Light spectrum question

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robob02

Active Member
I was vegging under a standard 400W HPS lamp. I recently purchased a 5000K metal halide conversion bulb and started usnig that for vegging. Under the new light it seems the plants have more stretch - the internode spacing has increased and the plants don't seem as bushy.

Im wondering if this has something to do with the spectrum of the new light or is this normal? I did read something about photosynthisis absorbtion is greatest above 5500k. The HPS was 45, 000 lumens while the MH is 36, 000. Is that the issue? Should I just go back to the HPS?

Thanks!!
 
bicycle racer

bicycle racer

Well-Known Member
try to keep your light no more tha 18 inches from your plants or as close as 6 inches if it is an open fixture. the halide has a better spectrum for veg but lumens are lost as you said so get it as close to your plants as you can without cooking them. with halide you should be getting bushier growth.
 
la9

la9

Well-Known Member
lozac123 said:
yeh, distance is the key.
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Distance is definitely the key. With MH I had to keep the light so close to the plants the coverage sucked.

I got better results with 4 foot flourescents so that is what I'm sticking with now. If you are wondering, I also get better results with 4 foot flourescents over CFL's. I also got better results with Gro Lux bulbs over cool white.
 
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robob02

Active Member
mygirls said:
how close is your light to the plants.
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I do have the light closer than I did under the HPS. Its probably about 10" from the tops. The MH does seem cooler than the HPS, maybe I could go closer...but then coverage is lost...

Thanks
 
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robob02

Active Member
bicycle racer said:
try to keep your light no more tha 18 inches from your plants or as close as 6 inches if it is an open fixture. the halide has a better spectrum for veg but lumens are lost as you said so get it as close to your plants as you can without cooking them. with halide you should be getting bushier growth.
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I have the light at about 10" from the tops, I could try a little closer I guess. The plants actually seemed more bushy under the HPS. I thought getting the MH was going to make them really bushy, but its starting to seem like my plan back fired.

thanks
 
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robob02

Active Member
la9 said:
Distance is definitely the key. With MH I had to keep the light so close to the plants the coverage sucked.

I got better results with 4 foot flourescents so that is what I'm sticking with now. If you are wondering, I also get better results with 4 foot flourescents over CFL's. I also got better results with Gro Lux bulbs over cool white.
Click to expand...
This sounds like an interesting plan. How does this work for taller plants? With florescenta the top of the plant would get lots of light but output would be lost for the lower branches. Do you do Sog or Scrog orLST to keep the canopy even?

Thanks!
 
la9

la9

Well-Known Member
robob02 said:
This sounds like an interesting plan. How does this work for taller plants? With florescenta the top of the plant would get lots of light but output would be lost for the lower branches. Do you do Sog or Scrog orLST to keep the canopy even?

Thanks!
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I just use the 4 footers to veg, 4 bulbs seems to give the plant all the light it needs after all they are only going to be 2 foot tall before flower. The plants just seem to get exactly what they need.

After Veg I switch to HPS and then it's off to the races.

I didn't like the MH results I got even though it's supposed to be best to use. It seems you experienced the same thing I did so it's not a coincidence.

On a side note, I am going to try LST this time around and see what happens.
 
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frmrboi

Well-Known Member
robob02 said:
It's tough to find a 6500K in a conversion bulb.
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no, it's impossible actually. You have to have a MH ballast if you want that color light in HID. Florescent is the way to go as the plants are small anyways unless your a commercial grower with hundreds of clones.
I like the CFLs for vegging myself.
 
bicycle racer

bicycle racer

Well-Known Member
they make all kinds of different kelvin ratings for mh conversion bulbs you just have to google around. personaly i use thin fluoros t-5 or t-8s i forget but they work well for veg.
 
bicycle racer

bicycle racer

Well-Known Member
i have a conversion bulb that has a good k rating ill have to dig it up to see what its rated at its in storage. the cool thing about conversion bulbs is if im correct they have more lumens per watts than a metal halide ballast does of the same watts.
 
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robob02

Active Member
la9 said:
I just use the 4 footers to veg, 4 bulbs seems to give the plant all the light it needs after all they are only going to be 2 foot tall before flower. The plants just seem to get exactly what they need.

After Veg I switch to HPS and then it's off to the races.

I didn't like the MH results I got even though it's supposed to be best to use. It seems you experienced the same thing I did so it's not a coincidence.

On a side note, I am going to try LST this time around and see what happens.
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I'm trying to cover about a 4'x4' area with ym 400w during veg, what kind of area to you cover with the 4 grow tubes?

Yeah, I'm giving LST a try this time, but the MH is making it stretch.
 
R

robob02

Active Member
frmrboi said:
no, it's impossible actually. You have to have a MH ballast if you want that color light in HID. Florescent is the way to go as the plants are small anyways unless your a commercial grower with hundreds of clones.
I like the CFLs for vegging myself.
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The grow shop by me has a Solar Max thats 7200K and a Sunmaster thats 4000K. From reading, the Sloar Max sounds promising, but according to the chlorphyll chart, its not much (if any) then the HPS.

What type of CFL setup do you use?
 
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robob02

Active Member
bicycle racer said:
i have a conversion bulb that has a good k rating ill have to dig it up to see what its rated at its in storage. the cool thing about conversion bulbs is if im correct they have more lumens per watts than a metal halide ballast does of the same watts.
Click to expand...
Thanks for this, I would be very interested.
 
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robob02

Active Member
frmrboi said:
Sunmaster makes a 6000K, that wouldn't be too far off the mark.
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I'll look and see if I can find this one. How the 5000K is performing has me worried about getting another MH bulb. Maybe just add a 150W of CFL at 6500K to my HPS.

I took the MH out for now and put the HPS back, the stretch was too much to watch....
 
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