SF G4500. How much light in flower?

This is my second grow with the SF GS4500, and so far it's been great. However, I have been trying to figure out how much intensity would be appropriate for each stage. I have pretty much ran it at 100% since flipping to flower, but now I wonder if that intensity is even needed until they start actually budding? Does the 2-3 week stretch benefit from the higher light intensity? At what point in flower would you do 80%, 90%, 100%? I find around 60% or so seems to work fine for veg, but I know pushing it in flower actually increases yield, but would I need to worry about anything like C02 issues at max? I run an ACI S6 currently at around 5/8 speed so I can definitely move the air if needed. Also the manufacturer hanging distance for flower seems pretty close; I've had some curly margins in leaves that are that close to the light. These GG4 IHG stretched more than expected and it stays hot in the room, so any justification to lower the lights a bit would be welcome as long as it doesn't come at the expense of yield. Otherwise I'd say the light has been great thus far. Removing the driver from the tent certainly helps, but the lights themselves at max can definitely push the tent to 85 degrees if I don't have the house HVAC set to 71.

100% will give you max performance plant wise and intensity wise, dimming is good if you can't afford to move your light higher or your space becomes too hot.
You don't need to worry about co2 at those levels no, just make sure fresh air gets in.
No justification to dimm your high value more light producing system, otherwise you could have just bought a hps or 1/2 output led system
You wanna use as much light as you can within a good range of temp and rh.
Sure in seedling stage you don't need to be on 100%, but that's common knowledge.
Veg in 60% ? Why ? No good reason if you can handle the conditions 100% makes.
Same in flower, you are in a 65+- days race to the finish with each day is a big factor on what your final results will be, you don't wanna miss a day in terms of over saturation (light) proper waterings, leaf management etc, everything you do with added benefits will show in your harvest.
So no, no logical reason to dimm your lights at any stage really if you can handle the electricity, heat, rh, etc.

DanKiller said:

100% will give you max performance plant wise and intensity wise, dimming is good if you can't afford to move your light higher or your space becomes too hot.
You don't need to worry about co2 at those levels no, just make sure fresh air gets in.
No justification to dimm your high value more light producing system, otherwise you could have just bought a hps or 1/2 output led system
You wanna use as much light as you can within a good range of temp and rh.
Sure in seedling stage you don't need to be on 100%, but that's common knowledge.
Veg in 60% ? Why ? No good reason if you can handle the conditions 100% makes.
Same in flower, you are in a 65+- days race to the finish with each day is a big factor on what your final results will be, you don't wanna miss a day in terms of over saturation (light) proper waterings, leaf management etc, everything you do with added benefits will show in your harvest.
So no, no logical reason to dimm your lights at any stage really if you can handle the electricity, heat, rh, etc.

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I thought maximizing light didn't matter as much in veg. I'll have to find the research, but I thought increased light intensity didn't lead to increased growth in veg as compared to flower.

Naive to assume I guess...
More light or what you call light intensity, always leads to more growth when you have your environment dialed, no matter veg or flower.
you just need to make sure your plant can absorb that high intensity light, if he has enough leaves to catch all that light, if the rh and temp is right etc..
Either way, a 1500ppfd is a very good value, your not over stepping here into alien grounds haha, an hps will give probably double ppfd right in the center under it at the right height and people have grown like this for years with excellent results with no added co2,but sure if you add when you get to those values it can always be better.
The added value of your light system is to be able to spread those 1500 +- to every spot in your space, which hps can't.

Attached paper may provide some insights.

Re don't need high light in veg - lots of recommendations for what I call "modest" amounts of light and, to date, none of them offer any rationale. There may be many reasons for those recommendations and I have to expect that one reason is ignorance, the other might be self-interest.

On the latter point - it is in the best interests of all involved that a vendor giving recommendations about how to use a product err on the side of caution. The user will tend to have a positive experience even if that experience is less than "optimal".

There's nothing wrong with running 600 in veg and in flower, for that matter. Cannabis will give a really good crop at that light level. That doesn't mean that growers shouldn't make the conscious decision to use higher light levels. Of course, the rest of the grow has to be able to support the increased level of growth and that's where a lot of growers hit the wall.

A puzzling pair of dichotomies:

Research indicates that crop quality and crop yield increase as light levels increase. If a plant receives extreme levels light, the symptoms arise quickly, the symptoms are obvious to the naked eye, and the problem is easily and quickly resolved by turning the dimmer down.

Research indicates that high nutrient levels lead to toxicity. If a plants receives extreme levels of nutrients, the symptoms may not arise for days or even weeks, the symptoms can be very hard to properly diagnose, and the problem can be very hard to resolve.

So let's keep our light levels low but push lots of nutes.

"lots of leaves" - per the Frontiers paper and other sources - plants grown under high light levels will tend to have more, smaller leaves than plants grown under lower levels of light. Perhaps that allows the plant to control transpiration more effectively?

Re. 1500 - the highest I've run is 1050, above that level I start to see tacoing. In veg, I run DLI's in the 80's but, for photos, 42 or 43 in flower. Autos? In my experience, they're beasts. Huge amounts of light and "back up the truck" yields.

RuggedWombat said:

This is my second grow with the SF GS4500, and so far it's been great. However, I have been trying to figure out how much intensity would be appropriate for each stage. I have pretty much ran it at 100% since flipping to flower, but now I wonder if that intensity is even needed until they start actually budding? Does the 2-3 week stretch benefit from the higher light intensity? At what point in flower would you do 80%, 90%, 100%? I find around 60% or so seems to work fine for veg, but I know pushing it in flower actually increases yield, but would I need to worry about anything like C02 issues at max? I run an ACI S6 currently at around 5/8 speed so I can definitely move the air if needed. Also the manufacturer hanging distance for flower seems pretty close; I've had some curly margins in leaves that are that close to the light. These GG4 IHG stretched more than expected and it stays hot in the room, so any justification to lower the lights a bit would be welcome as long as it doesn't come at the expense of yield. Otherwise I'd say the light has been great thus far. Removing the driver from the tent certainly helps, but the lights themselves at max can definitely push the tent to 85 degrees if I don't have the house HVAC set to 71.

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Heh, just wanted to say that's a Great f'ing light!

I've been using Growcraft for three years, veg and flower. They were great in their day but they just don't have the uniformity like the G4500. The SE7000 had great output and uniformity and Spider did it even better with the G4500.

Re. light levels - get a light meter. The Uni-T is only $32 and it will get you right in the zone very quickly.

How much light? As much as the plant can consume. If you're getting tacoing, that's the light saturation point for that plant at that time. Well done! Drop it back a bit and you're golden.

Re. CO2 - if you can add CO2, do it. It improves photosynthesis rates at "all" light levels.

Light levels drop off very quickly. In my current grow, I can drop PPFD by 50µmol by raising the light 1". That's why having a flat canopy is so important.

Just found this the other day.


Your canopy looks great. It looks flat but not level. If that's the case, tilt the light. Sounds strange but it will help get an even cast of light across the canopy.

Delps8 said:

Heh, just wanted to say that's a Great f'ing light!

I've been using Growcraft for three years, veg and flower. They were great in their day but they just don't have the uniformity like the G4500. The SE7000 had great output and uniformity and Spider did it even better with the G4500.

Re. light levels - get a light meter. The Uni-T is only $32 and it will get you right in the zone very quickly.

How much light? As much as the plant can consume. If you're getting tacoing, that's the light saturation point for that plant at that time. Well done! Drop it back a bit and you're golden.

Re. CO2 - if you can add CO2, do it. It improves photosynthesis rates at "all" light levels.

Light levels drop off very quickly. In my current grow, I can drop PPFD by 50µmol by raising the light 1". That's why having a flat canopy is so important.

Just found this the other day.
View attachment 5378837

Your canopy looks great. It looks flat but not level. If that's the case, tilt the light. Sounds strange but it will help get an even cast of light across the canopy.

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Yeah the left 2 plants aren't having any issues, but the right one is definitely getting some crispy margins and tips. I'll have to measure them, but they are probably within 6 inches from the light which is pretty toasty. I may try to LST them down further, but I'm guessing the alternative is trim the burned parts or lower the lights, but I'd hate for one plant to ruin it for the whole class. They are GG4 so honestly the stretch you see is after I tied them down as they wanted to high five the light. I'm also going to cool off the EC a bit as I've been doing around 1.6-1.8 with some tip yellowing. I'm feeling pretty confident with the sheer amount of foliage left at this stage; I just need to determine what I'm willing to compromise on to help the right plant that is being a bit greedy on light.

ruggedwombat if you don't want to lst the tall one,kinda late to anyways since they in flower.just put something under the shorter ones to even the canopy ,then you can raise the light so the tall one is not getting burnt. nice plants good luck

RuggedWombat said:

Yeah the left 2 plants aren't having any issues, but the right one is definitely getting some crispy margins and tips. I'll have to measure them, but they are probably within 6 inches from the light which is pretty toasty. I may try to LST them down further, but I'm guessing the alternative is trim the burned parts or lower the lights, but I'd hate for one plant to ruin it for the whole class. They are GG4 so honestly the stretch you see is after I tied them down as they wanted to high five the light. I'm also going to cool off the EC a bit as I've been doing around 1.6-1.8 with some tip yellowing. I'm feeling pretty confident with the sheer amount of foliage left at this stage; I just need to determine what I'm willing to compromise on to help the right plant that is being a bit greedy on light.

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Or just raise the light a bit though there are limits.

I ended up buying a Vipar XS 1500 for the plant on the left.

pghdave420 said:

ruggedwombat if you don't want to lst the tall one,kinda late to anyways since they in flower.just put something under the shorter ones to even the canopy ,then you can raise the light so the tall one is not getting burnt. nice plants good luck

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Unfortunately the picture probably doesn't show it, but the GS 4500 is at max height and to the point where part of the exhaust fan and filter itself is actually running between the light bars. I should have gone with a lower stretch indica, but the siren call of sweet stank was more than I could bare.

RuggedWombat said:

Unfortunately the picture probably doesn't show it, but the GS 4500 is at max height and to the point where part of the exhaust fan and filter itself is actually running between the light bars. I should have gone with a lower stretch indica, but the siren call of sweet stank was more than I could bare.

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Can't raise the right side - how about dropping the left side?

Plants are doing well. At F47, they are on the home stretch. I lowered PPM to around 600 and adjusted the light to around 80% for 1000 PPF. The plants are showing some signs of small fox tails, so I'm backing off the light from 1262 to 1000 PPF. DLI is now 37 though I can't account for PPF at this close range without a reliable light meter so going off of manu specs. You can see the right side took a beating from being so close to the light combined with the temps in the low to mid 80s for quite some time. I may attempt 100% with next grow and keep them much shorter. They have more than enough foliage to survive the rest of the grow though so overall pretty stoked.

RuggedWombat said:

Plants are doing well. At F47, they are on the home stretch. I lowered PPM to around 600 and adjusted the light to around 80% for 1000 PPF. The plants are showing some signs of small fox tails, so I'm backing off the light from 1262 to 1000 PPF. DLI is now 37 though I can't account for PPF at this close range without a reliable light meter so going off of manu specs. You can see the right side took a beating from being so close to the light combined with the temps in the low to mid 80s for quite some time. I may attempt 100% with next grow and keep them much shorter. They have more than enough foliage to survive the rest of the grow though so overall pretty stoked.

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Beautiful colors in there and the huge win is that you didn't let any photons hit the floor. That's great! I've done a few grows with just one plant (in a 2' x 4') so I'm only getting about ⅔ of the benefit of my light. You're at 100% so it'll be "back up the truck" at harvest!

I've a g5000 I had mines 100 percent the last few weeks It didn't bother them
Yours looking good man they should be solid buds anyway man

joesoap2013 said:

I've a g5000 I had mines 100 percent the last few weeks It didn't bother them
Yours looking good man they should be solid buds anyway man

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Yeah I turned it down to 50% which at the insanely close distance is still around 33 DLI. I think cranking to 100% was foolish in my case as the increased photons didn't matter since I greatly exceeded my DLI and the additional light and heat created margin rolling and especially foxtailing. You can see it in the pics. Luckily, learning more on light helped me dial it in and I'll have a better understanding for next grow. They are still finishing great, but light does have a cap without C02 supplementation. Here they are at F58. You can see the tall heads on the left plant and definite fox tails starting on the right one which is closest to the light. Still super happy with results, but always room to improve. Note the vertical leaves on the right plant due to stress.

RuggedWombat said:

Yeah I turned it down to 50% which at the insanely close distance is still around 33 DLI. I think cranking to 100% was foolish in my case as the increased photons didn't matter since I greatly exceeded my DLI and the additional light and heat created margin rolling and especially foxtailing. You can see it in the pics. Luckily, learning more on light helped me dial it in and I'll have a better understanding for next grow. They are still finishing great, but light does have a cap without C02 supplementation. Here they are at F58. You can see the tall heads on the left plant and definite fox tails starting on the right one which is closest to the light. Still super happy with results, but always room to improve. Note the vertical leaves on the right plant due to stress.

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I rarely if ever go over 800ppfd in flower. Just because you can doesn't mean you should. Haha. Honestly though I get way better grows when not running in the red.