Do LEDs color shift when dimmed?

Bilk

Bilk

New member
I have two Ecoxotic Cannons over the tank and right now, have them dimmed to 40% at peak and ramp up from 10% when them come on. Just wondering if LEDs hold true color temps when they're dimmed beyond a certain point. They're rated at 12k. Is this consistent along the power input or is that when they're firing at 100%?
 
If the ecoxotic chips consist only of the 12k white led (a blue led with a phosphor coating), then no matter what dim value you have, the spectral plot is the same...but intensity varies.

Now, if their multichip consists of rgb leds, which Im pretty sure they dont, then yeah you would see a shift, but from what it says in this study, that doesn't seem to be that drastic. But even then, I'm not settled on what exactly is causing the "shift" to the right of their data points. I would feel a lot better if they did individual colors and mapped them out.
 
Aqualund said:
If the ecoxotic chips consist only of the 12k white led (a blue led with a phosphor coating), then no matter what dim value you have, the spectral plot is the same...but intensity varies.

Now, if their multichip consists of rgb leds, which Im pretty sure they dont, then yeah you would see a shift, but from what it says in this study, that doesn't seem to be that drastic. But even then, I'm not settled on what exactly is causing the "shift" to the right of their data points. I would feel a lot better if they did individual colors and mapped them out.
Click to expand...
I really don't know the makeup of the multi chip. I guess that's what I need to look at. I didn't dig into the paper yet and some of it is probably above my pay grade :)

I'm looking into this because I was running them higher and the corals were responding ok. Then I reduced the intensity for fear, in the longer run, they would bleach or respond negatively, from various anecdotal reports of others. Now, at a lower intensity, they do seem to be responding negatively - some are not producing polyps during lighted hours as they did prior. The water parameters are the same as they were before. Nothing terrible is happening, but I want to be cautious.
 
Well then I would think that the lower par level is what is causing the negative effects. Maybe get a par meter and check to see what you're getting? Most sps will do best at around 250 and above. That's an over generalization....but still a good benchmark to shoot for.
 
Aqualund said:
Well then I would think that the lower par level is what is causing the negative effects. Maybe get a par meter and check to see what you're getting? Most sps will do best at around 250 and above. That's an over generalization....but still a good benchmark to shoot for.
Click to expand...
I guess that's probably a worthwhile expenditure. Any suggestions on which is worthwhile and meant for reading LED intensity? I understand reading LED is much different than reading incandescent light sources.
 
There's a lot of debate on which gives more accurate measurements for particular frequencies. However, there really is no debate that they can all get you in the right ballpark. The apogee par meter is a good start...they get a bit more expensive thereafter.
 
Thanks Aqualund. Is there a specific model and probe that I should look for? Also, any recommendations on how to take the measurements? Or is it just stick the probe under the lights in the tank and take the reading?
 
mcgyvr said:
A par meter won't tell you if there is a spectrum shift..
Click to expand...
Ok I guess I didn't imagine it would. In the OP I was asking if reducing the intensity would chromatically shift the LED output - i.e. from 12k to something like 8k. I guess that paper I linked to suggests it does occur depending upon the makeup of the chip.

At this point my goal is to see where the tank stands in terms of overall light intensity as the fixtures are ramped to different levels. Visually judging that probably isn't the best way to go about it. At least par meters don't expire or need regents replaced :)
 
mcgyvr said:
A par meter won't tell you if there is a spectrum shift..
Click to expand...

I guess I should have been more clear. A lot of people have been debating the accuracy of some par meters, with regard to whether they are reflecting the actual par...because some frequencies are not reading accurately.
 
The LED's do not color shift (appreciably) when they dim because they are not really dimming. You see them dimming but they are actually flashing on and off at a rate faster than your eyes can react to.

The dimming effect is controlled through a technique called pulse width modulation (PWM). The power signal is box shaped rather than sinusoidal. When the LED is on 100%, it gets full voltage for the whole duration of the duty cycle (a single time element of when the LED is on and off) . When it is off, it gets zero voltage (obviously). The dimming effect is produced by the amount of time that they are on versus the time that they are off. When the LED is dimmed 50%, it is on for half of the duty cycle and off for the other half.
 
Last edited:
Reef Noob said:
I didn't see any bad data in that study.
Click to expand...
The LED's do not color shift (appreciably) when they dim because they are not really dimming.
Click to expand...

But the data show shift, and even in our discussions at the beginning of the thread, we recognized that it's not much, but there is a shift, because of the data presented by the study.

So, you say you didnt see any bad data, but the data says there is a small shift, but you further say the led's do not color shift?

Seems contradictory to me.
 
I have an interesting set of data from sps under cannon LEDs in a large tank. Multiple mini colonies of several different species at different depths/par readings. Basicaly around 100-175 par, apogee meeter, with 50/50 10k and 454 led cannons was the sweet spot for most sps. Up to 225 things still did good but looked a bit bleached, from there up things started to look very bleached. The most interesting thing was at 300 par the top of the colonies was so white it looked dead but the under side was very colorful and they were growing, but horizontally. Also the most colorful sps was far from the lights, at 80-100 par. Ended up re aiming some lights and dimming to about 80%. haven't seen the tank in 4 months but I hear it's color is better. Should see the tank again in a few months and take more readings. Also leathers like xenia and sinularia did good at all levels, 200par was the highest they were at. Chalices at 80-120 were doing bad, goniapora a bit pale at 210 and favia bad at 250, good at 170 great at 110. All these were various Ora corals.

Far from the OP question but that seems to have been answered, thought it could be useful info.
 
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