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What distance should my light be from my plants?

dirtracer

New Member
Does that apply to 300w LED? heard different things. Also, can I trim 2-3 large fan leaves up top that are blocking light?
Sorry if i misposted...
For (artificial) light, there is a law that always applies known as the Inverse Square Law. It states that light diminishes exponentially in energy as the distance is increased from the source.

A good example is that you might be getting 1000 PAR Watts at 4" from your light source, but that would change to 250 PAR Watts at double the distance (8"). This law makes it EXTREMELY important for indoor plant growers to get their light source as close as possible to their plants. The amount of light your plant receives is directly related to it's yield/flower density.

The problem: Indoor lamps used for plant cultivation (HID - High Intensity Discharge) give off large amounts of heat, to such a degree that they could cause damage to the plant if put too close.

Indoors, there is an optimum distance/height between the plants and the light source. This distance fully illuminates the whole canopy with direct light from the source, but is as close as possible to the plants for maximum lumen intensity. This will be called the OLH, for Optimum Lamp Height.

Ultimately, to get the best light efficiency from your lamp, you want it at the OLH at all costs. But how can you get it there without causing harm to your plants with the abundant heat?

First, try moving your light to the OLH and see what it does to your plants. If they have no problem, then you're fine. If you have a high output HID, this probably won't be enough.

Next, try actively exhausting your light hood by hooking up a direct exhaust system to the hood, and then move your lamp to the OLH and see if the plants are O.K. If the plants still seemed affected by the heat, then you must add glass to your actively exhausted lamp hood. Glass will absorb/reflect/filter some of the light energy being emitted by the lamp.

The number would seem relatively low, around 2-3% of PAR wattage, but it will effectively filter out almost all of what little UV-B is emmitted by the lamp. UV-B is believed, and has been shown, to have a positive influence on the potency of Cannabis.

Overall, it would be beneficial for one to add glass if needed to keep their lamp at the OLH, due to the all-powerful Inverse Square Law; moving light farther away will greatly reduce the amount of energy being emitted and is reaching your plants (Light intensity is directly related to yield and flower density).

Almost all glass offered today for insertion in air-cooled lamp hoods is tempered glass, which is regular glass with low amounts of impurities. If one was looking for the most efficient glass for their hood, quartz glass will allow the transmission of UV-B, but is not made specifically for light hoods.

And also remember, that if you have a rectangular garden, it is important to position the longest side of the reflector parallel to the shortest side of your garden. (from FAQ by Head Rush)

Additional note: you should periodically inspect and clean your light hood and bulbs, especially after foliar feeding or underleaf spraying for insects. The dust and dirt that collects will definitely decrease reflectivity. Isopropanol alcohol, glass cleaner or water (and a soft cloth) can all be used to remove streaks, dust and spots.

Contributed by: MedMan

There are a number of factors which play a part in the temperature radiated from your bulb, watts, hood design and air circulation for example.

A simple method of testing for temperature is to use the back of your hand; if its too hot for your hand, its too hot for your plants. Good ventilation is the key to getting your light closer to the garden.

Editor's note:

Recommended typical OLH distances:

Flourescentsroximimty
400w HPS: 1 foot
600w HPS: 1.5 foot
1000w HPS: 2 foot

Author: BobbyDigital
 

G13haze420

New Member
:thanks:I thought marijuana was supposed to destroy brain cells, after reading this, I doubt that it is true.:smokin:
yo dude they leaked the truth about the tests gov did and marijuana
they put a gas mask on a monkey for 5 minutes straight with stright thc and no air and we all no if your brain doesnt recieve air for 4mins you lookse braincells so for a 1min everyday for however long they did thee tests for the monkeys were loosing brainscell DUE TO LACK OF OXYGEN NOT THE THC FOR FUCKSAKES ITS THE CURE FOR CANCER......FUCK OFF GOVERNMENT!
 

purzurples

New Member
Yea Vapor that is just a rule of thumb, Air cooled will allow you to get much closer. Best bet would be just to hang a thermo guage at the distance you want the light at and measure it from that. I can keep my 600hps at about 12in and I dont even have a air cooled hood. You should be able to get to 12 or 10 I would say at least. well GL broham.
"Thermo gauge" <- do you mean "Thermometer"?

I doubt you can put a 600watt HPS 12inches from ANYTHING and not burn the shit out of it, lol.
 

DeerHunter33

On Vacation
:420:
for (artificial) light, there is a law that always applies known as the inverse square law. It states that light diminishes exponentially in energy as the distance is increased from the source.

A good example is that you might be getting 1000 par watts at 4" from your light source, but that would change to 250 par watts at double the distance (8"). This law makes it extremely important for indoor plant growers to get their light source as close as possible to their plants. The amount of light your plant receives is directly related to it's yield/flower density.

The problem: Indoor lamps used for plant cultivation (hid - high intensity discharge) give off large amounts of heat, to such a degree that they could cause damage to the plant if put too close.

Indoors, there is an optimum distance/height between the plants and the light source. This distance fully illuminates the whole canopy with direct light from the source, but is as close as possible to the plants for maximum lumen intensity. This will be called the olh, for optimum lamp height.

Ultimately, to get the best light efficiency from your lamp, you want it at the olh at all costs. But how can you get it there without causing harm to your plants with the abundant heat?

First, try moving your light to the olh and see what it does to your plants. If they have no problem, then you're fine. If you have a high output hid, this probably won't be enough.

Next, try actively exhausting your light hood by hooking up a direct exhaust system to the hood, and then move your lamp to the olh and see if the plants are o.k. If the plants still seemed affected by the heat, then you must add glass to your actively exhausted lamp hood. Glass will absorb/reflect/filter some of the light energy being emitted by the lamp.

The number would seem relatively low, around 2-3% of par wattage, but it will effectively filter out almost all of what little uv-b is emmitted by the lamp. Uv-b is believed, and has been shown, to have a positive influence on the potency of cannabis.

Overall, it would be beneficial for one to add glass if needed to keep their lamp at the olh, due to the all-powerful inverse square law; moving light farther away will greatly reduce the amount of energy being emitted and is reaching your plants (light intensity is directly related to yield and flower density).

Almost all glass offered today for insertion in air-cooled lamp hoods is tempered glass, which is regular glass with low amounts of impurities. If one was looking for the most efficient glass for their hood, quartz glass will allow the transmission of uv-b, but is not made specifically for light hoods.

And also remember, that if you have a rectangular garden, it is important to position the longest side of the reflector parallel to the shortest side of your garden. (from faq by head rush)

additional note: You should periodically inspect and clean your light hood and bulbs, especially after foliar feeding or underleaf spraying for insects. The dust and dirt that collects will definitely decrease reflectivity. Isopropanol alcohol, glass cleaner or water (and a soft cloth) can all be used to remove streaks, dust and spots.

Contributed by: Medman

there are a number of factors which play a part in the temperature radiated from your bulb, watts, hood design and air circulation for example.

A simple method of testing for temperature is to use the back of your hand; if its too hot for your hand, its too hot for your plants. Good ventilation is the key to getting your light closer to the garden.

Editor's note:

Recommended typical olh distances:

Flourescentsroximimty
400w hps: 1 foot
600w hps: 1.5 foot
1000w hps: 2 foot

author: Bobbydigital
 

DeerHunter33

On Vacation
have new hps bulbs, HORTIFLUX.. SM SHIT 85.00 A BULB, LEYS C IF IT MATTERS.:thanks:
 

Siscokid

Member of the Month: Feb 2012
OK, so no matter HPS, MH it's all about getting it as close to the plants without burning the top of the hand when testing... I'll get right on it and see what happens.:thumb::420:
 

Spicy2na

New Member
I'm trying to figure this out myself. I'm currently running a 400W HPS/MH Cool Tube with a 165CFM Fan doubling as my tent ventilation. Trying the hand technique, I can touch the tube with my hand and it's only warm. Does this mean I can put my girls that close?
 

Siscokid

Member of the Month: Feb 2012
You may not want to put the plants right on the tube..stay at least 6-9" from the "sweet spot" and if you drop the light an inch every 1-2 days without seeing any stress on the girls you could play with it till you are satisfied. Just my opinion.
 

Spicy2na

New Member
Right on Sis. I'll take that into consideration. Problem is that the really seem to love it a lot more when they are almost touching the glass. I think my girls are just really being considerate and making sure the glass gets massaged.
 

Spicy2na

New Member
what would be a decent height for LED lights to be above the plant in flowering?
I have 2 x 240W flower LED's and am struggling with the optimal height to be using them at.
You wouldn't be struggling using metal halide! Isn't everyone saying the LEDs are not the way to go? I'd say put those things as close as possible! But then again I know nothing about LEDs. Good flashlights!
 

highteck

New Member
You wouldn't be struggling using metal halide! Isn't everyone saying the LEDs are not the way to go? I'd say put those things as close as possible! But then again I know nothing about LEDs. Good flashlights!
Yadda yadda HID lamp yadda yadda k, I asked about LED's not HID, I know all about HID lamps, The fact that you have even gone ahead and started saying LED's are no good shows you obviously have no valuable information based on the question I asked. So your input was not so much as needed as one that would of contained valuable well based knowledge and experience . thanks for the reply but it didn't give me any information that I didn't already know. :bravo:
 

Spicy2na

New Member
Not sure where I said that LEDs were junk? I said I know nothing about them. Tone the testosterone down a little champ. We all here are In this together.
 

highteck

New Member
No testosterone in this thread at all, I was simply stating the obvious, No you did not say they were junk, But you did rebroadcast some hear say "Isn't everyone saying the LEDs are not the way to go? " I'm sure if you browse threw this forum enough you will see that LED's are not only the way to go but that they work just as good as some of the HID lamps also on this forum, So before you go flaming, just check into things before speaking about them and come up with your 'own' view. thanks for the reply :Namaste:
 

TBayChronic

New Member
Anyone kno how close you can keep the aerogarden lights hood?
 

TBayChronic

New Member
The AeroGarden uses full-spectrum compact fluorescent bulbs exclusively designed for the optimal amount and type of light needed for robust, healthy plant growth.

# Light output in Lumens: 1450
# Energy used in Watts: 26
115 Vac
60 Hz
26 watts

thats the info i got on the lights i just bought it, its on its way in the mail its this model AeroGarden | AeroGarden Extra Elite Indoor Garden, Seed Kit, Grow Light

It has 3 delux grow lights.... delux grow lights might be abit better then the info i got there because most info you can find is on older models and mines supose to have more light then the older ones... i dunno if thats better lights or just more of the same lights *shrugs* ..... the site doesnt give much info but lets say 3 lights with the info up top



Edit: I checked it out some more n the aerogarden a size down (the aerogarden 7) uses 2 grow lights which I think go with the info above... Mine has 3 "delux" grow lights but the site gives no info on either... The info above is what someone posted online saying that's what it says on the lights packaging when you get them, but again I think that's for the aerogarden 7 grow light not the delux grow lights
 

Excited2start

New Member
I wouldn't know for that thing. I know in general CFLs work best 2-3 inches from the plant to allow for penetration of the lower parts of the plant. hope this helps. if it has an adjustable light then I would try it at different heights to find what works best for you needs.
 

TBayChronic

New Member
Ya I was thinkin 2 inches should be good... If u watch the video through the aero grow site link I posted it looks like they have it 2-3 inches but when it's sprouting they have it right high... Do you kno why? n what you'd recommend for marijuana
 

TorturedSoul

Member of the Month: May 2009, Oct 2010, Sept 2017
For 26-watt CFLs? An inch above established plants, with a fan placed so as to carry away the heat that they produce (yes, CFLs produce heat; for the wattage/light-output, quite a bit, lol).
 
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