Mine are spaced 3 inches apart, which makes a big difference.
I used Cindirella software to build a geometry of the light with 2 and 3 inches apart. Used a depth of 22 inches.
With 3 inches apart the overall intersection on more than 50% light output area is about 73 inches. The hot spots overlap at 7.8 degrees.
With 2 inches the total intersection is 74.2 inches and host spots overal
at 5.2 degees.
In the first case the second led add to the first one around 95-96% of its insensiti.
In the second case the second led add to the first one around 98-98% of its insensitity.
The third led difference between 2 and 3 inches apart also is around 4-5%. So, overall light intensity with 2 inches apart is not 50% more than with 3 inches. Still, something else is here. That why i need the measurement from one led.
No, Tom posted his comparison on his blog, http://www.barrreport.com/forumdispl.../1-Barr-Report
as I recall. And, as I understand it, plants use all of the light within the range of the photosynthetic active spectra, so a high PAR is a high PAR, what ever the spectral distribution of the light. Obviously no PAR meter has a flat response curve for the whole range of light it measures, but it is close enough.
The only post from him about the issure i found on that forum was the link to the Dana's comparison, not his personal.
Here it is:
I am afraid you mistunderstood the PAR. Plants (all plants in general) use all PAR range of spectrum, however, the sensitivity and usable range is specific for each plant. There is so called PUR which is actually unmeasurable without multimillion lab equipment and months (if not years) of research for species. But it is already known, that plants can do very well pretty much without any GREEN and YELLOW spectrum. Green is for sure not used because you see the green leaves, so, all the green is reflected back is not used. Yellow is there too, if you split the spectrum you'll see a lot of it. All this is already experimentally confirmed. Guys at ISS grow salad with only blues and red leds and the salad is yami
So, as you see the sensitivity of plant to PAR spectrum is absolutelly not flat. Blues and reds have a lot more priority than everything else. However, if you look at the apogee quantum meter response curve (can't say anything about LiCor because i did not find their datasheet for the sensor) here http://www.apogee-inst.com/manuals/M..._300manual.pdf
you will see that sensor has pretty much the same respone in 470-600 nm range (green yellow) comparing to more important blues and reds while the real plant are considerably less sensitive in the range of 470-600. So, as i said, point your par meter at a bright green light and you will get high PAR reading which mean nothing to a real plant. Plant eventually will die under that light. It is also have been shown in experiments.
And just for some extra info (the first thing i found):
I'm not sure what you are asking here. I do have data on a single one watt LED, but not on a Cree 3 watt one. I am pretty certain the data will be about the same for the higher wattage LED. I use that data to figure out what PAR I can get with various spacings of LEDs.
Okay. i would appriciate it if you gave me the data. Maybe it will help.
I am basically asking to point a 3W cree led directly to a par meter at any distance and any current and tell me the readings and do the same at some different distance.