I get a reading 7500 candle feet 1.5 feet away and 6800 candle feet at 3 feet away using a spreader and have a 5x5 ft area so all plants are getting and or exceeding recommended ft candles at 2.5 feet away from center in a concave scrog.

skunky33 said:

It's not just maximum area/foot print. If an individual grower is growing a 600 watt over a 4x4 foot area it still applies. Why move your lights that close when you'll be sacrificing out side or in some cases causing heat stress to inside colas. How many grows have the largest buds grown on the outside perimeter of the area, many. This means that the light and temps are better on the outside and too hot on the inside and if you move that light up you'll be getting larger colas in the middle.

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I can only speak for myself, but I have a 600w inside of a 2'x4' tent. I just don't need to cover a 4'x4' area so there's no loss and only gain (in PAR) by moving it closer to the plants than for what I'd need to cover 4'x4' - as long as I'm covering the 2'x4' with the footprint, why would I want it higher as long as they aren't being burned by heat?

tip top toker said:

So now you need to show proof that even if it were closer, and the temps hadn't altered, that he would have grown smaller colas. You are doing nothing but explaining in a peculiar manner the well know idea of putting your hand above the colas to make sure it's not too hot, little more

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All I know is that what I have seen and done. When you put a light too close it makes the plant warmer which can stunt growth in the buds. All the foot candle charts and light charts always say "This is a reference to the amount of light, not heat" So when looking at the chart you cannot simply just put it 8 in away without putting into consideration the heat thrown out by that light.

ya i feel i am getting the best i can. and you keep reffering to heat being close..so buy as better fan

mrdrywall said:

ive just recently added my 3rd 1000w hps to the grow room.a magnum xxxl (bad ass by the way) i did have a little bleaching of the tip of the colas a foot or so away from the lights. when i revamped the room adding my 3rd light i decided to go 2 foot away the coverage is out of this world.have 30 girls under them and all recieve great light to the eye but my concern is stretching , bein that far away.also my lights never get so hot u cant touch em. i have a 6 inch cent.fan cooling all 3.

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2 feet away is absolutely fine they're getting huge amounts of lumens so stretching shouldn't be a problem unless the strain is just naturally stretchy. ft candles at 24 inches is 11,400 you won't notice a difference between 64,000 ft candles and 6400 ft candles in growth. Under 5000 is when you notice a difference and that's at 36 inches without a spreader.

It's just a balance you have to find, one of the many aspects that make growers unique amongst each other. The balance is between establishing a substantial footprint without getting the light too far away, but the primary concern (for me) is footprint first. I use 3x3 screens and the footprint covers it just right with the 600 a comfy 2-2.5 ft away. Super buds. I COULD lower it and still "catch" the outsides of the screens but I've found that a balanced screen produces better than one with a sweet spot.

skunky33 said:

All I know is that what I have seen and done. When you put a light too close it makes the plant warmer which can stunt growth in the buds. All the foot candle charts and light charts always say "This is a reference to the amount of light, not heat" So when looking at the chart you cannot simply just put it 8 in away without putting into consideration the heat thrown out by that light.

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I have not even looked at the chart. This whole thread is about nothing more than not putting your light too close to cause heat stress/damage, little more.

If i put my light closer, i get better buds. That's all i've seen. I don't know what's being debated here?

Japanfreak said:

Holy shit dude I just got banned from Icmag over this issue. Some punk there was pulling out nasa research papers and talking about photons and telling people to put their lights within inches. Some people just won't hear it.

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Is there any forum that you haven't been banned from recently?

tip top toker said:

I do not have an option of making use of the potential light spread regardless what i'd like so it makes no difference, for me, if temps are fine then closer is better and as such so is yield.

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I understand. But you could be giving the plants 65,000 ft candles or 6500 it doesn't make a difference in terms of growth. What does make a difference is radiant heat that sucks moisture out of a plant even though the ambient temp is 78

And my plants still grow a lot better with the light about 8" away, certainly not "at least 2 feet away". What am i missing.

My lights are in cool tubes (not for co2 reasons, or just for keeping the room cooler) and if I didn't have cool tubes I would not be able to grow in the space I have. There is a whole variety of reasons why you may want to use cool tubes, style of growing is a Major one that comes to mind (i.e Vertical growing is impossible IMO without cool tubes)
If I placed my lights that far away (2-3feet) I would actually need to put them outside the cab...don't think my plants would be that happy with that...they would be a lot cooler though!! haha. Anyway, I run my plants to around 3-4 inches from my cool tubes. Of course heat causes problems, but as TTT said, if your hand can handle it, the plants can handle it. But each to there own I guess.

I have an aircooled 1000w on a mover and I keep the canopy about 12 inches at most. Sometimes the colas get a little closer. I've experimented different heights and I've got it about right where it produces well without any stunting or bleaching.

Medi 1 said:

ya 6 inch isnt enough to run 3 1k lights. i use a 6 inch on 2 600 here and its just right.

this other guys colas may have looked big but i bet was fluffy buds.

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six inch is plenty to cool those hoods the last one is a little warmer but by no means hot

obvious our ideas od control are diff is all. also depends on room size but id bet your fan runs full speed to cool it.

tip top toker said:

I have not even looked at the chart. This whole thread is about nothing more than not putting your light too close to cause heat stress/damage, little more.

If i put my light closer, i get better buds. That's all i've seen. I don't know what's being debated here?

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I don't know how big the light you're using is. The debate is whether putting a light closer is better than putting it farther in regards to yield. So there are hundereds of pictures showing lights 2.5 feet away producing 1 gram + per watt and not much difference in size and yield when grown closer.Plus give me proof that you know you're buds are larger than they would be if your light was 1 foot farther away. If scientifically there is no difference between 64,000 candle feet and 6,400 candle feet in terms of growth than why should I believe you. I began this thread because of the over emphasis on lumens when you're using a high wattage HID when it's not going to make a scratch of difference if your 1 foot away or 2.5 feet away except you might screw your plants if it's too close. Plus, you're saying that there's some loss in bud quality when lights are farther than a foot which is total and complete BS. You're basically saying that all bud in Amdam is of low quality since it's grown 2+ feet away from the light. You just want to be disagreeable

mrdrywall said:

six inch is plenty to cool those hoods the last one is a little warmer but by no means hot

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Yeah I used to run 2-1000 watters with one 6" just sucking out the hole in one end of the glassed in lids, it worked surprisingly well.

skunky33 said:

I understand. But you could be giving the plants 65,000 ft candles or 6500 it doesn't make a difference in terms of growth. What does make a difference is radiant heat that sucks moisture out of a plant even though the ambient temp is 78

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A majority of light is going to be blocked from lower foliage though - it would require a *significantly* higher amount of PAR hitting the top of the plant to maintain the minimum level of light required for full growth on leaves that are at the base of the plant. Optimally, even the lowest, most internal leaf would be receiving enough light to reach it's full production potential for the plant. One can't say any specific number of a certain measurement of light is adequate and that's all there is to it in the real world.

For example, there would be a huge difference between what would be required to adequately provide for a 4' tall bushy indica as opposed to a young 1' stretchy sativa. The needed PAR increases at an exponential rate with height/distance and according to how much foliage has to be penetrated. Unless you love a lot of popcorn bud, or only grow short, single-cola SoG plants, you'll have to go well above the minimum required PAR at the canopy to make all those other branches and leaves below the top layer get something adequate as well.

Otherwise, I'd ditch the 600w HPS and just use my 150w - I can cover the same 2'x4' area with enough light for minimal growth... but everyone knows (I hope) that a 600w is going to provide far more PAR to more of the plant and that equals more to harvest at the end of flowering...

With an air-cooled hood, my 600w is cooler at the same distance than my 150w as well. So I'm just not following the argument besides 'you could burn your plants if you get the light too close'...