LED Spectral Analysis: Cree, Rebel, larger Bridgelux, a few "chinese" LEDs

K+ for the results! Great read!

 

Look for the Satistronics LEDs.

I don't know if Satistronics still exists other than on Ebay, they used to have an online store at Satistronics Store, China Electronic Components Online Store - Wholesale Development Tools and Components from China but I cannot get it to come up anymore (which is fine with me, they are NOTORIOUS for bad data sheets).


For what it's worth, I've seen these "bridgelux" LEDs from Aquastyle and similar places and I cannot see one lick of difference between them and all the other chinese ebay specials. I'm not saying they are the same thing but the use of the term "bridgelux" is cheapening the genuine company Bridgelux which produces some of the nicest color white LEDs you can find.

Aquastyle says they are using bridgelux emitters on the LEDs, and Bridgelux themselves has admitted that they might actually be true Bridgelux emitters on these.



I will say this. The PAR output of the chinese LED that I tested was pretty low. I don't have hard data handy, but I've seen with my own eyes where the Cree XML puts out easily double the PAR at the same current of the Satistronics 3w LED, and the Cree XPG nearly does the same thing.

 

Very cool LED data. You mentioned converting the results to something useful. Can you convert the data to tabular format? If so, you should be able to calculate the relative intensity. From there, if you know the PAR, from a meter, such as the apogee, you can convert to total relative intensities to proportion of the total ppfd output. Technically the Apogee meter, underestimates blue/violet and far red, but if you have the response curve of the meter, that is an easy calibration, as you have the spectral data.

This thread discusses the response curve of the apogee PAR meter for example, you could use a similar method.
The PAR Estimation examined, Lighting Spectrum and HEV thread

 

When you say "tabular format", are you suggesting the raw data? If so, I still have the spreadsheets (Excel format) of them all. There are 1 or 2 thousand scatter plots for every line, it's a dixie-normous amount of data for each graph. I had to hand-make the rainbow effect to get it right in the "fill plot line" part.

BTW great thread you linked me to, I bookmarked it.


I've always suspected that PAR meters underestimated the light from LEDs.



One thing I would like to know, and I hope someone can chime in. Some LED drivers use a PWM signal to drive the LEDs (very rapid duty cycle on/off that our eyes supposedly can't detect). I suspect, for photosynthetic purposes, that this is just fine, but I wonder if the PAR meter ends up giving different readings at any given current (say, 700mA) when compared to an LED on a driver that just uses normal analog DC current (at, say, 700mA) where there is no on/off duty cycle.

Make sense? Would the duty cycle mess with the PAR meter?

 

You probably have fractions of a nm? I would think dropping the fractions and using the integer wavelength values would be sufficient.

Yeah, it is interesting how much the PAR meter may underestimate all aquarium lights. Out of the lights tested, the XM 10K actually may be the most underestimated I guess. Personally, I would have guessed the higher K bulbs and LEDs, etc.. would have been the most underestimated.

Maybe, I'm not sure what the update time of the meter is. That would be an interesting question to ask Apogee. Although, I'd think, if slow, the PAR would be the average of the peaks and troughs though, over the update time. Which would also, be the average light available for photosynthesis. So, I'm not sure it would actually matter. Another thought, is that the PAR will be the sum of the par from all the LEDs, where they overlap and the output from an LED should drop off in a fairly Gaussian manner. So, there would be a bit of a polkadot patter, if you will. So, moving the par meter just a bit, could change the PAR, more (up or down, depending on where you move it) than with a halide or a T-5, which would drop off more steadily.

 

None of the drivers used in aquariums use PWM do drive the LEDs. Some use PWM inputs to controls the dimmer. But all use voltage modulation on the LEDs themselves.

 

Yes, some of the definitely do have a pwm output (I'm not confusing the pwm dimmer circuit, I own a couple of the pwm-dimmed Meanwells).

My understanding was that Buckpucks had a pwm output but I can't say for sure, but I do know the Nano-Box driver is a pwm output. I've used it myself. It's a neat driver but on very large LEDs, you can actually "sense" the pwm on lower current levels.

The Nano-box driver is from this place: Products - Nano Box Reef



There are a bunch of common chinese LED drivers that flashlight and bike-light modders often use that are pwm as well, and I've seen (and used) them over aquariums before. Granted, these are not nearly as common.

 

Yes, the data sheet has, if I recall correctly, down to the hundredth of a nm.

I'd be glad to email you a couple of the more common combos (or individual LEDs) if you'd like to give this a shot.

 

I can see if I can confirm what the numbers mean. Presumably, they are some sort of intensity value. So, if you wanted to convert to relative intensity, for a given graph, it is as simple as finding the maximum value for the graph (usually Excel or whatever program your working in would have a MAX() function), then divide all the values by the max and multiply by 100. This gives the relative percent for any given data-point.

If you wanted to standardize over all the graphs, you'd have to make sure that the intensity value is fixed and does not vary based on the some other factor, or setting. I could look into this. If so, then you could standardize all the graphs to each other. You would just find the max value out of all of the data and divide all of the values by that number, and multiply by 100. This would let you compare intensities over all of the combination.

Thinking about it again, I'm not actually sure you need to convert to ppfd values. These might not actually be that useful. I was thinking, you could use these to scale the configurations, to larger arrays, but that wouldn't work because it wouldn't take into account the LED spacing on the arrays, and coverage area. So, your probably better off just sticking to simple relative intensities.

 

I'd be glad to provide you with all the data from the graphs if you'd like to do this. I'm not able to spend the time on it right now because of my responsibilities as a grad student and family man . It sounds quite interesting.

Actually, there is a guy called "Hoppy" on The Planted Tank Forum that is quite good at calculating approximate PAR values even if given PAR levels for a single LED. He's done it for years with T5's and T12's and recently started messing with LEDs. His background is apparently such that this sort of calculation common to him.