PAR Quantum Light Meter - LED vs. HPS - Cold start flux output vs. Running

DaveTheNewbie said:

some bad engrish that may be of interest :

Click to expand...

Yes, good info and true - but could also be a bad excuse from the lamp manufacturer to buy cheap 3 grade LEDs (Bin's)
or cut down on cooling to save $.

A example maybe is this lamp
http://www.ebay.co.uk/itm/120W-LED-Hydroponics-Plant-Grow-Light-Red-Blue-0011-120W-Ship-from-UK-/221005251404?pt=UK_HomeGarden_Garden_PlantsSeedsBulbs_JN&hash=item3374f0834c

Much cheaper than my 120W, but if I look at the LED pcb it looks like the LED's are mounted on top of the pbs
and not like on my lamp, where the LED's flat bottom is mounted directly on the head sink.

This pcb type is ok for highpower LED's I think.
The heatsink behind the pcb in taken the heat.



This is not.
The pcb is the heatsink or it's mounted on a heatsink( acting as a extra layer of insulation in my book - could be mistaken)




Don't know if you have seen the thread: Lighthouse Hydro is doing it wrong.
but it's worth a quick scan if the subject is cooling, temperature vs flux output and lifespan.

I decided that I would test the difference in PAR value, between a blue and a red LED
now that I was in control of the intensity. Measuring under normal running conditions
had not been possible for if I put the PAR meter up close to a single LED it would overload.

LED module on my desk :


Increasing the voltage:


Until the PAR meter was measuring 1000 uMol under the blue LED


And then moving it over to a red LED


Thinking back to the PAR meter sensitivity spectrum from the manual this was surprising.


Now it's difficult to tell whats behind this, and if under powering the LED is a valid way of testing them
I don't know - no charts and no way to tell how a red vs. blue is behaving with the measured voltage.
unless you unsolder them and measure amps.

With the module supplied with 29,47 volt the following was measured over the single LEDs:
Red = 1.77V
Blue = 2.55V
UV = 2.84V
IR = 1.28V
It's from one of the six corner modules with add on.

For the module to draw 710mA it has to be supplied with 36.4 volt it seams,(hence the 3 12V PSU's connected in series)

It's impossible to measure the voltage over individual LEDs while running a current of 700mA,
doing that without the LED being hold tight to the heatsink but floating freely in the air
they properly last 10 sec.

And I still wonder if it such a great idea to mix LED colors in the same series connection,
when the LED's has different voltage needs.

But I for sure had expected the reversed result with that sensitivity curve.

Edit: I also tested all the red LED's in the module for deviation in output flux, and it's was from 630-680.

Really excellent stuff here.

would love to see some comparative measurements of PAR T5 setups.

Wow this is some very good information.

Allow me to comment: I would not say that main-stream LED is more efficient than HPS.

How much surface does one LED cover when it produces 1000 umol and is that uniform? It is really hard to measure the PPF by doing a PPFD measurement. You could try to do an integration of many points on the surface, because just measuring under the lamp will not tell you anything about the efficiency of a lamp.

a 1000W HPS lamp can light 2 square meters with 1000 umol s-1 m-2. The PPF of that lamp is over 2000 umol s-1.

If you want to do a reverse calculation you need to measure with many points on a surface in a darkroom and integrate. Of course a 250W lamp is not a good comparison, and specifically not the 250W MH which is more than twice as inefficient (in output per watt) as a 1000 W HPS lamp. The reflector plays a role in the measurement too. You can't compare a directed LED to a HPS without reflector, and then which reflector?

Even if the output per watt of main-stream LED would be a bit more than the HPS it is a hell of an investment to replace 1000W HPS by LED - imho quite a compelling investment advantage for the HPS. LED is a great technical solution but no magic bullet.

A li-cor quantum meter is a really good investment too btw!

Hi all. I was a grower for years but took a pause during some life upheavals that I had to sort out. I'm looking to get back into it and I'm really interested in the recent advances in LED grow-lamps and these quantum meters! I notice that a lot of testing seems to be done directly underneath the lamps. Has anyone done a light-spread (and/or depth) test between a HPS and a comparative wattage LED lamps to see which gives the best results at the edges of the garden and how far down the light penetrates?

thanks rasser,

I think your meter is fine, but should be done comparing led to led.. there more in the spectrum then the LED vs. HPS. but hell I would test everything. haha

it's like having a PPM meter, as long as you have a base number to go off, that's all you need. doesn't matter the reading if you read the plant, and adjust from there. obviously the li-cor is used most common in plant studies, but as I said your meter works if you use the base number and compare to that.



for your comment on voltage needs, it doesn't matter, you can hook different voltage together. not sure I can say that on parallel strings though as I don't know..



that PAR meter info , expanded info is here for anyone.

dont know if this have any interest ?

but my 120x3W (288 actual watt) customized LED panel almost produce the same foot candles as my old 600W HPS light



both grow nice Buds tho




IMO the LED grow a bit smaller but more compact/potent Buds then the HPS did, with half the power used, but also half the ground covered (found 18 inch`s is best distance, 12-15 is to close)


bare min mening og erfaring med LED/HPS