CMH Distance Experience

[Vadim]

For the CMH growers I thought I would share my experience from a distance from light perspective. I have a 4x4' tent and run 2 x 315CMH with Phillips globes. The reason for 2 CMH in the 4x4' tent, is I don't believe you get the strength of light with one and is better suited to a 3x3' grow. I've completed 5 grows now, 4 period and 1 auto. Each time I do an initial from seed and then clone the period plants. I tend to leave the lights at the previous grow height and let the clones go which are started under a 300W CFL, then into CMH tent for a few weeks of 18/6.

What's interesting is I find the clone grows are better with the lights at least 3' from the top of the plants. I get better bud size and density with the clone grows and lights further away.

Attached is a WCH clone. Behind it are some serious SSH clones that also produced awesome bud and quantity. Well over a GPW. I do multi harvest to maximise quality and weight.


What's other peoples experience?

 

[Weaselcracker]

 

[bluter]

think you are spot on total watts per the tent size.

 

[nivek]

heya friend,,

my experience? two days owning a 630w cmh fixture.

i would appreciate picking your brain about distances of light to plant.

i have this light,, not a phillips bulb but a bulb indeed,, 630w double ended i guess

brand new,, and two days i am concerned about fixture distance already. plants exhibiting stress

this fixture in a 48" x 36" space,, right now pushing 20 - 22 inches from canopy and plants are showing leaf curl top leaves

could you provide a bit more detailed info on fixture height that you use,,

appreciated friend

 

[Vadim]

heya friend,,

my experience? two days owning a 630w cmh fixture.

i would appreciate picking your brain about distances of light to plant.

i have this light,, not a phillips bulb but a bulb indeed,, 630w double ended i guess

brand new,, and two days i am concerned about fixture distance already. plants exhibiting stress

this fixture in a 48" x 36" space,, right now pushing 20 - 22 inches from canopy and plants are showing leaf curl top leaves

could you provide a bit more detailed info on fixture height that you use,,

appreciated friend

Hi Nivek, When doing the first grow actual bulb was a good 60cms from top of plant. However, because I was lazy, ok, lets say experimenting :>), I left the lights at their last position. This was as high as they could go using cable ties as the ratchet hangers waste about 4" of grow height. This meant my 2xHi-Par 315W Sunstorm Horizontal Kit - (315W Control Ballast + Philips 315W 930 Lamp + Reflector) in my 4'x4' tent were now more like 100cm from top of plants. The difference between the first and then the clone grow was certainly enough to make the conclusion that having the lights further away helped produce bigger colas. I should also say that my clone grows are never as crowded as the first grow. I typically grow 2 similar strains, so 2 sativa dominant for example and I leave them in veg for a long time. This grow was like 3mths before switch to 12/12, so theres not a lot of room in tent and trying to get in there and defoliate is very difficult. The clone grows however are always not as large so more room but the weight for size is excellent. Example is that I am just finishing a clone grow now and there are 4 plants in very small 1 gallon pots (I wanted to see how these went). I have lots of room and to be honest could've comfortably had another 2 in there. Off these I will pull about 8oz of what looks to be the best bud I've grown.

What is interesting is with one of the strains the first seed grow I found it was leafier than I would like and the although lots of trichomes the leaf when stripped was very thin. I think this was a lack of nutes as I've found you can over do it with Sativa dominant strains. So I increased the feed regime on 2nd grow and the difference in head density, reduced leaf etc is substantial.

Hope this helps

 

[Vadim]

think you are spot on total watts per the tent size.

Thanks Bluter. Yes, certainly the one CMH wasn't sufficient!

 

[bluter]

heya friend,,

my experience? two days owning a 630w cmh fixture.

i would appreciate picking your brain about distances of light to plant.

i have this light,, not a phillips bulb but a bulb indeed,, 630w double ended i guess

brand new,, and two days i am concerned about fixture distance already. plants exhibiting stress

this fixture in a 48" x 36" space,, right now pushing 20 - 22 inches from canopy and plants are showing leaf curl top leaves

could you provide a bit more detailed info on fixture height that you use,,

appreciated friend

how much air are you moving nivek ? it probably is not the light but the heat causing you trouble. you need to move a fair amount more air with an hid fixture.

 

[Vadim]

how much air are you moving nivek ? it probably is not the light but the heat causing you trouble. you need to move a fair amount more air with an hid fixture.

I move about 160CFM via 4" inlet and outlet fans. Seems to work great. I bit noisey but not an issue for me.

 

[nivek]

Well,, i think you

how much air are you moving nivek ? it probably is not the light but the heat causing you trouble. you need to move a fair amount more air with an hid fixture.

are correct about that friend,, cheers

 

[Cornercat]

You are right about a single 315w CMH not being enough for a 4x4' and probably best suited in a 3x3'. Here's a graph I made when I measured the PPFD of a CMH in a 4x4 tent. I took PAR readings every 6" and color coded them by hanging height.

The intensity of PPFD drops off significantly and immediately outside of the dimensions of the reflector. YMMV with the type of reflector of course. Looking back at this graph, it's really not even enough for a 3x3. 12" above the canopy gives ~900 average ppfd in the 2x2' spotlight below it, which is really good. But anything outside of that spotlight would be photosynthesizing at ~25% capacity.

Clones only need ~100 PPFD while rooting, scaling up to 500-600 by late veg. You want 600+ PPFD during flowering to maximize photosynthesis without co2.

 

[Vadim]

You are right about a single 315w CMH not being enough for a 4x4' and probably best suited in a 3x3'. Here's a graph I made when I measured the PPFD of a CMH in a 4x4 tent. I took PAR readings every 6" and color coded them by hanging height.

The intensity of PPFD drops off significantly and immediately outside of the dimensions of the reflector. YMMV with the type of reflector of course. Looking back at this graph, it's really not even enough for a 3x3. 12" above the canopy gives ~900 average ppfd in the 2x2' spotlight below it, which is really good.

Clones only need ~100 PPFD while rooting, scaling up to 500-600 by late veg. You want 600+ PPFD during flowering to maximize photosynthesis without co2.

Thanks CC, Excellent and very interesting. Do you know why on the edges the PPFD rises the further the light is away? Is it a case of the hood restricting light going at that far and is more a refracted light and or reflection from the tent walls?

Thanks
Vadim

 

[Cornercat]

Thanks CC, Excellent and very interesting. Do you know why on the edges the PPFD rises the further the light is away? Is it a case of the hood restricting light going at that far and is more a refracted light and or reflection from the tent walls?

Thanks
Vadim

You got it. The higher you hang them, the more the light bounces around and reaches the edges. Here's a graph of a 120 degree LED chip. 120 degrees is a common angle for reflectors too.

Companies determine the beam angle by measuring where the light drops to 50% intensity from the peak. So a 100w light at 120 degrees is always going to be halving its intensity on the edges, that's part of the inverse square law. Companies tell you to hang the lights higher to compensate for this, so more of the tent falls within the center half of the angle. The problem is the inverse square law also halves intensity by distance too. Any gains on the edges by hanging a light higher means losses in the center. PPFD graphs help find that compromising height where you still have intensity in the center but are spreading it as wide as you can.

This is good to know because the higher you hang your lights, the more that light energy depreciates before it reaches the canopy; meaning wasted electricity. If efficiency is a concern, the best way to overcome the limitations of beam angle and the inverse square law is to hang many lights spread out evenly over the entire footprint, as close as possible without burning your plants. 6" away is ideal if you want the most radiation reaching your plants per watt. 6" with any HPS, CMH, and most LED fixtures would burn the plants though so you have to get creative. LED is the only real efficient option since you can spread out hundreds of chips across a 4x4. Here's the PPFD graph for the SpydrX Plus LED, which does just that.

Here's a table that compares the Spydr to the 315w CMH. Notice how the Spydr maintains even coverage across a 4x4, allowing it to be hung as close as 6", while all the other lights severely drop off as they try to cover the 3x3 and 4x4 zones from their center spotlight with 120 degree angles.

 

[Vadim]

You got it. The higher you hang them, the more the light bounces around and reaches the edges. Here's a graph of a 120 degree LED chip. 120 degrees is a common angle for reflectors too.

Companies determine the beam angle by measuring where the light drops to 50% intensity from the peak. So a 100w light at 120 degrees is always going to be halving its intensity on the edges, that's part of the inverse square law. Companies tell you to hang the lights higher to compensate for this, so more of the tent falls within the center half of the angle. The problem is the inverse square law also halves intensity by distance too. Any gains on the edges by hanging a light higher means losses in the center. PPFD graphs help find that compromising height where you still have intensity in the center but are spreading it as wide as you can.

This is good to know because the higher you hang your lights, the more that light energy depreciates before it reaches the canopy; meaning wasted electricity. If efficiency is a concern, the best way to overcome the limitations of beam angle and the inverse square law is to hang many lights spread out evenly over the entire footprint, as close as possible without burning your plants. 6" away is ideal if you want the most radiation reaching your plants per watt. 6" with any HPS, CMH, and most LED fixtures would burn the plants though so you have to get creative. LED is the only real efficient option since you can spread out hundreds of chips across a 4x4. Here's the PPFD graph for the SpydrX Plus LED, which does just that.

Here's a table that compares the Spydr to the 315w CMH. Notice how the Spydr maintains even coverage across a 4x4, allowing it to be hung as close as 6", while all the other lights severely drop off as they try to cover the 3x3 and 4x4 zones from their center spotlight with 120 degree angles.

Thanks CC for the detailed response. What I find really interesting is that by having my 2x315w CMH hoods further away, I get better end product as it's fatter, denser and most importantly stronger!
So as stated whenever I do clone grows, I leave the lights as high as they can. So the lights can be some 36" at least from the top of the plants. LED interests me but I have already invested in CMH and the globes have a ways to run yet. The reason I went down the CMH route was at the time I read a report where they claim more trichomes under CMH. Well I can't confirm or deny that but I can confirm what I grow works very well!

 

[cr8grow]

I have 3.5 grows now with one CMH 315w in a custom 3’x3’ grow cabinet. Ive maintained 24” height from the top of the canopy. I use Philips bulbs, 4k for veg and 3k for flower. Bud quality has been excellent and Im very happy with the light, perfect for my cabinet. My latest grow Im letting them all go natural with no training and these are taller Green Crack autos. Im now 22” from the main bud and will probably be testing 18” if they keep stretching at 5 weeks in from sprout. A couple pics from my grows and the latest just starting to flower out.

 

[Weaselcracker]

This 36” concept is basically very bad news for my plans of buying a CMH. I think the fixture is quite big -taking up at least 12 inches of space- correct me if I’m wrong. Plus presumably you don’t want to jam it against the ceiling so there’s a couple more inches. Then another 12 inches or so for the pot, and I’m only left with room for tiny midget plants. Currently most of my plants are around. 4’ or more.

@nivek how are things going for you with the new CMH?

 

[Enjoil]

I got a 315 and my plants LOVE it. I’ve had it about 3 months now so I got one run vegged and flowered with it and halfway through current run... it seems they can get to within about a foot til they start to freak out. I try to keep mine about 16-24inches 30 inches for transition period. Two/3 weeks ..then lower it a bit.

 

[SmokeLake]

I am running 2x315 cmh in my 4x4 tent its a great amount of light 1 was not enough but the heat is the biggest issue. I have direct vent outside to remove humidity from my home and had to add an inlet fan to get enough air flow to prevent the tent from being constantly sucked in along with atleast 3 corner fans. I find I will get PM if I reduce airflow not sure if its the humidity or a byproduct of my tent being in my 70 year old homes basement. I find regularly spraying down with neem seems to help but i dont want to soak buds with neem. Ive often wondered about using outside air but filtering and warming during winter months may pose the biggest hurdles.

 

[Slowpuffer]

For the CMH growers I thought I would share my experience from a distance from light perspective. I have a 4x4' tent and run 2 x 315CMH with Phillips globes. The reason for 2 CMH in the 4x4' tent, is I don't believe you get the strength of light with one and is better suited to a 3x3' grow. I've completed 5 grows now, 4 period and 1 auto. Each time I do an initial from seed and then clone the period plants. I tend to leave the lights at the previous grow height and let the clones go which are started under a 300W CFL, then into CMH tent for a few weeks of 18/6.

What's interesting is I find the clone grows are better with the lights at least 3' from the top of the plants. I get better bud size and density with the clone grows and lights further away.

Attached is a WCH clone. Behind it are some serious SSH clones that also produced awesome bud and quantity. Well over a GPW. I do multi harvest to maximise quality and weight.


What's other peoples experience?

heya friend,,

my experience? two days owning a 630w cmh fixture.

i would appreciate picking your brain about distances of light to plant.

i have this light,, not a phillips bulb but a bulb indeed,, 630w double ended i guess

brand new,, and two days i am concerned about fixture distance already. plants exhibiting stress

this fixture in a 48" x 36" space,, right now pushing 20 - 22 inches from canopy and plants are showing leaf curl top leaves

could you provide a bit more detailed info on fixture height that you use,,

appreciated friend

I've been running a Nanalux 630w fixture for about 3 years now, and one thing I've found for sure, I can never let the light get inside the 2 foot zone. Also heat was a problem and I've added extra circulation fans. i start my seeds under cfls, and move to a tent with one 315w cmh 4200, and then too the 630 tent when they're ready to bloom ! And I do believe a phillips 630 will perform better or equal to a 1000w hps. Even a single 315w will burn your plants, if it gets inside 18 inches. i believe they are the cheapest bulbs, when ya take into account they last twice as long as hps and are cheaper to run. When led prices make it down to earth, maybe I'll build one ?? Good luck with new fixture nivek !!
I'm hating it here in Caronaville !!

 

[nivek]

ok,, what a messa fantastic information and opinions from y'all,, thanks for it all.

i will be back to edit this as at the moment i am raising my 630w cmh as high as i can,, which will give me a healthy 24" to canopy, which i have gleaned as the "possibly recommended height whilst being open to adjustment.

to go more than 24" i would need to lower the shelf the plants sit on,, which is not a problem at all, to a degree.

ok, back in a bit,, light is cooled now

 

[nivek]

ok,, i have only had said liight for a couple of weeks now so i won't comment on things i don't know,,

but,, there are some things i do know now,, as in

the light was larger than i thot, quite a bit actually, but i just thot too small,,

the light was easy to put together and install,, i have it in a 48 x 36" space

my ventilation and air movement have meant the light has not been too hot,, and has even had the temps just right,, 26, 27c

i had the light on the underside of 20" from the canopy and i think i noitice the more toppish leafs curling a bit too much to indicate pleasure,,

as in this pic perhaps,, it appears noticeable,,

tho maybe that issue is all over

anyway,, light is now the upside of 24" now so i will be watching,, indeed

thanks friends,, i bot this light just to spice things up a bit, and other reasons,, i have led's as well,, plenty of em actually,, ha

variety is indeed 'a' spice of life

cheers