Effect of Light Intensity Reduction

[ak-51]

So I'll frame my question with my situation to make it clearer, although this issue could be applied to any number of scenarios.

I'll be going away for about 5 days next month. Most of my stuff is pretty automated. Feeding and watering is pretty much on autopilot, and I feel confident that those won't be a problem within that time frame. What I'm concerned with is the lights. Up until now I have been home to open and close my tent and veg closet doors during the correct times to make sure there's no light leaks or anything. Being gone will mean that if the setup is left as it is, the tent will have to remain closed and the closet too. I don't like the idea of them being closed for that long, mainly because I am paranoid about heat build up. A 318w LED is running in the closet, and there's no ventilation in there unless the door is open. The only ventilation for the tent is a 6" fan and scrubber that exhausts air outside of the tent, intake is passive. The tent has a 1000w HPS that is cooled on a closed loop; air from outside the room runs through the hood then exhausts right back outside the room.

I was looking into getting a high-heat shut off, but the one's I saw at the hydro-shop were only for 120v. I run 240 and the only way I could hook up that high-heat shut off would be to put it on the trip-cord for a light controller. Kind of overkill for just a single 1000w.

I am looking at lowering the light levels a bit to mitigate any possible heat issues. I would like to turn my HPS down to either 750 or 600 while I'm out and possibly replace the light in the veg room with a few CFLs.

The girls in the tent will then be about 36 days into flower. The veg tent has various size plants, the largest being only about 14-16 inches tall.

Now I'll just flat out state that the better option for me is to move the vegging plants into my bedroom while I'm gone. That way they'll be out in the open and the tent will be able to remain open since there will be no other source of light in that room. I'd still like to hear from anybody on the effects of reduced light though. Keeping the same light schedule should not disrupt the flowering of the girls right? Cloudy days happen, so they shouldn't freak out and herm on me or anything. Right?

Side Question: A C.A.P. Cycle Timer is critical to my feeding system. Failure would mean some plants not getting fed and possibly a flood. Anybody have anything to say about their reliability? The function of the photocell or precise intervals to the second are not important to me. The only thing that matters to me is whether or not it reliably turns on and off; not "sticking".

 

[messn'n'gommin']

They tend to stretch with reduced light and the shortened light schedule will start them into flowering. Granted, going back to a regular veg cycle would reverse that, but it will take a few days for them to get back on track.

What are temps inside the tent and closet like with the doors closed? With the light on a closed loop and a fan and filter ventilating the tent, you shouldn't have all that much heat to deal with. A window A/C unit would take care of any excess heat, though.

 

[wahtever]

There's lots of hydro stores in your area, did you try all of them? Fire is bad.

I was in the shop when you were talking to them (him).

 

[smokefrogg]

I was in the shop when you were talking to them (him).

damn that'd freak me out to read if i was the op

 

[ak-51]

They tend to stretch with reduced light and the shortened light schedule will start them into flowering. Granted, going back to a regular veg cycle would reverse that, but it will take a few days for them to get back on track.

What are temps inside the tent and closet like with the doors closed? With the light on a closed loop and a fan and filter ventilating the tent, you shouldn't have all that much heat to deal with. A window A/C unit would take care of any excess heat, though.

I won't be changing the amount of time they're lit, I was just looking into dimming the 1000w and swapping out the LED for a few CFLs.

The tent currently runs in the high 80s with the doors all closed up. I do have a window A/C running in the room that both the closet and the tent is in. I think if I get a fan in the room circulating air better it will help the A/C cool the tent and closet more efficiently, rather than just having the heat all build up. I think having some sort of active intake for the tent would really be a big plus.

Good to know about the stretching though, because for the stuff in the tent that is a huge issue for me right now. My last run I had issues with light bleaching. That was with LEDs. I'm guessing now that I'm running HPS in there if they get too close to the light it'll be bleaching and heat stress as well. That's really something I'm trying to avoid.

There's lots of hydro stores in your area, did you try all of them? Fire is bad.

I was in the shop when you were talking to them (him).

I doubt you know me.

damn that'd freak me out to read if i was the op

I doubt that dude knows me. It is kind of ominous though right?

 

[messn'n'gommin']

Sorry, I didn't mean that raising the light was necessarily a bad thing. One would ordinarily do that anyway as the plant grows taller. Just raise it enough that when you get back it will have grown to the light rather than into the light.

Still, the high 80's is pretty high for a closed loop system. I would think, even with a filter, a 6" fan should help to keep temps down.

How warm does it get in the room the tent is in?

What kind of fan are you using for the closed loop?

For your tent, how is the ventilating system setup?

 

[ak-51]

The thing is that the light is already raised about as high as it can go and the table is dropped about as low as it can go. I really have to quit letting them veg for so long.

The room swings pretty wide on temps. Part of the problem is that the A/C unit is shit. It's plenty powerful, but it seems to allow very wide deviation from it setpoint before it kicks on. I'm experimenting with having a fan blowing over it all the time to try to get the temperatures more even in there.

I have a 10" fan on the closed loop. From the window to the tent is 10" ducting, inside the tent is 6". All ducting is insulated, but the hood is not. The fan is pulling through the hood rather that pushing.

The only ventilation for the tent is the carbon scrubber and 6" fan inside that pulls air out into the room. Intake is passive, there is one mesh vent (Secret Jardin) open and two 6" ports that have duct in them with a couple bends to mitigate light leaks. I'd like to get some kind of active intake.

 

[Green lung]

You could leave led in the veg with door closed. I have found plants can tolerate high heat no problem in veg.

 

[messn'n'gommin']

What are temps like in the room with the tent and closet?

Pic's would be good!

 

[ak-51]

The door into the room is on the upper right hand side; it swings into the room. The closet, which is being used for veg, is on the bottom right and it has two folding type doors that slide on tracks to open. The window is on the left wall, the A/C unit is directly below the window.

My 5x5 Secret Jardin tent is in the center of the room. There is a 3x3 table inside of it (dark green). It is running a 1000w air-cooled light on a closed loop. Air is drawn from outside through the window in a 10" duct (blue), this duct is reduced to 6" as it enters the tent. It runs through the hood then is expanded back to 10" as it exits the tent again. There is a 10" in-line fan (red circle) that is pulling through the system, it then exhausts the air back out the window (red).

There is a small 6" carbon scrubber inside the tent. The 6" in-line fan that pulls through it is also inside the tent. 6" duct comes off of that and exhausts the scrubbed air outside of the tent. That duct comes out of the top port and is positioned so that when the door is open it blows the clean air out the door, into the hallway (top orange arrow). When the door is closed it just deflects off the door and recirculates in the room (bottom orange arrow).

The negative pressure that the scrubber generates pulls air in. There are two duct ports which have short runs of duct in them, but are open on either end, and one of the mesh vents is open on the opposite side (all passive intakes highlighted in light blue).

There are two circulation fans in the room. One is inside the tent. It is on the rear-right corner and blows air in between the canopy and the hood (blue). The other is a larger oscillating fan in the lower right corner (blue), this one covers 90 degrees, and blows from that corner over both the A/C unit, the surface of the tent, and the doors of the closet.

 

[ak-51]

There are a few problems with this setup:

1. Both the exhaust from the tent's scrubber and 2 of the passive intakes are on the same side, and in a somewhat small area. A lot of the hot air run out the scrubber exhaust probably just gets sucked back into the passive intake. When the door is open the exhaust just blows out the door and this isn't a problem.

2. 2 10" insulated ducts are right in front of the A/C unit, harming circulation.

3. Since the exhaust and intake both have to be on the same side it requires more turns of the duct-work and increases resistance.

 

[messn'n'gommin']

Thank you for the diagram! I'm much more visual than imaginative and I appreciate your patience with me!

That's one of the first things I noticed, is poor cross flow of air inside the tent itself. Although, an oscillating fan will help with that.

If possible, remove the dual window fan and try for a deflector, or some way of separating the intake and exhaust ports for your light. Otherwise, do your best to draw from upwind and exhaust downwind.

Short of heavy LST/supercropping you may well have to dim your light, since you'll have at least a couple weeks more of stretch and height is turning out to be a bit problematic. Scrog/LST/supercropping will go a long way to keeping height problems at bay and will fill up your tent with a nice even canopy!

hth...and please...keep us posted!

 

[inquest]

Ak, I've had an idea for limiting the heat released from a HID hood. Althought I've not tried it yet, it might be worth looking into.

Basically, just wrap the outside of the thing with waterheater insulation and where the glass is, just silicone/glue one or more pieces of glass to it. Make sue to leave a sealed airspace between the panes of glass. Voila! Triple pane glass! Silicone is good to 700-800F, btw.

Also, insulated ducting might be worth looking into. Or wrap in yourself with the left over waterheater wrap.

On the light intesity point, I've had to reduce intesity on my mother plant before (24/0 schedule) and it caused her to push out a small amount of flowers and to stretch a bit. She looked like a clone under 12/12 right when you start to see flowers. Took about a week or so to do that, though, and it didnt continue very long.

 

[wahtever]

A ten inch fan is a LOT for cooling a 1000W (assuming regular vortex, max fan, etc.). I bet the top of your hood is cold to the touch, meaning the only heat your getting from your light is from the lights radiation. Unavoidable, but it will decrease if you turn down your ballast.

Just a thought, but if it were me I would change the closed loop 10" from pull to push, only because I'd be worried about a small air leak dumping dirty air outside. There's also the possibility of ducting coming loose and then you'd be dumping tent air outside. Also 10 inch reduced to 8 inch will cut the air flow roughly in half. I can only guess that decreasing to 6 would decrease it to about 25%. The only reason I bring this up is that if noise is a possible issue than you could probably get away with running a much smaller fan and not see a noticeable rise in temp.

The adjustable ballasts are great for mitigating temperatures, but you will need to adjust your hoods height to avoid stretch. It's a trade off if you're leaving because in one scenario your girls will have more space to grow without topping out, but if they grow enough they will face higher temps and high light levels, and the other you'll have lower temps but not as much room to grow. A larger hood will spread the radiation heat over a larger area. I've seen plants pressed right up against the glass of a 1000W XXXL without a problem (other than bleaching). Although when left there fore 2+ days I have seen charring on some (~25%). Since you've probably have such a cool hood you most likely don't have to worry about plants burning, and there's worse things than bleached tips. A good trim job should be able to take care of that. Also note that 1000W provides roughly 1.5 feet of penetration. If your plants have tall plants with a dense canopy than stick with 1000. If they're short and sparse there should be no adverse effects of switching to 600. Also keep in mind that if you change your light wattage your nutrient needs will change. Higher light wattages require higher TDS.

A good product to mitigate stretch is Bushmaster. But be VERY careful with this product. I wouldn't recommend it just to combat a 5 day trip, but if your strain is stretchy you may want to investigate.

For a five day period I wouldn't sweat it. It seems that your setup is pretty solid. Just pop your hoods up a little more than normal. It sound to me you like you probably run your plants too close to the hoods (as evident by the bleaching). 18 inches is pretty standard for a 1000W light.

I don't know you, I just happened to overhear someone discussing the exact same scenario with a grow shop the day before you posted. Could definitely be a coincidence, as many people prefer to run 240V. I also would like to reiterate that I still believe you should run a high heat shutoff, not only to protect your plants, but more importantly to protect your home.

 

[ak-51]

Just a thought, but if it were me I would change the closed loop 10" from pull to push, only because I'd be worried about a small air leak dumping dirty air outside.

While that is a concern that I considered, my reasoning for setting it up to pull was that it wouldn't be possibly pushing hot air out of leaks. Hot air moving over my fan and the possibility of leaking stinky air are important. In my next setup I would much rather push. I'll probably be keeping this one for the remainder of this run, only about another month at this point. Then I'll switch a few things up. I like trying new setups, I learn what works and what doesn't and try to improve the next run.

Also 10 inch reduced to 8 inch will cut the air flow roughly in half. I can only guess that decreasing to 6 would decrease it to about 25%. The only reason I bring this up is that if noise is a possible issue than you could probably get away with running a much smaller fan and not see a noticeable rise in temp.

Yeah. While I think my initial reasoning for running a larger fan at a lower speed for noise reduction was grounded in logic, at this point I don't think it was the best idea either. Reducing from 10" to 6" is too much IMO. If I were still running the thing at half speed with my variac it would be one thing. Having it setup pulling I don't feel comfortable running temps over 100F through my fan, so I have it up all the way now and it runs anywhere from 80F to 90F (between the hood and the fan).

It sound to me you like you probably run your plants too close to the hoods (as evident by the bleaching).

Yes. I have run my plants too close to the hood this run. This and my last run I have had some light bleaching effects. The last run was with LED so I still have remnants of that idea that I can run 6" from the lights and be ok, which is not at all kosher with HPS. The other mistake I have made for this run and the last has been underestimating how much they'll stretch in flower and flipping them to 12/12 too late.

I don't know you, I just happened to overhear someone discussing the exact same scenario with a grow shop the day before you posted. Could definitely be a coincidence, as many people prefer to run 240V.

Seems like it's probably a coincidence, but I guess it could have actually been me. Oh well.

I also would like to reiterate that I still believe you should run a high heat shutoff, not only to protect your plants, but more importantly to protect your home.

I agree 100%, safety first. I have to run 240v right now because of the lack of balls that all of my other breakers have. The 240v line runs the light fine and takes 75% of the stress off the rest of the breakers which run everything else. I would really feel a lot better having a high-heat shutoff. It's either buy the whole light controller rig for $$ or figure out a way to run 120v for my ballast so I can use just the high-heat shutoff module.

 

[ak-51]

I decided to take the prudent course and move the vegging plants out of the closet that was next to the tent and into my bedroom temporarily. I'll be gone anyway so it won't matter. This way all plants can get sufficient circulation and I'll worry less while I'm away.

The room has been a little better recently though. After adding a couple of fans and turning down the A/C more ambient temperatures have not exceeded 86 degrees. It would probably have been ok to leave everything the way it was while I was gone, but this way is just better for now. I might move them back when I get back.

Thanks for the help everybody!

UPDATE: I got back from vacation and everything was ok. My whole place smells like reefer, but nobody was here so that's ok I guess.