Cree CXA analysis

Thats a flexible light system! Kudos!

"This is also the reason why I suspect the CXA3590 might over concentrate the power for a 115 degree beam angle."

Do you mean that you want a wider angle? Or that it's to concentrated to the middle of the angle? How big of an area can you cover properly from 6"?

For example if you were running a CXA3590 at 1050mA, it would dissipate 80W. That is a huge amount of light so you would have to back it away from the canopy, but if you back it off too far a large portion of the light would escape out the sides, requiring the use of a reflector and more vertical height. So that is what I mean that it is too concentrated compared to the CXA3070 at 1400mA 52W which is very concentrated as well. FFH is squeezing 425W in a 3X3 (47W / sq ft!)

Thank you for explaining supra! I love this forum, but sometimes have to struggle a bit to comprehend the language and the lingo.. Gonna se if i find any threads about FFH's grow.

Hi Supra, would it be possible to post how you determine how efficient a LED is (the equation and method, tools involved etc)? as well as a chart of the efficiencys at different MA for the common leds you have tested? (if you have that info)

also can you state if you have measured the lumens or par, or are using those figures from the data sheet.

Thanks alot!! You are very helpfull!

Hello pirg, I calculate the efficiency from the data sheets. I trust Cree, Osram and Bridgelux data to be reasonable accurate and it is very helpful to understand what differences to expect from on bin to another.

For white LEDs we have to rely lumen data and convert to PAR W by using the LER. Sometimes we estimate the LER from the curves (as Mr Flux has done here) for each color temp, and in the case of the Cree 2700K and 3000k we got the LER directly from the manufacturer. So we need to figure out how many lumens are expected at each drive current and junction temp. For this we extrapolate from the manufacturer graphs and charts, adjusting for bin, color temp, temp droop and current droop. Once we have lumens converted into PAR W, we then have to figure out dissipation power at each given current. This changes slightly based on junction temp as well because the Vf shifts downward as junction temp rises.

As you can imagine, this is a good job for a spreadsheet. The tedious part for me is figuring out the current droop factor and Vf at each current. This requires pixel counting


So as an example, lets say we drive a CXA3070 3000K AB bin at 1.4A. If you use sufficient good cooling with a reasonable ambient temp, you might be able to get a Tj of 50C. According to the PDF that is about 7350 lumens using the typical figures. Dissipation will be about 52.2W (1.4A * 37.3 Vf). So that is 140.8 lumens/W. Divided by the LER (325) we get 43.3% efficient or 22.6 PAR W.

Once you have a general idea of the efficiency you are working with, you can make comparisons between white LEDs much better and you can plan for how much cooling will be necessary. But when it comes to significantly different color temps or monochromatics, we cannot make as direct of a comparison. Blue LEDs are the most efficient light sources in the world. Even in the consumer market we can get blue LEDs that run over 60% efficient and cheaply. But blue photons require more energy to be created than reds (PAR W), and photosynthesis is driven by the number of photons (μmol m-2s-1), not by their energy, so the red LEDs gain an advantage that may offset their lower radiant efficiency. Also, blue photons might be somewhat less efficient at driving photosynthesis than reds/deep reds. On top of all that, there are varying photomorphological effects that need to be considered (stretch, trichomes, terpenes, cannabinoids, density, leafiness etc). But at least with the efficiency numbers we have a really good reference point to judge the potential of a light source.

Supra Thanks for your reply. If i wanted to test the efficiency of a chinese led, and had a apogee quantum meter, how do i test it? Where is the measurement done? 1 foot from the source? right at the source? You get a par reading, is that the same as PAR W? Thanks

I think you'll need an integrating sphere to take that measurement. https://en.m.wikipedia.org/wiki/Integrating_sphere

Just guessing, but it's probably a tricky measurement to take without a lot of error.

Maybe there is a way also with a calorimeter. Power in - heat measured = light output? I'm just shooting my mouth off here.

Ya unfortunately the Apogee may not be ideal for warm white LEDs, it seems to be "blind" above 650nm. My lux meter is almost blind to 450nm and 660nm.

The ones i want to check are chinese full spectrum (purple) 90 actual watt units.

Ya the same goes for them and most growing LEDs. I think the "full spectrum" lights claim to have a lot of output above 650nm.

Those meters can only find intensity anyway, not power.

I guess you could estimate by taking the intensity in the middle and using the output distribution pattern to calculate how much power is being emitted.

happy75 said:

Last week I received spectrographs of the Vero 18, 2700K 90 vs 2700K 80 cri and the Vero 18 3000K 80 cri vs 2700K 80 cri. The last one is posted as an image, for those who are interested.

Click to expand...

Could you please also post the second picture of Vero 18, 2700K 90 vs 2700K 80 cri too?