quick question?

[cash4hash]

How far/close should my400 hps light be to the tops of me plants ? any help welcome thnx. :)

[luckydan]

I would recomend that the 400 watt light should be no more than 10 cm or 6 inches away depending on the stage of growth eg.seedling or mature plant....
happy growing......

[luckydan]

you can get it within a couple of inches if you have a fan blowing at the light....

[Zandor]

Monitor the temperature at the top of your canopy that will tell you how close you can get your light with out hurting your plants.

[latewood]

but Z, what temp do you want to see? when monitoring canopy temps?

[turtle420]

I think a good test is the hand test...

Place your hand under the light, and move it closer until it starts burning... then place your plants just a little bit lower.

You should have air circulation over your 'canopy' and/or over your plants. You might consider a sealed reflector housing... or a cool tube.

[Zandor]

but Z, what temp do you want to see? when monitoring canopy temps?
To be safe no more then 85f at most. A better temperature is 78f but there are exceptions like if you are using CO² then you need hotter temperatures 85f-88f but not in vegetation cycle for vegetation cycle you should not rise above 83f even if you are using CO². If you are in flower cycle the first 30 days you should not go over 88f period. The last 3 weeks you can bump the temperature up as long as you are using CO² to as much as 90f. Just increase the water supply because they will drink it up very fast the warmer it is.

I wish there is one set temperature that is perfect for every plant and strain but there is not. Each cycle can use a little different environment conditions. The idea it to tweak the environment to match the cycle of the plant.

This is why I don't go deep into explanations. There are many expectations you should consider but for more then 90% of the members and other people growing it just confuses them.

Yes it's a hearty plant and can survive and grow in many different environments. Yield is as much a matter of opinion as is taste. Some are happy and feel successful if they finish one plant and yield 4 oz from it. Others want the same plant to yield pounds. It's a matter of environment control, growing technique and many other things that change an average yield from a few ounces to pounds.

Now have I confused everyone :)

[amckean]

I'm using a 400w HPS and I red in a grow book by Mel Frank that the light should be 18" to 24" in early stage of vegative growth and I have mine at 18" and they seem to be growing fin with no stretching but at 24" it seemed to slow down growth for a week until I lowered it again.
Hope this help
Ali

[Zandor]

I'm using a 400w HPS and I red in a grow book by Mel Frank that the light should be 18" to 24" in early stage of vegative growth and I have mine at 18" and they seem to be growing fin with no stretching but at 24" it seemed to slow down growth for a week until I lowered it again.
Hope this help
Ali
Mel (the ass hole) Frank wrote his book about 30 years ago and has sense disavowed everything he wrote. Most of his conclusions have been proven inaccurate anyway. You should pick up a newer book with better information.


There are two factors to consider. Temperature is first; monitor the temperature at the average height of your plants. To close and you burn the tips to far away and you give up luminance penetration (PAR). Second is Luminance loss. Most experts are in agreement that light intensity diminishes exponentially fast.

For example:
A 400-watt MH from 0â?� to 12â?� is about the same luminance say 55000
Same light at 24â?� the luminance is now about 30000

Still good

Same light at 36â?� the luminance is now about 1200

Fan leafs block most of the light so nothing below sees enough of the light of day to do any good.

About 16â?� is average if your plants get too tall just bend them over (if you bend them over the buds get more light and grow bigger). You could crop them to keep them short and bushy you crop between the 4th & 5th node early in the vegetation state for best results.

I hope this helps

[latewood]

Z how does that distance equate for a 1000w?

Z, If using a 1000w light, but keeping temps controlled in the low 70's, is there as much need for Co2 enhancment?, or do the cooler temps keep the Co2 levels from dissapating as quickly? Or am I totally off base, because I am under impression that heat caused by the 1000w ballasts/bulbs is the reason for the lack of Co2?

turtle...having 2 good fans, 1 to oscillate, the other toprovide airflow right across the top of the canopy, like you said, this works especially well if you have AC

[Zandor]

The lack of CO² is by the plants using it. Warmer temperatures make it easer for the plants to process the extra CO².

The only part light plays is you need to have HID lights, fluorescent lights don't have enough lumens for the plant to process the extra amount of CO².

You can get fresh CO² by changing out the air but you will only end up with normal amount around 300 PPM. Enhanced CO² is more like 1500 PPM extra so that raises the level to 1800 PPM to feed your plants.

So cool temperature is great but if you use enhanced CO² then you need to push the envelope and raise the temperature to around 85-88f or even into the low 90. Yes you run some risk of hermie but I have found the plants respond to enhanced CO² and do not turn hermie. It takes temperatures over 100 for extended periods to do that. It's all about the environment they live in. You can push the limit but being in control is the key.

[Zandor]

The math formula for light calculations. You can do the math your self and see it's different for each light wattage and bulb type. The only thing that is the same is 0-12" the lumens are the same you start with. From 12" to ? is how fast you loose the lumens and it's different from wattage to wattage.

I=L/D²

Light output divided by the distance squared FYI.

[Trichome Creator]

If it's to hot for your hand at the top of the canopy then it's to hot for your plants. 75ºF is the optimal tempature for cannabis. If you use CO2 then your plants can endure tempatures up to 90ºF for short durations of time if your CO2 is dispersed at 1500 ppm. Hope this was of help to you.

[BOYZNUS]

I FOUND OUT THE HARD WAY,,, WHEN YOUR LIGHT BRACKET BREAKS,,,, YOUR LIGHT FALLS ON YOUR PLANTS,,, AND YOU HAVE TO CUT OFF 6 OF THE BUD TIPS. BURNT TO SHIT. I HOPE SHE SURVIVES OK. WILL POST A PIC TOMORROW

[JohnnyPotGrower]

cash4hash,

i am growing with a 400W HPS and my seedling started about 24" away from the light and i saw great growth despite the distance. it has since grown and is now only about 12" from the light and its starting to get to the point where i may have to raise the light. What I would recomend (if you are still taking suggestions) is to leave your young seedling a good distance away (at least 18-24") from the light b/c while young it is suceptable to being burned if too close. It will still grow just as well (at least mine did). Then, if you really want to get it as close as possible, I would lower the light to 12" from the top once you have at least the 2nd-3rd set of leaves. You really dont need to, as i have seen in my grow, but i think the closest it should be is 12" and the furthest 24".

Hopes that advice helps.

-JPG

[Zandor]

If it's to hot for your hand at the top of the canopy then it's to hot for your plants. 75ºF is the optimal tempature for cannabis. If you use CO2 then your plants can endure tempatures up to 90ºF for short durations of time if your CO2 is dispersed at 1500 ppm. Hope this was of help to you.
Well that's not really a good indicator. Normal body temperature is around 98.6f. So for the heat to be felt you need to build up temperature above 90f and that is to hot for plants. A good remote temperature probe is a better way to know the temperature. You check it when the door closed and the room up to normal operating temperature. You can't do that with the door open and you standing there with your hand out. The room cools and the temperature changes.
You need to know real world temperature.

[Sentinel]

so would a thermometer placed at the top of the canopy give you an accurate temp.?

[Zandor]

Well a wireless version that monitors temperature and Humidity is what you really want. But you can use one of the remote indoor / outdoor ones that have a wire to a remote probe.

Like this FAQ

http://boards.cannabis.com/showthread.php?t=40868