Help interpreting LUX meter results for 500w CMH

[tri.helix]

I'm hoping someone can help me figure out what I'm missing with the results from my LUX meter.

I have a 500W CMH (single bulb) fixture with brand new 3000k bulb. It's currently 2 feet away from the canopy, which is as close as I can get it. If I get it any closer the plants start to show signs of light stress and heat stress.

From what I understand, I should be aiming for around 50,000 LUX, but I'm only reading about half that at 2ft distance from light center.

• Is my bulb shit?
• Do I need more air conditioning or an aircooled fixture to get the bulb closer?
• Am I screwing up my LUX measurement?

Thank you for any suggestions.

 

[Koondense]

What values are you getting under the clear sunshine?
Could be in need of calibration.


Cheers

 

[tri.helix]

What values are you getting under the clear sunshine?
Could be in need of calibration.

Thanks for the suggestion, I took it out into the sun today and it was averaging around 100,000 LUX. I guess this points to my bulb?

 

[Koondense]

Yes, very likely.

Honestly i never heard of a 500w cmh bulb, only 315w and multiplied.
What is the highest value from the bulb, like from less than 10cm distance?



Cheers

 

[tri.helix]

Yes, very likely.
Honestly i never heard of a 500w cmh bulb, only 315w and multiplied.
What is the highest value from the bulb, like from less than 10cm distance?

Here is the fixture and bulb that I'm using.

at ~10cm from the bulb my meter maxes out, if I pull back to about 15cm I get about 190,000 LUK.

I dropped my bulb a bit lower, closest plant canopy is 13" from the bulb and is now reading 39,000 LUX (which still doesn't seem like enough).

 

[troutman]

Make sure the temp isn't too high.

 

[I'mback]

There is a lot of stuff you are omitting here good buddy. What is the size of your room? What type of ventilation is in there? What is the size of your exhaust fan? What kinda temps are you seeing with lights on, off? How far along are your plants? 50000K is a good number to shoot at for later stages of flower.

The formula for converting Lux to PPFD (umol) is Lux X 0.0185 or PPFD X 54 = Lux

PAR (umol) readings at various stages as follows:

• seedlings ~ 60-90 umol, (3240-4860 Lux);
• clones ~ 100-200 umol, (5400-10800 Lux);
• veg~ 300-425 umol, (16200-22950 Lux); and
• flower 700-1200 umol. (37800-64800 Lux)

Anything over 1000 umol requires CO2 augmentation. FWIW, I pretty much grow IAW the aforementioned numbers and, I keep my readings for flowering around 950 umol, close enough to 50000 Lux. Of course these setting are all gradual. Hope this helps

 

[f-e]

The formula uses a factor of 54 for sunlight. A cmh could be 65. I have no problem with 400umol at the edges, growing 9" buds of good weight. That might only be 60% of a perfect co2 grow, but still produces diaries with a wow factor. It's also hps umol, which arguably isn't as good as cmh sourced umol.

22000 is the meter saying? divide by 65, 338umol. An old skool 250mh could do that. I have seen similar meters to the one in your hand with switchable scales of x20 x200 which would be 44,000 lux, but then you got almost full on equatorial mid day readings outside. So I don't see scaling being the answer. Some meters don't measure the full par range, and may in reality use a portion of the red or more commonly green part of the spectrum. Presuming to itself, that all other colours will be as bright. But if it's looking at green, and your lamp dips in the green spectrum, it will give a dipped reading.


edit: I would start with a plug in power monitor, to see what power the light is taking from the wall.

 

[I'mback]

The formula uses a factor of 54 for sunlight. A cmh could be 65. I have no problem with 400umol at the edges, growing 9" buds of good weight. That might only be 60% of a perfect co2 grow, but still produces diaries with a wow factor. It's also hps umol, which arguably isn't as good as cmh sourced umol.

22000 is the meter saying? divide by 65, 338umol. An old skool 250mh could do that. I have seen similar meters to the one in your hand with switchable scales of x20 x200 which would be 44,000 lux, but then you got almost full on equatorial mid day readings outside. So I don't see scaling being the answer. Some meters don't measure the full par range, and may in reality use a portion of the red or more commonly green part of the spectrum. Presuming to itself, that all other colours will be as bright. But if it's looking at green, and your lamp dips in the green spectrum, it will give a dipped reading.


edit: I would start with a plug in power monitor, to see what power the light is taking from the wall.

Don't want to but old school it is. I know how the LEDs are being marketed (unfortunately) by equivalent to. Neither is comparable. That is not the factor that determines efficiency @ 1/3 the price

 

[tri.helix]

Make sure the temp isn't too high.

Would that have an effect on how the meter picks up LUX levels, or is this related to the heat stress if I move the light any closer?

There is a lot of stuff you are omitting here good buddy. What is the size of your room? What type of ventilation is in there? What is the size of your exhaust fan? What kinda temps are you seeing with lights on, off? How far along are your plants?

Thank you for all the info, I have no CO2 supplementation so it sounds like I might not be as far out of the suggested range as I had thought. Here are more details:

• Size: 4x4x8 tent
• Ventilation: passive intake
• Exhaust: 6" AC Infiinity inline sucking through 6" carbon filter and blowing out of the tent. It's triggered by humidity/temp set points so the airflow is not always consistent.
• Average daytime temp: 78F
• Average daytime humidity: 55%
• Average nighttime temp: 64F
• Average nightime humidity: 50%
• VPD: I use a controller to adjust humidity based on temp to keep VPD within 1.0-1.6KPA
• Age: Most plants in the tent are in the last couple weeks of flowering, there are a few smaller plants in ~week 2 of veg.

I would start with a plug in power monitor, to see what power the light is taking from the wall.

Thank you for walking me through the calculation, I wasn't aware the factor should be adjusted to 65 for CMH. I like where you're going with this, I just ordered a power meter to confirm it's actually pulling 500W.

 

[I'mback]

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