So my first attempt at growing with a CMH/LEC I nearly lost my whole crop. With in 2 weeks of sending into flower I had all sort of deficiencies showing and at 4 weeks decided to flush as plants had locked and switched back to a HPS. Ended up helping alot but my yield was still affected. I came to the conclusion I under estimated the power of the CMH and over worked the plants as the pots were drying pretty quick and the top leaves were yellowing. I'm on my second attempt now and im still not conviced I'm using them right. Here's where I'm confused. I have a 1.5 x 1.5 tent on one side I have my 315 Phillips 3100k bulb and on the other side I just added a 600w HPS and set it to 400w on the ballest as not introduce to much light at once. When I measure with my lux meter the HPS is giving off about 40,000 lux and the CMH is only hitting about 20,000 lux, they are both at exactly the same hight above the canopy(about 2 feet). From what I learned a 315CMH is meant to be compared to a 600 HPS. I'm so lost. Can someone please shed some light on this(no pun intended). Thank you in advance.
Correct.
Rocket Soul
Well-Known Member
If youre deficiencies started out with Calcium or magnesium, imobile nutrients, then it can have to do with differing transpiration rates: HPS heats the plants leaves more which makes it lose more water to transpiration, the water and nutes left in the plants get more concentrated. If your CMH side isnt transpiring at the same rate it wont uptake as much water and nutes which can lead to deficiencies. Im by no way an expert but this seems to have been the problem when the grow im consulting for changed from hps to cmh. But please let everyone chime in before you change anything.
Kushash
Well-Known Member
calcium is immobile. Magnesium is mobile.
Rocket Soul
Well-Known Member
Cool, thx, i didnt know
nfhiggs
Well-Known Member
That is a little odd - the CMH should read higher lux, because its a more green-centric light source and Lux is a green-centric metric.
nfhiggs
Well-Known Member
Wow - I didn't realize the lm/W efficiency was that much lower with the CMH
Rocket Soul
Well-Known Member
Yes, but its 1.95 ppf/w, so 100 lux of cmh contains almost the same amount of photons as 200lux of hps.
wietefras
Well-Known Member
A double ended HPS outputs 2.1ppf/W
The conversion rate from lux to ppfd for CMH is 64 and for HPS 78. So 120 lux of HPS would be equivalent to 100lux of CMH.
There is an insane amount of hype and nonsense going on in the CMH camp.
I'll bet that if you replace a singled ended 400W HPS with a $10 reflector (that's been used for years), by an expensive 315W CMH fixture with the latest MIRO reflector hood, that you will see an increase in yield from the new fixture. However that's not because if CMH being such a great light, but because 50% of the HPS light was wasted on that poor reflector (and walls due to poor reflection).
Randomblame
Well-Known Member
I would measure the leaf temps and humidity under both lights. On the HPS side it should be around 27-28°C with 25°C ambient. Do you get the same readings on the LEC side?
These yellowing of the upper leaves can have two reasons(of course more, but these are the most likely),
over-saturation(probably not with 20klx) or to low humidity(VPD too high, most probably).
I could imagine, the latter is the case and when you increase the humidity by 10% or so the symptoms will disappear. Try it with 55-60% and see if it helps..
Pics would also help a lot to identify what's going on...
These yellowing of the upper leaves can have two reasons(of course more, but these are the most likely),
over-saturation(probably not with 20klx) or to low humidity(VPD too high, most probably).
I could imagine, the latter is the case and when you increase the humidity by 10% or so the symptoms will disappear. Try it with 55-60% and see if it helps..
Pics would also help a lot to identify what's going on...
The humidity is around 60%. I raised the lights a bit and it seems to be better but after getting some run off I'm pretty sure I had slight lockout so just feeding water now. Still trying to work out if the cmh is over working or under working them.
So could I adjust my cmh so it reads 30,000 lux if I'm trying to achieve the same intensity as 60,000 lux from a HPS ?