Lets discuss finding the light distance and heat balance

aeviaanah

aeviaanah

Well-Known Member
I haven't seen much on this debate other then separated in discussion, correct me if I'm wrong. Many people say to put your light as close as you can without burning your plants, how hot is your grow area with your light 2" above foliage? A light distance 2" away may result in a grow area being 90- 100 degrees Fahrenheit. Marijuana grows best within 70 to 80 degrees Fahrenheit. You could raise the light by 3 or 4 inches thus decreasing the temperature by 5+- degrees. Even tho the plants aren't being burned, the temperature around the plant may be too high for optimal growth. On the other hand how much light are you losing? What has more of an affect on marijuana growth- light or temperature and how can we find a good balance? Increase temperature and increase light output or decrease temperature and decrease light output? Of course it depends on the light and equipment being used to lower room temperatures. Lets discuss this without factoring in air conditioners and look at it as a heat to light output comparison.
 
aeviaanah said:
I haven't seen much on this debate other then separated in discussion, correct me if I'm wrong. Many people say to put your light as close as you can without burning your plants, how hot is your grow area with your light 2" above foliage? A light distance 2" away may result in a grow area being 90- 100 degrees Fahrenheit. Marijuana grows best within 70 to 80 degrees Fahrenheit. You could raise the light by 3 or 4 inches thus decreasing the temperature by 5+- degrees. Even tho the plants aren't being burned, the temperature around the plant may be too high for optimal growth. On the other hand how much light are you losing? What has more of an affect on marijuana growth- light or temperature and how can we find a good balance? Increase temperature and increase light output or decrease temperature and decrease light output? Of course it depends on the light and equipment being used to lower room temperatures. Lets discuss this without factoring in air conditioners and look at it as a heat to light output comparison.
Click to expand...

Debate? Game on! J/K :wink:

If the ambient temperature under the canopy - and roots - is cool, you're lights are less likely to suffer heat stress above the canopy, but if you're seedling is placed in the sweet spot 2" from your bulb, the entire plant is probably going to cook. I suppose this is why a fan blowing over the small plants helps keep them cool - so that the heat energy is dispersed. Hope that makes sense.

I hear a lot of folks talk about the using the back of the hand test, but it's not a fail-safe method. I can touch the glass on my cool tubes, but the plants can't take the heat and UV produced @ 2".

A plant placed under HID lights for the first time, should be given twice the safe distance for the first few days so they become accustomed to the strong light, but there are no absolutes, and you basically have to experiment, until you find a safe distance.

.
 
And to me it all boils down to the max lumens you can safely get to the tops of the plant. There is such a thing as 'too close' I guess what I am saying is you push the limits at the tops of your plants. So the the lower growth gets the max penetration. Thats why sog and scrog works so well. With such an even canopy you can back the light off a bit still getting good lumens to the entire crop with a bit of cooler temps. Make sense?
 
cowboylogic said:
And to me it all boils down to the max lumens you can safely get to the tops of the plant. There is such a thing as 'too close' I guess what I am saying is you push the limits at the tops of your plants. So the the lower growth gets the max penetration. Thats why sog works so well. With such an even canopy you can back the light off a bit still getting good lumens to the entire crop with a bit of cooler temps. Make sense?
Click to expand...

I use scrog and am doing about 4 inches away from canopy, i lose about 2 - 3 degrees per inch. Its amazing how much light one loses over an inch of distance. Looking at the chart I am too close, the chart is in reference to the amount of light, not heat. I thought one couldnt get too much light? is 143,239 foot- candles too much? I am using a 400 watt HPS
 
aeviaanah said:
I use scrog and am doing about 5 inches away from canopy, i lose about 2 - 3 degrees per inch. Its amazing how much light one loses over an inch of distance. Looking at the chart I am too close, they must be using an 'In general' temperature.
Click to expand...
It is. You know the sun on a near perfect day is around 10,000 lumens a sqft. My thinking is with HID is getting around 16,000 or so to the tops is my max. Then even with a 3 or 4 ft plant the lower areas are still getting 5,000 or 6,000 give or take, 3,000 being my rock bottom. Temp issues are not as touching having the lights backed off a bit and it also lets you feed a bit stronger. Heavy nutes and close light can be a gamble. Just some thoughts.
 
[FONT=Arial, Helvetica, sans-serif]Candlepower is a rating of light output at the source, using English measurements.
Foot-candles are a measurement of light at an illuminated object.
Lumens are a metric equivalent to foot-candles in that they are measured at an object you want to illuminate.
Divide the number of lumens you have produced, or are capable of producing, by 12.57 and you get the candlepower equivalent of that light source.[/FONT]
 
temps are pretty much the only limiting factor.. and as for a 5 degree drop in temp from raising an inch, i dont think so.


mine stays a good eighteen in. away from tops with minimum ventilation.
400 hps w/o cool tube. (remote balast)
 
S0uthernSm0ke said:
temps are pretty much the only limiting factor.. and as for a 5 degree drop in temp from raising an inch, i dont think so.


mine stays a good eighteen in. away from tops with minimum ventilation.
400 hps w/o cool tube. (remote balast)
Click to expand...
18 inches with a 400 is nice. Even if you used a cooltube, IMO 14-16 inches is about as close as I would get.
 
Man, I can't believe the difference in technique from a 250hps to a 400. I am right on top, being only 7-8 inches off the tops with my 250hps, no cooltube, very good ventilation.
 
14- 16 in? You say that is a good ballpark range from the bottom of the light to the canopy? Thats only 8,000 foot candles as opposed to 90,000 (what im getting) how do you figure?
 
My bad. Mixed up lumens and footcandles for the suns output. I meant footcandles instead of lumens for the sun. So ya that is my preference. Feeding is more forgiving, less stress, but ya still get a nice yield. Its all good.
 
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