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Old 08/03/2013, 11:10 AM   #1
Ron Reefman
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led spectrum shift due to dimming?

OK, a simple question that I have never seen the answer to, and I tried doing some searching. But I didn't find anything really on point.

How much does the spectral output of an led change as it is dimmed from 100% power to turning off?

My assumption is that because leds work in a narrow power band (I think) and because they output light in a narrow range of wavelength, that any spectrum shift would be quite small. But somebody has pressed me on this point, claiming that running leds at dimmed levels can change the spectrum of the leds and cause 'problems'. He over stated the 'problems' in his argument to me, but we don't need to go there (unless you agree).

I found research on the intensity of the led as power is reduced by dimming, but that's not the issue. We all know there is less light, and some dimmers are better and more linear than others. But as you turn down the power, the light gets dimmer, but does it change from 420nm at 100% power to some other spectrum, say 415nm, or 410nm, or maybe the other way, to 425nm, or 430nm?

I don't have any problem with this being a wide open discussion, but I would like to try and find some real science and not just, "When I dim my lights they get more blue." That doesn't help much. Know what I mean?


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Old 08/03/2013, 12:11 PM   #2
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Interesting question, Ron.

I found this sheet with a Google search:
http://www.lrc.rpi.edu/programs/soli...PIE6337-17.pdf

There does appear to be a +/- 10 to 15 nm shift depending on the type of dimming. I did not see where they specified the brand of diodes used but the they are indium gallium nitride (InGaN) based, and so are CREE LED's.


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Old 08/03/2013, 12:44 PM   #3
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Van, OK so I suck at the google search. That's why I'm married to a head librarian. But she was busy cutting the grass and doing yard work in the 90 degree plus heat... hey, it's her choice, not mine.

Anyway, thanks a ton for the link. That is exactly the kind of data I wanted to find. You rock man!


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Old 08/03/2013, 03:37 PM   #4
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Now the next question is Ron, is this good or bad? Assuming that the average reefer ramped the LED's up and down over the course of a few hours, and maintained the known color combination desired for a few hours (ie 6 hours), then could this possibly be very beneficial to corals vs detrimental? Most LED builders are understanding the need for a more complete light spectrum with their fixtures. Assuming that you were ramping up and down over several hours, you might be able to achieve a much broader spectrum then originally planned, thus benefiting the corals (or the algae conversely). Of course all lights will color shift over time.


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Old 08/03/2013, 03:47 PM   #5
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^^^ so the corals through out they day would experience +- 15 nm which really does put a whole new meaning to full spectrum. Now all the suddon a 420nm violet can give out 405-435 nm throughout a days time


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Old 08/04/2013, 05:24 AM   #6
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Quote:
Originally Posted by hypnoj View Post
Now the next question is Ron, is this good or bad? Assuming that the average reefer ramped the LED's up and down over the course of a few hours, and maintained the known color combination desired for a few hours (ie 6 hours), then could this possibly be very beneficial to corals vs detrimental? Most LED builders are understanding the need for a more complete light spectrum with their fixtures. Assuming that you were ramping up and down over several hours, you might be able to achieve a much broader spectrum then originally planned, thus benefiting the corals (or the algae conversely). Of course all lights will color shift over time.
Is that good or bad? hmmm... I don't know. My first thought is it's probably OK. If you have a fixture with the led colors you want and everybody, you, the corals, the fish, etc., are happy with it, I don't think that a 10nm shift either way is going to be much of an issue. What do you think? I change the total color spectrum of my lights almost every hour except for 5 hours of midday and overnight. But that's not really the same as changing the spectrum of specific leds. But the data we have shows only about a 10nm shift from 100% to 0%. And at the lower power setting, say anything under 50%, the PAR is down so much the effect on the corals would be reduced as well, right? I don't see it as much of an issue, but then I'm one of those people that believe too many reefers (especially reefers using leds) obsess over getting the colors just right. I think if you have enough PAR in the 400nm to 500nm range and some small amount of most of the rest of the spectrum, your corals will adapt, colors will be OK and you can see them in a light that pleases your eye. A friend and I bought new fixtures for our tanks. What we bought had basically 200 leds for 180g sps & lps dominate reefs. His leaned more to the 400nm to 450nm as far as blues and more cool white as far as whites went. I did a much more varied mix with all kinds of blue and a fairly even mix of all 3 whites. Seven months later, we both still have great looking tanks. I see people fretting about whether they should use 450nm or 460nm... I never thought it made much difference, and now that we see they may change that much anyway, I feel even stronger about the idea that it's not that big a deal. As for whether ALL lights color shift over time? That's a whole different topic. I know leds do get weaker over time. Some commonly quoted numbers are like 2% or 3% a year. But do they color shift? My guess is probably yes, but the more important data is how much and over how long?


Quote:
Originally Posted by YoungREEFA View Post
^^^ so the corals through out they day would experience +- 15 nm which really does put a whole new meaning to full spectrum. Now all the sudden a 420nm violet can give out 405-435nm throughout a days time
I think, based on the data we've seen so far, you might be over stating the case a bit. I see mostly 10nm shifts, not 15nm (and that is splitting hairs anyway). And yes, it can be +/- but they seemed to only go one way (depending on how you control the power). Some go + and some go -, but saying you get a 30nm spread from any particular led in your fixture is a bit over stated. Your fixture only uses one method of dimming, so the fact that a particular led has a +/- spread of 30nm based on 2 different methods of dimming, isn't really accurate for your specific fixture. Finally, this shift takes place over power settings from 100% to 0%. And looking at the graphs, in 3 out of 4 cases, the vast majority of the shift happens between 50% and 0% power. And in my tank, 50% to 0% power is producing much less PAR so any bad effects on a coral would be reduced.

So this study gives us something to discuss, but I'd really like to see at least 1 more study, maybe 2 (assuming we can find any), just to confirm these findings. I'm going to do more searching, and if anybody else has any data, I'd like to hear it. And opinions about whether this shifting is good, bad or neutral are welcome too. And hypnoj brought up a secondary question we could look into, do leds color shift over time? Ah well, we'll see if anybody can find any studies for that question too.


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Old 08/04/2013, 07:43 AM   #7
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Hi Ron,
I hope that it should help - below you can find several charts for different LED(UV - made for us, the rest - Cree) for different power setting(PWM dimming).
There was done two measurements - on 5% and 100% power.
As you can see - for some kind of leds spectrum shift is very small(few nm after dim to 5% from 100%) - so I cant confirm that there is possible +/- 10% or even +/- 15% spectrum shift for MONOCHROMATIC leds.
It looks completely different for cool white and neutral whie leds(little cooler than warm white - they have high CRI and was used in our R2 series led lamps - like Tritons R2 or Hyperions R2).
As you can see, in cool white - when LED is dimmed to 5% - overal spectrum is cooler than on 100%. The difference is huge. The same with Neutral White leds - they are warmer on 5% than on 100%.
I hope that charts will be useful for you.

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Old 08/04/2013, 11:38 AM   #8
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Przemek, thanks for the graphs! Now I just want to be sure I understand what I'm looking at!

The top 3 graphs show almost identical peaks. That means little shift of spectrum, right? And as we work down the slopes to lower intensities the graphs start to separate, showing more or less range of spectrum at those lower intensities. Am I getting this right?

The next 2 show a bit of a separation even at the peak of the graph, so a bit more shift in spectrum compared to the first 3 graphs. Right?

And the last 2, the whites, the 400nm to 450nm or 475nm looks pretty similar at 5% or 100%, but the longer wavelengths separate much more. But they still cover the same basic spectrum, just at much different intensities. So the same over all spectrum is covered, but the total color of the white light would change (a shift in Kelvin rather than spectrum). Am I even close on that one?

Thanks


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Old 08/04/2013, 04:00 PM   #9
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The drift the study above refers to would be a shift in the peak wavelength of light the LED emits. This would be respresented by a shift of the peak from left to right. With white LEDs the shift we are seeing is in intensity of various wavelengths which is shown by a vertical shift and according to these graphs the longer wavelengths do lose more intensity than the shorter.

I am curious as to why the monochromatic LEDs have the same intensity whether run at 5% or 100%.


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Old 08/12/2013, 08:58 AM   #10
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Im sorry, I missed your post jerpa.
They dont have the same intensity.
During measurments we are setting different Imtegration time(time needed for "catching" lightwaves and coutn them).
For 100% we set 3ms time, for 5% - 100ms.
I hope thats clear now.



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Old 08/12/2013, 09:04 AM   #11
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@Ron
Exactly, first three charts have minimal spectrum shift.
Last two show that warm led on low intensiy are much "warmer" and cool white are much cooler than on 100% power.


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Old 08/12/2013, 03:08 PM   #12
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Thanks Przemek. I was hoping I got that right.

I asked this in a different thread and got refered back to a post by you that is a bit over my head... well, I didn't understand it clearly. I see people talk about reflected light and that make perfect sense to me. But emitted light? Define emitted. Are you saying the coral (pigment) is making a color rather than reflecting it? The only thing that comes to mind for me is bioluminescence, that's different, right? So explain emitted light in simple terms for me. Thanks!


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Old 08/12/2013, 03:34 PM   #13
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Ron, I can try to do it but my technical english is very poor...
There is few "key" words which we need to udnerstand.
I will try to do it with some "smart" explanation from Wiki pedia.
As you remember, in that other thread we was talking about corals pigments - there are few different types - GFP(Green Fluorescent Proteins), DsRed(DS type pigments responsible for "red" color in corals, RedFlo - red fluorescent proteins etc).
As you read in t he other thread, I explained why some corals are extremaly green in blue leds. Its depend from their pigment(GFP) and "stoke shift"..
What it is?
Stokes shift

From Wikipedia, the free encyclopedia
Stokes shift is the difference (in wavelength or frequency units) between positions of the band maxima of the absorption and emission spectra (fluorescence and Raman being two examples) of the same electronic transition.[1] It is named after Irish physicist George G. Stokes.[2] [3] [4]

When a system (be it a molecule or atom) absorbs a photon, it gains energy and enters an excited state. One way for the system to relax is to emit a photon, thus losing its energy (another method would be the loss of heat energy). When the emitted photon has less energy than the absorbed photon, this energy difference is the Stokes shift. If the emitted photon has more energy, the energy difference is called an anti-Stokes shift;[5] this extra energy comes from dissipation of thermal phonons in a crystal lattice, cooling the crystal in the process. Yttrium oxysulfide doped with gadolinium oxysulfide is a common industrial anti-Stokes pigment, absorbing in the near-infrared and emitting in the visible portion of the spectrum. Photon upconversion is another anti-Stokes process.

Stokes fluorescence[edit]

Stokes fluorescence is the re-emission of longer wavelength photons (lower frequency or energy) by a molecule that has absorbed photons of shorter wavelengths (higher frequency or energy).[6] Both absorption and radiation (emission) of energy are unique characteristics of a particular molecular structure. If a material has a direct bandgap in the range of visible light, the light shining on it is absorbed, causing electrons to become excited to a higher energy state. The electrons remain in the excited state for about 10−8 seconds. This number varies over several orders of magnitude depending on the sample, and is known as the fluorescence lifetime of the sample. After losing a small amount of energy in some way (hence the longer wavelength), the electron returns to the ground state and energy is emitted.



So - if we will use blue light (coming from led for example) and we will have coral which have GFP in his tissue with "stoke shift" 80nm - its mean, that it will "absorb" blue light, take some energy - and emit green fluorescent light..
If that coral will have RedFlo proteins - like Pocillopora damicornis(pigment P625 - from chart below) - it will "absorb" lighwaves from 570-575nm area - and will "emit"(extication range) lightwaves with langht 625nm - orange.(please see chart)


If we are talking about reflection - its much easier to explain.
For example - we have light source build from violer, blue and green leds.
Some pigment only "reflect" lightwaves without "changing" their lenght(color - without "taking their energy"). So - if any coral will have "reflect" pigment (for example orange) and it will not be lighted by light with orange lightwaves in output - it never will be orange for our eyes - becuase there will not be any light(from "orange" area) which can be reflected..
I hope that it was clear -and you was able to understand my "inglish" .


Regards

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Old 08/13/2013, 12:32 AM   #14
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Interesting. However, the initial study linked only had shifts of +- 10nm at max, I think. The royal blues only shifted a little bit; 5nm at max. In contrast, the reds were closer to the 10nm mark.


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Old 08/13/2013, 01:48 AM   #15
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It can depend from manufacturer - good Cree leds have shifts like in above charts..


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Old 08/13/2013, 02:36 AM   #16
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My understanding was that 0-10v dimming would shift but not pwm but it seems based on whats being said here that isnt true?


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Old 08/13/2013, 04:15 AM   #17
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1-10V dimming for leds?? How you want to do it??
Any "1-10V" module change analog signal(1-10V) to digital(PWM).


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Old 08/13/2013, 05:52 AM   #18
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Przemek,
I think I understand it better now. So I'll try an explination and you tell me if I've got it, and ask another question.

A pigment that reflects light does just that, reflect back a given wavelength it receives from the light source. So an object that is red under a white light source will be colorless (black or gray) under a 450nm only light source because there is no red wavelength light to reflect.


A pigment that emits light absorbs some of the energy from a specific wavelength and then emits light back as a longer wavelength (less energy). So pigment P620 absorbs light of 440nm (blue/violet) and emits light at 620nm so it looks orange even though it is only under a blue/violet 440nm light.

So what does this pigment look like under a full spectrum white light? Is it still just 620nm as an emitted light, or does it also reflect a color back as well. I guess what I'm asking is, are reflected and emitted light mutually exclusive, i.e. the pigment P620 looks 620nm orange in both white light and 440nm blue light. Or does pigment P620 emit light at 620nm while reflecting a different color under a full spectrum white light? And under a light that was only 550nm, pigment P620 would also be colorless (some shade of black or gray)?

This is fun to learn Przemek, and I really appreciate your taking the time to teach it to me ... but my head is starting to hurt!


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Old 08/13/2013, 06:21 AM   #19
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A pigment that reflects light does just that, reflect back a given wavelength it receives from the light source. So an object that is red under a white light source will be colorless (black or gray) under a 450nm only light source because there is no red wavelength light to reflect.
Yes, exactly - you will not able to see "red" color og that object - because it cant reflect lightwaves coming from that range..

A pigment that emits light absorbs some of the energy from a specific wavelength and then emits light back as a longer wavelength (less energy). So pigment P620 absorbs light of 440nm (blue/violet) and emits light at 620nm so it looks orange even though it is only under a blue/violet 440nm light.
Yes.

So what does this pigment look like under a full spectrum white light? Is it still just 620nm as an emitted light, or does it also reflect a color back as well. I guess what I'm asking is, are reflected and emitted light mutually exclusive, i.e. the pigment P620 looks 620nm orange in both white light and 440nm blue light. Or does pigment P620 emit light at 620nm while reflecting a different color under a full spectrum white light? And under a light that was only 550nm, pigment P620 would also be colorless (some shade of black or gray)?
It will work the same - pigment will absorb light coming from 440nm blue light and will emit it in 620nm area. Additionally, that pigment will reflect some lightwaves coming from ca.620nm area, because that "blue light 440nm" make them "similar" to not fluorescent pigments - like DsRed.
I will give you example..
Do you have any SPS corals imported from Bali? They are looking AMAZING in first days after transport.. They have very stron colors(visible) because some of lightwaves are "reflected" from their pigments..
But..
After some days/weeks, because that pigments wasnt properly "lighted"(like pigments from 500nm) they are start shadowing and decrease..
Coral loose his colour - and it no matter that in first days it was colorfull.
It was colorfull, because in his natural environment his tissue was "bombarded" by photons coming from area which make his - for example - pink pigment visible to our eyes(green spectrum and violet).. But - after "turning off" that kind of light - that pigment will slowly disappear...
Now its clear?


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Old 08/13/2013, 10:47 AM   #20
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That is very interesting and very well explained. Thank you very much.


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Old 08/13/2013, 11:13 AM   #21
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Great :-)


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Old 08/13/2013, 12:59 PM   #22
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Pardon my intrusion on the thread, but...

Przemek,

Thanks for the chart. I didn'trealize the impact some frequencies had on color.

In your chart, it appears that the 560 to 590 nm range contributes a lot to the color of many Acro's, particularly the blue ones. Most of us using LEDs don't have a lot of coverage in those spectrums. Could that be the reason that coral coral coloration under LED might be different?

By the way... Great question Ron!


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Old 08/13/2013, 01:25 PM   #23
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Quote:
Originally Posted by Pacific Sun RD View Post
Im sorry, I missed your post jerpa.
They dont have the same intensity.
During measurments we are setting different Imtegration time(time needed for "catching" lightwaves and coutn them).
For 100% we set 3ms time, for 5% - 100ms.
I hope thats clear now.
Thanks for the clarification.


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Old 08/13/2013, 01:55 PM   #24
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Quote:
Originally Posted by reefgeezer View Post
Pardon my intrusion on the thread, but...

Przemek,

Thanks for the chart. I didn'trealize the impact some frequencies had on color.

In your chart, it appears that the 560 to 590 nm range contributes a lot to the color of many Acro's, particularly the blue ones. Most of us using LEDs don't have a lot of coverage in those spectrums. Could that be the reason that coral coral coloration under LED might be different?

By the way... Great question Ron!
Good question too
Many of Acroporas have two or more pigments in their tissue - and when all they "play" in proper light - we can see real colors of coral.
Im sure that you saw many time the same coral(lile very popular A. valida) which look different under MH, T5 and leds(from purple to blue)
Reason - not all pigments are properly "triggered" - some colors can change...
Its like "mixing" paint - when you will add more "red" to blue - it will be pink/violet.
A. valida have three different pigments - and when I saw "original" colors when I dive in Bali I was very suprise how it looks in "real"..
Thats a reason why under mh light source("full spectrum") that coral have different color than under T5(even newest tri-phoshor tubes) and leds..


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