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Scientific lighting question !!

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OK ive got a question for all the experienced growers out there that will put the whole "how much light" thing into perspective for me, ive such a simple mind.. :rolleyes:


OK, THEORETICALLY, under ideal and identical conditions, if u had like 6 identical plants say on there fifth leaves and ready to veg, and put them in seperate rooms under the following lights, no topping etc, how long and what yeild would you expect to get off each.... with me ppl ?? lol


1 . Under a 48w CF

2 . Under like 200w of Fluro lights

3. Under a 250w HPS

4. Under a 400w HPS

5. Under a 600w HPS

6. Under a 1000w HPS


Ok now for the ppl still following even though you "could" grow from start to finish under all the above, what would the time/yield differences be?


Sorry for my blabbering .... you know how it gets lol :smoke



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im all new to indoor growing but what i can say for certain is that the hps will perform way better than any fluro from vegetative to flowering cycles...


the stronger the light, the chances are your yield will be increased BUT too much of a good thing as well all know can be really bad....


take my setup for example...im running a 400watt hps in a wardrobe with 2 fans and 3 plants....all of which are kicking along quite nicely thanks to the follow stoners here but if left unchecked, my setup is a plant killer....now if i were to have a 600watt hps going in the same space, my plants would be dead due to excess heat although it is possible to run a 600 with great ventilation....


also a 1000watt globe can really burn babies, can even bleach plants if left unchecked....so i would recommend going with a lower watt globe if possible depending on what kind of grow u wanna do and where it is going to be grown....if i had the choice now, i would probably have got a 250 for my setup...

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Yeah, yeild is to a large degree determined by light, certainly, but growing is a holistic exercise, and you need to have everything in good order to get a yeild. Then you've got to take into account the genes, which accounts for a very, very large part of determining what your yeild will be, lighting completely aside. You'll never yeild well with a shitty bagseed equatorial sativa in a room with 48w, as it's totally unsuited to the conditions, but a short temperate indica, with a 400w system and you could be harvesting anything from 4-12 ounces. Maybe a pound or in some exceptional circumstances 2 from a 600w. But that's the thing, it's not just "all about lights."


Hope that helps, and doesn't just make things more complicated.


To really test effectiveness of the lamps, you'd have to use identical clones from many plants, all grown under as similar circumstances as possible, with lighting being the only variable. You'd also have to try and even out the temps, and compensate nutrient requirements of the plants from different areas.


Still, it would be a worthy excercise, just don't know many people with the space to make that many grooms.


I'd say for the home cultivator though, a 400w light should give you all the lighting you need to harvest a decent crop 3 times a year, and have more than enough smoko for yourself with a good strain. :P Season to season your yeilds may change, but once you've hit a good formula for growing, try and stick to it. Use your own reasoning to determine whether information given to you is fact or fiction, and then apply or disregard the information accordingly. :P

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OK, THEORETICALLY, under ideal and identical conditions


Ok if the conditions are ideal and identical and you have a good strain.

then for me

my 400 nets me normally about 8 to 10 ozs,

my 600 gives me about 12 -18 ozs.

I get these higher yeilds because I grow the plants bigger, but you could increase the amount of bud per year by only growing small plants and harvesting more often.

your spot on thinking Light = Yeild.


i recently just had two crops almost die on me and I got buggar all buds of the plant maybe 2 to 3 ozs maximum.

the first time the grow stuffed up was because I switched from H202 to Bio bugs and my drains got blocked so that my top box held water and I got root rot.

The second one was mainly my own fault, I decided to keep a male in coco and in the same light as my plants.

ALl that gave me was insects my first battle was spidermite, but neem took care of them pretty quickly.

then the bitch got fungas gnat in advanced stages, ( i didnt notice them until I saw flies coming out of my clayballs)



fluros well I never managed to get much more than about 2 to 3 ozs per plant.


::P: :thumbsup

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cool thanks ppl, youve all been a big help yet again.


Ive got myself a 600w and hoping to veg prob 2 plants to a descent size before switching to flower.


Im worried about the 600waters heat, i originaly wanted a swaller one but its what i was given so who am i to argue :P


How much venting would be required for a light of this size?.... or is it a case of just keep adding fans till the temps are right?


Thanks all



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Your best bet is to get a 8 or 10 inch exhaust fan mounted to the roof.Then add a Y junction to it that has a 8/10 side to attach to fan and the other two are 6" which you add 6" duct to one and run that to the moguel/ light fixture this will remove most of the heat and you still have the other 6" duct hole to take the heat from top of the room or run duct into the canopy level if needed.. You might not even need inlet fans if it sucks enough out.. All you should need is a passive inlet vent and a oscilating fan inside..

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Exacly what i was thinking... thanks for all yor all along the way stonedas...


..another quick question, what should the tempreture be sitting at if i measured it just at the top of the plant?... at its top leaves?


Just alittle worried about burning the plants now....



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Ideally, about 25-28, but you can certainly grow plants well in temps up to 32 or so provided they're being given enough moisture and the other necessities of life to survive. Above 32 and your plants will shut down in growth, and be just trying to survive.


Take temps from directly underneath a leaf, either by positioning a sensor from an IN/OUT hygro/thermo unit, or by hanging the thermometer inside the canopy. If you allow direct light to hit it from the lamps then it will read high, you're after the temps of the air around the leaves. :P


An oscillation fan, say 23cm, would do you a great help too. :P

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G'day bro,


have never used fluro, so I can not comment on those. But I can comment on using HPS to flore.


The first part of your question was about the yeild using a HPS light at different wattages.


If your room is fully dialed in and the only thing different is your light then as far as yeild go's you should be able to achieve to following


average yeild = 1 gram per watt in flore room

good yeild = 2 gram per watt in flore room

expert yeild = 3+ gram per watt in flore room


But as I said, you MUST have the room fully dialed to achieve good results. Light is only one factor of many.


As far as how long it takes to finish flore ligths do make a differance. ie. lets say you had a grow in flore under 2 hps lights, usually under those lights it would take about 8 weeks to flore. But if you took one of the hps away and added a MH instead, your grow would most likly another week or two, until flore is finished.


Sometimes this can be very advantages if you are growing big tree type of grow and want huge buds.


Another factor affecting the speed of the flore is stress. The more a plant is stressed the faster it will flower, but the payment will be a lower yeild.


Stress can come from so many different things in a grow room. ie wrong humidity, wrong room temp, wrong res temp, wrong use of nutes, wrong airflow, wrong co2, wrong lighting, ....the list gos on and on.


Stress not only affects yeild but also affects quality and THC production. The more stress the lower the yeild and quailty.


The only way to remove stress is by having your room fully dialed in. This is where experiance comes to play (and a willingness to experiment).





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