Got my new PAR/PPFD Meter ... need advice on readings!

Hej!


Today my Apogee MQ-200 Quantum Meter finally arrived.

I am completely new to LED and just installed a room with 24 Cree CXB3590 running @50W each with Meanwell Driver ELG-150 (8 pcs). Its a 1 COB per sqft Layout.

Now - I really need help which readings I should get @ plant-canopy using my PAR Meter. Basically I need to tweak distance or dimm my COBS down - if possible.


Which distance are you growing your plants from your CREE`s @50W?
Should I keep them running @50W each and just adjust the height according to the plants growth?


I would be very grateful for informations both for Veg (18/12) and Bloom (12/12).
I am readings everything between 700 and 1100 PPFD on plant canopy ... really getting confused


Thank You!!!

peregrines said:

Which distance are you growing your plants from your CREE`s @50W?

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18"-24" growth
12"-18" blooming

I run my 300 watt Cree light @ 16" and dimmed to 180 watts for veg.. @16" and 300 watts for flower..

Trick question!

there is no perfect PPFD!

it depends on a dozen factors including plant size, health, genetics, temperature, humidity, spectrum, water, nutes, photoperiod, etc etc

24 hour veg 300-700 ppfd
18 hour veg 400-900 ppfd
12 hour flowering 600-1500 ppfd

if its your first cobs "less is more" and will still yield great results

50W/SF of cobs is a shitload of light (dont confuse 50W/SF with 50W/cob, the latter is semi irrelevant as long as your plants arent super close like 6")

I would try to keep your canopy 18-24" away or dim them. the good news being with that massive array they should work phenomenally at that distance with excellent canopy penetration

The height of the fixture is determined by the uniformity of light distribution. You will see the PPFD vary over the whole surface, but you start by calculating an average of your measurements. Either from a matrix across the whole surface, or do a quarter of the surface, or perhaps even a diagonal. Either way, get an average. Then the darkest spots in your room should receive at least 80% of that average.

Once you get that corrected, the height is set. If you want to reduce the amount of light, you use the dimmer. The light uniformity will remain correct.

You then use the average you measured and dim it down to whatever number you want. Anywhere between 250 ppfd to 1500ppfd could work, but I wouldn;t go much over 800ppfd especially in a first run.

I personally ended up at 12" distance for uniformity, but that's with 0.8 COBs per sqft. With 1 COB per sqft you can probably go lower even. Unless, if you put 90 degree reflectors on the COBs then you will need to about double the distance.

You are the best!
Thank you so much for this great bit of information!!!

I didnt know "less is more" and the fact I have to be careful at all! I always thought "the more the better" - at least regarding the amount of light my plants get.
I am going to carefully follow your advice and hopefully have success with COB.

Thank you Guys!

peregrines said:

I didnt know "less is more" and the fact I have to be careful at all! I always thought "the more the better" - at least regarding the amount of light my plants get.

Click to expand...

too much light will stress the heck out of a plant, esp small ones

The apogee 120 sensor does not accurately measure leds, you need the 500 sensor. Add 20+ percent to your par readings for closer to accurate numbers when measuring cobs.

Here is a video on the different sensor, here is where they start talking about the ranges they measure, as you can see the 120 drops off early compared to the li cor and the apogee 500 sensor

Thank You linky & Cobkits for your advice!!

Especially if my Meter is reading 20% less!!!? I got the Apogee MQ-200 Quantum Meter - which is kind of expensive to me - to get accurate readings and everybody seemed to recommend it to me .... now I am kind of disappointed its not providing accurate readings with LED.
Today I measured 1050 PPF on my plant tops ( they just started 12/12) with peaks around 1150 PPF and lows around the walk-side around 850.
If I add 20% I think I am already in a "risk-zone". Adding above mentioned 20% to 1150 that would add to 1380 PPF
Think I am going to reduce wattage from 50W per Cob to 40W at least for the first 1-2 weeks blooming.

its not awful with whites, its more off on mono (red/blue) cobs)

just watch your plants. 1150 ppfd is still a lot of light