a few questions about lights.

Im planning my next grow, but have only grown with cfl's before, so i have a few questions regarding HID lighting. Im growing in a 70 x70 x 100 cm tall box that is currently under construction. Will a 400w hps without a cooltube be too hot? I was planning to place 2 pc fans at the top for exhaust and 2 at the bottom for intake. Will this be enoough to deal with a 400 w in that space? i know that for a 400w you need a contact timer, will i still need one if i opt for a 250w?

How many plants could thisarea handle? Im aiming for 2-3 with a scrog, but im not sure.

Thanks

Bump, no replys?

ur measurements in cm or inches

Cm, as said in the origional post.

So your grow is about 3x3x4ft? That's pretty small. A 400W would be too much man. I have a 250W in an area larger than that and it's perfect. 400W would get super hot in such a small area without a cooltube. Go smaller light or go bigger grow area with better ventilation.

ya i missed the cm but ya thats seems pretty small

My space is almost identical to yours and I am vegging in there now with a 400w MH, and will flower with a 400w HPS, eventually (this is my first grow) I will flower in the upper half and veg mother clone in the lower half.

wht 100CM about 3 feet? that is half as high as mine so you will be limited to one chamber.

You can do it but you will have to move alot of air to keep the light and temps down.

*edit Those PC fans will not cut it.

Also Suck don't blow.

Suck the air out of your room don't blow air into it, all your air in can be don passively

Temps depend on your ambient temp.
400W without a cooltube is too hot to handle if you only plan on using 2 PC fans. Even if its below frost level most of the time.

Running a 400W without aircooling it makes you use it at a way higher level above the canopy which translates to much less effective lumens.
You will be better off running a 250W way closer.

If you can't get an aircooled reflector go with the 250W.

You want AT LEAST 80cfm on you exhaust vent. I use that much on my 30X50X120cm closet and it fits just right in there creating a gental breeze for the plants to dance with.


As for how many plants to fit - its mainly a question of time. more plants = less veg time needed.
If you can its easier to handle a 1 plants SCROG, but you'll need to veg for about 2 months under proper circumstances.
Anyhow, make sure you can access all the plants.

Use pots big enough to cover as much of the floor as possible.

McFonz said:

Temps depend on your ambient temp.
400W without a cooltube is too hot to handle if you only plan on using 2 PC fans.
You want AT LEAST 80cfm on you exhaust vent.

Click to expand...

Ok I agree with you but would like to add something. Do not cool you light/s with the air from inside your grow room, and do not vent your light heat to the area where your intake air for your room is coming from. If you vent and intake your Hood to/from outside or the attic you will not be using your AC to cool your lights and your Air to ventelate the room is not warmed up by the light. you can also get by with a much smaller fan to vent your room, like a PC fan maybe.

I use a Sun Systems Air cooled hood and a 160 CFM fan to cool it, the glass is warm to the touch and the rest of the hood is room temp.

*edit My cabinet is 2 x 2 x 6 (thats feet for you euros) inside a closet and i run a 400w MH for veg.

I cool the lights with air from my grow room - one less vent. I just use a powerfull one to do so.
If you want to heat up the room you could use the air from the hood to circulate back to the bottom of the plants to heat them up.

Well the 250w is looking much more practical, also considering supplementing with some 6400k cfl's during veg and switch to 2700k during flower. Will 2x 57 cfm fans as exhaust keep this cool enough? Or is one enough for a 250w?

Are you going to use a hood? What kind? How will you cool it? Have you considered MH light for veg and an HPS for flower?

What is the climate where you live. What are your indoor Temps? Do you have A/C in your house (indoor plumbing? )The average daytime temperature in July here is 95.4*F. So managing heat is a major concern. As you can see from this heat is a always an issue year round:

MonthLowHighJan34.0°F54.1°FFeb38.7°F60.1°FMar46.4°F68.3°FApr54.0°F75.9°FMay63.0°F83.2°FJun70.7°F91.1°FJul74.6°F95.4°FAug74.0°F94.8°FSept67.2°F87.7°FOct56.4°F77.9°FNov45.1°F65.1°FDec36.8°F56.5°F

I think your 2 fans might be adequate if you use one of them to exclusively cool the light. Remember bring air from outside your room across the light and then exhaust to outside your room. Keep in mind where you exhaust your heat to because you don't want it warming the air you are intaking.

2 fans should do the trick but one should be placed right above the lights to suck heat from it right outside.
BUT if you use PC fans would have a real hard time if you'll add a carbon filter later on. If smell is an issue just get a proper inline vent. If not, you would probably be fine.

McFonz said:

I cool the lights with air from my grow room - one less vent. I just use a powerfull one to do so.
If you want to heat up the room you could use the air from the hood to circulate back to the bottom of the plants to heat them up.

Click to expand...

I could be wrong but if he is going to use the 250w HPS, then a aircooled hood is a must. IMO

@ McFonz are you trying to raise your temps in your room or lower them?

Here are the fans I was planing on using http://www.quietpc.com/gb-en-gbp/products/120mmfans/ac-arctic-f12-pro

Will these be hard to wire, or the same as any other pc fan?

I'm starting to think this space is just too small for a hps, even a 250w, although it has almost the same dimensions as the smallest grow tent i can find. Still, it is an upgrade from the closet i was using and im curious to see the difference in results to cfl.

Would i be better off just packing it with as many cfl's as i can?

An air cooled tube isnt really an option because of the width of the box, the cooltube is too long.

tariel said:

I'm starting to think this space is just too small for a hps
Would i be better off just packing it with as many cfl's as i can?

Click to expand...

check out this chart:

cfl 13 actual watts/60 equivalent: 850 lumens
cfl 26 actual watts/100 equivalent: 1,750 lumens
cfl 42 actual watts/150 equivalent: 2,750 lumens
cfl 68 actual watts/250 equivalent: 4,200 lumens
hps 150 watts: 16,000 lumens
hps 250 watts: 28,000 lumens

it takes seven 250 watt equivalent bulbs to equal the light output of one 250 watt hps and uses 476 actual watts to get there. it ALWAYS pays to use an hps if you can find a way to cool it.

An air cooled tube isnt really an option because of the width of the box, the cooltube is too long.

Click to expand...

how about creating a small chamber at the top of the box just big enough for your light and install glass as the bottom of the chamber? then have a passive intake for the top chamber with its own fan and exhaust.

desertrat said:

check out this chart:




how about creating a small chamber at the top of the box just big enough for your light and install glass as the bottom of the chamber? then have a passive intake for the top chamber with its own fan and exhaust.

Click to expand...

I may just do that, althoguh right now im thinking it may just be easier to increase the dimensions of the box to fit a cool tube. That way i can raise/lower it as desired within the box, rather then having it stuck at the top, making it sucky till the plants are a certain height.

tariel said:

I may just do that, althoguh right now im thinking it may just be easier to increase the dimensions of the box to fit a cool tube. That way i can raise/lower it as desired within the box, rather then having it stuck at the top, making it sucky till the plants are a certain height.

Click to expand...

bigger is definitely better for many reasons, so if you can do that, go ahead. if you get stuck and need to consider my idea, you can always place your plants on increasing smaller boxes (or anything convenient) as they grow.

Bonzi Lighthouse said:

I could be wrong but if he is going to use the 250w HPS, then a aircooled hood is a must. IMO

@ McFonz are you trying to raise your temps in your room or lower them?

Click to expand...

I try to lower them most of the time. But I've seen a lot of people in need of heating rather than cooling.

desertrat said:

check out this chart:

cfl 13 actual watts/60 equivalent: 850 lumens
cfl 26 actual watts/100 equivalent: 1,750 lumens
cfl 42 actual watts/150 equivalent: 2,750 lumens
cfl 68 actual watts/250 equivalent: 4,200 lumens
hps 150 watts: 16,000 lumens
hps 250 watts: 28,000 lumens

it takes seven 250 watt equivalent bulbs to equal the light output of one 250 watt hps and uses 476 actual watts to get there. it ALWAYS pays to use an hps if you can find a way to cool it.




how about creating a small chamber at the top of the box just big enough for your light and install glass as the bottom of the chamber? then have a passive intake for the top chamber with its own fan and exhaust.

Click to expand...

A thing to consider is light decayance compared to the distance from the lights.
Using a HPS means you use it with a greater distance, meaning you use far less lumens than what is stated on the light.
With CFL you place the lights very close maximizing the light - using a lot of the lumens.
I like my HPS better than any CFL I've used, but there is more math than simply that.

McFonz said:

A thing to consider is light decayance compared to the distance from the lights.
Using a HPS means you use it with a greater distance, meaning you use far less lumens than what is stated on the light.
With CFL you place the lights very close maximizing the light - using a lot of the lumens.
I like my HPS better than any CFL I've used, but there is more math than simply that.

Click to expand...

actually there's not. light does not decay with distance, it spreads. the lumens don't go down, the lumens delivered per square foot go down by (1/distance squared) as you move away from any light source, hps or cfl. a cfl starts with so few lumens that to get to a decent lumens per square foot ratio the lights have to be very close to the plants to do good. not so with hps. to give an example, two 68 actual watt cfl's and one 13 watt cfl (149 actual watt total) with 9250 lumens total cover about 1 1/2 square feet at 6,000 lumens per square foot (while placed within a couple of inches of the plant). a hps 150, the least efficient hps, has 16,000 lumens that would cover 2 2/3 square feet at the same light intensity while placed about 9 inches away.

as long as budget, ability to cool and space are adequate, hps is always better than cfl. always.