Transition from MH to LED

[BigBudsBunny]

I will be transitioning from Metal Halide 400w to a mars hydro fc 3000 evo with the 301h diodes. This is in my 4x4 veg area where there is seedlings, clones, and vegging plants. I keep the canopy even here for vegging and the established clones by using risers and keep seedlings further away. The MH light is approximately 18" from the top of the canopy at 75% power (300w). I was wondering how high I should start the led for transition and at what power level to start at. My guess is I should start them at a set height say 24" or 18" and adjust the dimming as they get acclimated to it rather than raising and lowering the light. - is this the right thought concept?

 

[Sparkey224]

Those Mars FC 3000 are pretty strong lights. I usually start off around 25% power in veg. Once the plants get bigger, I'll slowly increase the power.
Mine are around 24 to 32 inches away, but I never raise or lower my plants.

 

[Roy Growin]

It's gonna be trial and error at first, but your plan sounds good

 

[BigBudsBunny]

Those Mars FC 3000 are pretty strong lights. I usually start off around 25% power in veg. Once the plants get bigger, I'll slowly increase the power.
Mine are around 24 to 32 inches away, but I never raise or lower my plants.

damn, I just put a fc 4800 evo in my 3x3 tent for flowering. If the fc 3000 evo is that strong, gonna have to be super careful with that bad boy.

thanks for your input, guess i'll start at 30" and a little power and boost up as the plants react

 

[BigBudsBunny]

started at 27" and about 15% power

 

[Delps8]

I will be transitioning from Metal Halide 400w to a mars hydro fc 3000 evo with the 301h diodes. This is in my 4x4 veg area where there is seedlings, clones, and vegging plants. I keep the canopy even here for vegging and the established clones by using risers and keep seedlings further away. The MH light is approximately 18" from the top of the canopy at 75% power (300w). I was wondering how high I should start the led for transition and at what power level to start at. My guess is I should start them at a set height say 24" or 18" and adjust the dimming as they get acclimated to it rather than raising and lowering the light. - is this the right thought concept?

Plants adjust to markedly changed light levels in a day or two. Per Bugbee, a plant at say, 500µmol can be taken to 700 in one day and then 900 the next. There's simply no need, as far as the plant is concerned, to gradually increase PPFD. Cannabis is a light whore loves light.

In terms of your settings, I'd go with 18" at 50%, and see how they react. Then go to 75% the next day, see how they react. And then go to 100%.

Usually, the recommendations from the manufacturer are pretty good but the hang height and dimmer settings in the graphic below do not match the PPFD map. At 12" above your plants and 75% your plants will be at about 800µmol. That's well within where cannabis will thrive but it might take a few days to get there.

With an LED, as you increase the hang height your PPFD drops but the PPFD map become more even.

Two items - I strongly recommend that growers spend $32 on a Unit-T light meter. Second, growers do far more harm to their crop yields by not turning up their lights than they do by turning their lights up too high.

The reason I state that is that a it's very hard to damage a plant by giving it too much light. I've had my plants get too much light a few times and it's no big deal. In one case, the dimmer on my light failed. I noticed that the temperature of the tent was high and, when I walked into the garage, I could see that something was going on with the light.

The plant was getting 1250µmol so I shut off the light and swapped in another dimmer. A few of the leaves had turned away from the light but, after about 30 minutes, they had rotated back to their normal position.

In contrast, most grower do not get the most out of their grows because they do not give their plants enough light. Roughly speaking, every 50µmol increase in average PPFD will increase yield by about 4%. Below is a table I've created from the cited paper so you can see how yields increase as PPFD increases.

If you check out my grow journals, you'll see my light readings and you can check out the results.

 

[Delps8]

I will be transitioning from Metal Halide 400w to a mars hydro fc 3000 evo with the 301h diodes. This is in my 4x4 veg area where there is seedlings, clones, and vegging plants. I keep the canopy even here for vegging and the established clones by using risers and keep seedlings further away. The MH light is approximately 18" from the top of the canopy at 75% power (300w). I was wondering how high I should start the led for transition and at what power level to start at. My guess is I should start them at a set height say 24" or 18" and adjust the dimming as they get acclimated to it rather than raising and lowering the light. - is this the right thought concept?

I recommend that growers get a light meter. $32 for a Uni-T and it can help you get the most out of your grow.

One reason to do use a light meter is that it can tell you how much light your plants were getting from the MH light. Once you know that number, you can ramp up from there.

A decent alternative approach is to use the settings that the growers recommend. In most cases, they're pretty good.

This is a screenshot from the product page on the Mars site. 400-600µmol is very conservative, in my opinion, but I believe in feeding my plants well and, by about day 40, my plants are at the 800 because, until you reach the light saturation point, crop yield increases, in an almost linear manner, as light levels increase.

 

[BigBudsBunny]

I recommend that growers get a light meter. $32 for a Uni-T and it can help you get the most out of your grow.

One reason to do use a light meter is that it can tell you how much light your plants were getting from the MH light. Once you know that number, you can ramp up from there.

A decent alternative approach is to use the settings that the growers recommend. In most cases, they're pretty good.

This is a screenshot from the product page on the Mars site. 400-600µmol is very conservative, in my opinion, but I believe in feeding my plants well and, by about day 40, my plants are at the 800 because, until you reach the light saturation point, crop yield increases, in an almost linear manner, as light levels increase.

have ordered a uni-t monitor - started a thread about it to help others yesterday to help determine power and distance.
I have the fc 3000 evo (vegging) and the fc 4800 evo (flowering) and both lights show the same info as your attachment. Both lights can't be at the same settings and give the same results which is why I don't trust their documentation and bought the uni-t meter. Furthermore when corresponding with Mars Hydro, I asked for the dimensions of the fc 4800 evo as they differed depending where you looked. They emailed me the dimensions of the light which were wrong. They told me it was approx. 24 x24 and it's actually 32 x 32. So it seems their own documentation is suspect and their sales people don't know their own products. I like the lights/ they seem to be built well. God knows they are bright enough. But their documentation and info provided regarding their use is very suspect. I even found different ppdf charts for the same light at the same distance with vastly different results which prompted my inquiries to them.

Plants adjust to markedly changed light levels in a day or two. Per Bugbee, a plant at say, 500µmol can be taken to 700 in one day and then 900 the next. There's simply no need, as far as the plant is concerned, to gradually increase PPFD. Cannabis is a light whore loves light.

In terms of your settings, I'd go with 18" at 50%, and see how they react. Then go to 75% the next day, see how they react. And then go to 100%.

Usually, the recommendations from the manufacturer are pretty good but the hang height and dimmer settings in the graphic below do not match the PPFD map. At 12" above your plants and 75% your plants will be at about 800µmol. That's well within where cannabis will thrive but it might take a few days to get there.

With an LED, as you increase the hang height your PPFD drops but the PPFD map become more even.

Two items - I strongly recommend that growers spend $32 on a Unit-T light meter. Second, growers do far more harm to their crop yields by not turning up their lights than they do by turning their lights up too high.

The reason I state that is that a it's very hard to damage a plant by giving it too much light. I've had my plants get too much light a few times and it's no big deal. In one case, the dimmer on my light failed. I noticed that the temperature of the tent was high and, when I walked into the garage, I could see that something was going on with the light.

The plant was getting 1250µmol so I shut off the light and swapped in another dimmer. A few of the leaves had turned away from the light but, after about 30 minutes, they had rotated back to their normal position.

In contrast, most grower do not get the most out of their grows because they do not give their plants enough light. Roughly speaking, every 50µmol increase in average PPFD will increase yield by about 4%. Below is a table I've created from the cited paper so you can see how yields increase as PPFD increases.

If you check out my grow journals, you'll see my light readings and you can check out the results.

Thanks for the info. Your experience with these slights compliment what I have been reading about them. I have ordered a meter based on the info I received from Mars Hydro which doesn't seem to be exactly accurate ( see my reply below this). As per your post, I'm just trying to find the right intensity at the right height. Have also read that 800 is the limit for light saturation level of vegging plants. When I get my meter I will get netter dialed in. Am at about 20" now and gonna drop that down to 18" today. My power is at 25 % and have been raising that slowly.

thanks again for sharing your experience - it helps a lot!

BBB

 

[Delps8]

have ordered a uni-t monitor - started a thread about it to help others yesterday to help determine power and distance.
I have the fc 3000 evo (vegging) and the fc 4800 evo (flowering) and both lights show the same info as your attachment. Both lights can't be at the same settings and give the same results which is why I don't trust their documentation and bought the uni-t meter. Furthermore when corresponding with Mars Hydro, I asked for the dimensions of the fc 4800 evo as they differed depending where you looked. They emailed me the dimensions of the light which were wrong. They told me it was approx. 24 x24 and it's actually 32 x 32. So it seems their own documentation is suspect and their sales people don't know their own products. I like the lights/ they seem to be built well. God knows they are bright enough. But their documentation and info provided regarding their use is very suspect. I even found different ppdf charts for the same light at the same distance with vastly different results which prompted my inquiries to them.

Thanks for the info. Your experience with these slights compliment what I have been reading about them. I have ordered a meter based on the info I received from Mars Hydro which doesn't seem to be exactly accurate ( see my reply below this). As per your post, I'm just trying to find the right intensity at the right height. Have also read that 800 is the limit for light saturation level of vegging plants. When I get my meter I will get netter dialed in. Am at about 20" now and gonna drop that down to 18" today. My power is at 25 % and have been raising that slowly.

thanks again for sharing your experience - it helps a lot!

BBB

Glad to heat that. Your efforts will be well rewarded!