Do LEDs color shift when dimmed?

[Bilk]

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.

That is useful info. I'm running two 100w 12k Cannons. I've been afraid to run them at an intensity higher than 50% at 16" above the water. I'm either going to have to raise them further or replace them. They may be for a much deeper tank than mine or over a larger tank and mounted much higher for the spread. I ordered an Apogee meter this afternoon.

 

[jedimasterben]

http://s.reefcentral.com/forums/showpost.php?p=21774928&postcount=7

I have a few questions - how was dimming achieved, through voltage control, analog, or PWM? What were the temperatures of each LED at each setting? Were voltages within spec? Spectral shift (of the extent that you saw on some of the chips) should only occur if something is out of spec or when there are drastic changes in temperature, such as a chip going from 0C to 60C, etc.

 

[Aqualund]

As for the measured values before negative effects are concerned...it should be considered that most of the bad effects from leds on sps has been from running the whites too high. Typically you can run above 250 par as long as your whites are comprising only about 20% of your total light. Of course, these numbers arent specific, but it's what I have mine running at on my arduino....and I have about 350 par in my bright spots for my milleporas and acroporas. Going on 2 years with no bleaching or loss of color, in fact I'm thinking of upping the intensity next week.

 

[Aqualund]

I have a few questions - how was dimming achieved, through voltage control, analog, or PWM? What were the temperatures of each LED at each setting? Were voltages within spec? Spectral shift (of the extent that you saw on some of the chips) should only occur if something is out of spec or when there are drastic changes in temperature, such as a chip going from 0C to 60C, etc.

It also occurred in this paper:

http://www.lighting.rpi.edu/programs/solidstate/pdf/dyble-spie2005.pdf

 

[jedimasterben]

As for the measured values before negative effects are concerned...it should be considered that most of the bad effects from leds on sps has been from running the whites too high. Typically you can run above 250 par as long as your whites are comprising only about 20% of your total light. Of course, these numbers arent specific, but it's what I have mine running at on my arduino....and I have about 350 par in my bright spots for my milleporas and acroporas. Going on 2 years with no bleaching or loss of color, in fact I'm thinking of upping the intensity next week.

Please stop spreading that garbage around. It wasn't true when it was made up a few years ago by people that don't understand LEDs and it is still not true today. If white LEDs kill corals, why is it that people can use warm white halides to light their tanks, such as the Iwasaki 6500K, and have immense coral growth? Those bulbs emit significantly more 500nm+ than they do sub-500nm.

Iwasaki 6500K

The most common array for growing corals, 1:1 cool white to royal blue

 

[Aqualund]

I understand LED's just fine. It's quite simple that for a majority of sps corals, you will get the best coloration and polyp extension with blue(er) light. Epicreefer said at 225 par his corals looked bleached, I merely stated that if you tone down the whites that wont happen. I did not say white leds kill coral.

Because of course as you know 225 par is not the upper limit on sps coloration and health.

Im not sure I know anyone or have seen anyone that runs only white leds or halides at 250+ par above their sps tanks and expects good coloration and growth.

Most everyone that runs leds these days has found the best combination of light by doing 80% blue and 20% white in their combinations.

anyone that has done a 1:1 rb/cw leds at equal intensities has run into long term problems. It's fine for LPS, but not sps.

why is it that people can use warm white halides to light their tanks, such as the Iwasaki 6500K, and have immense coral growth?

I would further contend which corals? are we talking sps? if so, which species? There are pretty broad lighting needs, where some corals do better with warmer light, whereas others cannot stand warmer light. Also, show me a tank that is running just the Iwasaki 6500k, and it is doing better in color, growth and polyp extension over a 2 year period with a variety of SPS corals than say a radium 20k.

 

[jedimasterben]

I understand LED's just fine. It's quite simple that for a majority of sps corals, you will get the best coloration and polyp extension with blue(er) light. Epicreefer said at 225 par his corals looked bleached, I merely stated that if you tone down the whites that wont happen. I did not say white leds kill coral.

Because of course as you know 225 par is not the upper limit on sps coloration and health.

Im not sure I know anyone or have seen anyone that runs only white leds or halides at 250+ par above their sps tanks and expects good coloration and growth.

Most everyone that runs leds these days has found the best combination of light by doing 80% blue and 20% white in their combinations.

anyone that has done a 1:1 rb/cw leds at equal intensities has run into long term problems. It's fine for LPS, but not sps.

I would further contend which corals? are we talking sps? if so, which species? There are pretty broad lighting needs, where some corals do better with warmer light, whereas others cannot stand warmer light. Also, show me a tank that is running just the Iwasaki 6500k, and it is doing better in color, growth and polyp extension over a 2 year period with a variety of SPS corals than say a radium 20k.

...it should be considered that most of the bad effects from leds on sps has been from running the whites too high...

Care to extrapolate on these 'bad effects'?

225 PAR is very close to the upper limit of nearly all corals' photosynthetic process. 350 PAR gets the rest, minus some outliers. Some will tolerate more light through the use of pigments to fluoresce the light away, or rely on the xanthophyll cycle.

Again, what are these long-term problems? Corals don't care much about the light above them as long as there is enough of it or not too much of it, and has enough of it be in the 400-700nm range.

Going back to the days before high-kelvin bulbs existed, that's all that were used with great success on all corals that were kept during that time, SPS, LPS, soft and octocorals, etc, and they paved the way for where the hobby is now. If you do some searching around, there are still plenty on this forum and other that consider the 6500K Iwasaki to be the best light for coral growth.

 

[Bilk]

Care to extrapolate on these 'bad effects'?

225 PAR is very close to the upper limit of nearly all corals' photosynthetic process. 350 PAR gets the rest, minus some outliers. Some will tolerate more light through the use of pigments to fluoresce the light away, or rely on the xanthophyll cycle.

Again, what are these long-term problems? Corals don't care much about the light above them as long as there is enough of it or not too much of it, and has enough of it be in the 400-700nm range.

Going back to the days before high-kelvin bulbs existed, that's all that were used with great success on all corals that were kept during that time, SPS, LPS, soft and octocorals, etc, and they paved the way for where the hobby is now. If you do some searching around, there are still plenty on this forum and other that consider the 6500K Iwasaki to be the best light for coral growth.

I'm still trying to better understand the lighting issues with LEDs in relation to the requirements of the corals we keep, so no expert here by any stretch. However I was in the hobby in the 80s and 90s when lighting was the limitation for SPS thriving in systems. Back then I ran VHO and eventually halide. The bulbs then were not tweaked for great success with SPS. I believed that has changed quite a bit in both fluorescent and MH.

I think where Aqua is heading with his opinion is not only good growth, but good coloration. Do you feel that 6500k give the best coloration for corals? Or does that need to be supplemented with higher kelvin bulbs? We know par isn't the only variable to be concerned with.

 

[jedimasterben]

I'm still trying to better understand the lighting issues with LEDs in relation to the requirements of the corals we keep, so no expert here by any stretch. However I was in the hobby in the 80s and 90s when lighting was the limitation for SPS thriving in systems. Back then I ran VHO and eventually halide. The bulbs then were not tweaked for great success with SPS. I believed that has changed quite a bit in both fluorescent and MH.

I think where Aqua is heading with his opinion is not only good growth, but good coloration. Do you feel that 6500k give the best coloration for corals? Or does that need to be supplemented with higher kelvin bulbs? We know par isn't the only variable to be concerned with.

Bulbs are very different now than what were available then. It took a long time for a manufacturer to step up and apply custom phosphors. Still hasn't really happened with LEDs, but they are pretty much where they need to be, anyway, their limitations are different than the limitation with halides and fluorescents as far as wavelength shifting goes.

6500K (and other 'white' lighting) gives natural coloration. If you've ever been diving, you've seen that the reef crest is comprised of a couple of colorful tabling acropora or pocillopora surrounded by a sea of golden browns, with sections like that covering every bit of the reef. If that's the kind of coloration you are after, then that is lighting you'd want to use. If you're only looking for fluorescence, then eliminate as much green and red as possible. If you want great non-fluorescent coloration in addition to fluorescent 'pop', you need to find a happy median, but the more green and red you add, the more that fluorescence will be 'drowned out'.

 

[Bilk]

Bulbs are very different now than what were available then. It took a long time for a manufacturer to step up and apply custom phosphors. Still hasn't really happened with LEDs, but they are pretty much where they need to be, anyway, their limitations are different than the limitation with halides and fluorescents as far as wavelength shifting goes.

6500K (and other 'white' lighting) gives natural coloration. If you've ever been diving, you've seen that the reef crest is comprised of a couple of colorful tabling acropora or pocillopora surrounded by a sea of golden browns, with sections like that covering every bit of the reef. If that's the kind of coloration you are after, then that is lighting you'd want to use. If you're only looking for fluorescence, then eliminate as much green and red as possible. If you want great non-fluorescent coloration in addition to fluorescent 'pop', you need to find a happy median, but the more green and red you add, the more that fluorescence will be 'drowned out'.

Agree with everything you stated here based on my earlier experiences in the hobby and what little I understand about LED. I also agree that many corals in the wild are much different in appearance than what we look to achieve in out tanks. Someone called me out on that here before I've been diving and have seen reefs up close and personal

 

[Aqualund]

Care to extrapolate on these 'bad effects'?

225 PAR is very close to the upper limit of nearly all corals' photosynthetic process. 350 PAR gets the rest, minus some outliers. Some will tolerate more light through the use of pigments to fluoresce the light away, or rely on the xanthophyll cycle.

Par maybe, but PUR is more applicable, and therefore With the right mix of color (more 20k than 6.5k) then you could have a higher PAR, but still be beneficial because it is a more appropriate PUR for the organism.

But yes, I would agree that about 250 PAR with a 1:1 cw/rb ratio is pretty much the upper limit for most sps. This corresponds greatly with everything I have said thus far.

The history of good growth with the 6500K is most notably with LPS, and softies (zoos and palys included), and a sprinkle of shallow reef sps here and there. Most definitely some of the more delicate deepwater sps corals will not benefit more from a 6500K bulb.

This can be most of the reason a lot of people experience "negative results" with their sps when they hook up their 1:1 leds over their tank at 250 par. Negative effects being pale color, bleaching, polyp retraction, and stn/rtn within days. First an examination of the types of sps housed should be considered and determine if those sps would be better suited towards a 20k look than a 6500k footprint.

The reality is, most of these corals never see the amount of yellow and red that these white lights are putting out, but we like the coloration it gives the normally "brown in the wild" coral. It is a balance between what can potentially hurt the coral if not acclimated properly, to what looks best.

 

[jedimasterben]

Agree with everything you stated here based on my earlier experiences in the hobby and what little I understand about LED. I also agree that many corals in the wild are much different in appearance than what we look to achieve in out tanks. Someone called me out on that here before I've been diving and have seen reefs up close and personal

Not quite like the neon tanks that a lot seem to keep these days, but the natural reefs have beauty beyond compare

Par maybe, but PUR is more applicable, and therefore With the right mix of color (more 20k than 6.5k) then you could have a higher PAR, but still be beneficial because it is a more appropriate PUR for the organism.

But yes, I would agree that about 250 PAR with a 1:1 cw/rb ratio is pretty much the upper limit for most sps. This corresponds greatly with everything I have said thus far.

The history of good growth with the 6500K is most notably with LPS, and softies (zoos and palys included), and a sprinkle of shallow reef sps here and there. Most definitely some of the more delicate deepwater sps corals will not benefit more from a 6500K bulb.

This can be most of the reason a lot of people experience "negative results" with their sps when they hook up their 1:1 leds over their tank at 250 par. Negative effects being pale color, bleaching, polyp retraction, and stn/rtn within days. First an examination of the types of sps housed should be considered and determine if those sps would be better suited towards a 20k look than a 6500k footprint.

The reality is, most of these corals never see the amount of yellow and red that these white lights are putting out, but we like the coloration it gives the normally "brown in the wild" coral. It is a balance between what can potentially hurt the coral if not acclimated properly, to what looks best.

Keep in mind that corals can absorb light across the full light spectrum with various efficiency, with blue light having the most absorption. Also keep in mind that photosynthetic pigments themselves do not change across different types of corals, only which ones are present and in what amounts that are within the zooxanthellae. PCP (complex of four peridinin and one chlorophyll a molecules) alone extends the 'efficient' absorption of chlorophyll a well beyond the 430nm spike/dropoff.

Absorption at 530nm is as good as 450nm, and that is only two pigments - corals typically contain several more, but at the very least all have chlorophyll a and peridinin, I've never seen data that says otherwise. Looking over the data that is available (and most of it from the 60s) throws what most people think of PUR out the window.

250 PAR is nearing the limit no matter what light source. You can get away with more PAR from 'white' light sources due to decreased absorption efficiency in higher green and red, but not much more, and it is a waste of energy to have too much.

FYI, a lot of the 'deepwater' SPS out there are collected on or near the reef crest. The term is a misnomer. There are deeper-collected Acropora (down to around 15m or so), but they aren't as common as the name 'deepwater'.

20K is also a made-up number. Anything over 8,000K is extremely difficult to measure, and since there is no standard, you can call any light any Kelvin temp and you would be 100% correct.

The main issue with people overlighting their tanks has nothing to do with white LEDs - it has basically everything to do with packing the light with LEDs, throwing tight optics on them, and then cranking them up until they look as bright as the previous lighting. With tight lenses, you can go from 100 PAR to 600 within a few inches of horizontal space at the same height. Corals do far better with distributed, even lighting than they do with such extreme point-source light.

Most corals also never see anywhere near the amount of total light they receive in the wild nor the spectral width, yet they don't suffer from that, nor the lack of particulate food and prey, etc.

 

[Pacific Sun RD]

I have a few questions - how was dimming achieved, through voltage control, analog, or PWM? What were the temperatures of each LED at each setting? Were voltages within spec? Spectral shift (of the extent that you saw on some of the chips) should only occur if something is out of spec or when there are drastic changes in temperature, such as a chip going from 0C to 60C, etc.

LED can be dimmed ONLY by current change(decrease).
Its not possible to dim them by voltage control, analog(? what you mean?).
PWM is the best and mostly used method to control led power.
in that charts there was used lamp with SMT matrix and regular R2(Hyperion R2) - all tests made after panel reach target temperature for set power.

 

[Pacific Sun RD]

Bulbs are very different now than what were available then. It took a long time for a manufacturer to step up and apply custom phosphors. Still hasn't really happened with LEDs, but they are pretty much where they need to be, anyway, their limitations are different than the limitation with halides and fluorescents as far as wavelength shifting goes.

6500K (and other 'white' lighting) gives natural coloration. If you've ever been diving, you've seen that the reef crest is comprised of a couple of colorful tabling acropora or pocillopora surrounded by a sea of golden browns, with sections like that covering every bit of the reef. If that's the kind of coloration you are after, then that is lighting you'd want to use. If you're only looking for fluorescence, then eliminate as much green and red as possible. If you want great non-fluorescent coloration in addition to fluorescent 'pop', you need to find a happy median, but the more green and red you add, the more that fluorescence will be 'drowned out'.

You are not able to reach good colored sps corals with all nice looking pigments under 6500k metal halide bulb(even if it will be iwaki).
It will not give you natural coloration - it will brown your corals with very good growth rate.
Of course, some corals with DsRed pigments like Pocci/Styllo/Birdnest will look very good - but ONLY because they dont have(mostly) GFP proteins.
They used another type of proteins responsible for their nice(wamr) looking - and excitation range is covered by warm "light" lightsources.

 

[Pacific Sun RD]

Not quite like the neon tanks that a lot seem to keep these days, but the natural reefs have beauty beyond compare


Keep in mind that corals can absorb light across the full light spectrum with various efficiency, with blue light having the most absorption. Also keep in mind that photosynthetic pigments themselves do not change across different types of corals, only which ones are present and in what amounts that are within the zooxanthellae. PCP (complex of four peridinin and one chlorophyll a molecules) alone extends the 'efficient' absorption of chlorophyll a well beyond the 430nm spike/dropoff.

Absorption at 530nm is as good as 450nm, and that is only two pigments - corals typically contain several more, but at the very least all have chlorophyll a and peridinin, I've never seen data that says otherwise. Looking over the data that is available (and most of it from the 60s) throws what most people think of PUR out the window.

250 PAR is nearing the limit no matter what light source. You can get away with more PAR from 'white' light sources due to decreased absorption efficiency in higher green and red, but not much more, and it is a waste of energy to have too much.

FYI, a lot of the 'deepwater' SPS out there are collected on or near the reef crest. The term is a misnomer. There are deeper-collected Acropora (down to around 15m or so), but they aren't as common as the name 'deepwater'.

20K is also a made-up number. Anything over 8,000K is extremely difficult to measure, and since there is no standard, you can call any light any Kelvin temp and you would be 100% correct.

The main issue with people overlighting their tanks has nothing to do with white LEDs - it has basically everything to do with packing the light with LEDs, throwing tight optics on them, and then cranking them up until they look as bright as the previous lighting. With tight lenses, you can go from 100 PAR to 600 within a few inches of horizontal space at the same height. Corals do far better with distributed, even lighting than they do with such extreme point-source light.

Most corals also never see anywhere near the amount of total light they receive in the wild nor the spectral width, yet they don't suffer from that, nor the lack of particulate food and prey, etc.

You mistake Chl_a and pigments.
That "thing" what gives coral "food" is not the same "thing' which give them nice looking colors.
About pigmetns - check below chart for excitation/emision chart for GFP pigments - you will see that there is no any above 600nm - its mean " red" light.Almost 65% of them is below 470 and 510nm.

 

[jda]

I'm still trying to better understand the lighting issues with LEDs in relation to the requirements of the corals we keep, so no expert here by any stretch. However I was in the hobby in the 80s and 90s when lighting was the limitation for SPS thriving in systems. Back then I ran VHO and eventually halide. The bulbs then were not tweaked for great success with SPS. I believed that has changed quite a bit in both fluorescent and MH.

I think where Aqua is heading with his opinion is not only good growth, but good coloration. Do you feel that 6500k give the best coloration for corals? Or does that need to be supplemented with higher kelvin bulbs? We know par isn't the only variable to be concerned with.

The light serves 2 purposes. First, some is absorbed by the coral, used and spit back out at a higher frequency with less energy. Second, some gets reflected. Both of these combine for what our eyes perceive as color.

You absolutely need to supply the right kind of light for the coral to use it for energy. Period. Lots of lights can handle this. Provided that you do this, then the rest of the light will reflect it as you shine - 10K will reflect differently than 20K... this is personal preference. None of these will look like they did in the ocean where there is typically less blue light - I doubt that many of us would want the colors in the ocean that I have seen.

If you are interested I can provide a handful of reasons why LED don't give quite as good of color to SPS than other light (as judged by long-time hobbyists with a wide breath and depth of experience with different lights and corals), but I don't want to further lead to an argument.

 

[Bilk]

The light serves 2 purposes. First, some is absorbed by the coral, used and spit back out at a higher frequency with less energy. Second, some gets reflected. Both of these combine for what our eyes perceive as color.

You absolutely need to supply the right kind of light for the coral to use it for energy. Period. Lots of lights can handle this. Provided that you do this, then the rest of the light will reflect it as you shine - 10K will reflect differently than 20K... this is personal preference. None of these will look like they did in the ocean where there is typically less blue light - I doubt that many of us would want the colors in the ocean that I have seen.

If you are interested I can provide a handful of reasons why LED don't give quite as good of color to SPS than other light (as judged by long-time hobbyists with a wide breath and depth of experience with different lights and corals), but I don't want to further lead to an argument.

I am pretty sure I have a good understanding of what's happening in our tanks in terms of how light is utilized by corals and the irradiance corals exhibit under different light sources and spectra. What I was more interested here was in how dimming might effect the spectral qualities of the light, i.e. does the light significantly change chromatically when dimmed.

As for utilizing another lighting source, MH is out of the question afaik in my situation. I don't want to deal with the heat gain in the room where the tank is located, so LED and possible supplementation using T5 are the only options. I've seen plenty of worthy tanks with LED to be convinced they are a very viable source for growing healthy corals.

 

[Bilk]

I'm happy I started this thread. A lot of good information is "coming to light"

 

[Epicreefer]

Origionaly all the cannons were run at 100%. I added a diy dimmer to about half of them, the rock scape in not level, half is a ridge 5' from the lights and half is a pillar that puts the corals on top at 2' from the lights. These on top of the pillar are the majority that were doing bad, but the lps were all bellow the top ridge, about 7', partially shaded ones did best. Were going to put the new controllers/dimmers on all the lights eventually, probably a few months. The problem with running the white lights at 20% is the tank looks way too blue so dimming the lights on one side semi evenly and re aiming others was the solution we came up with.

 

[jedimasterben]

LED can be dimmed ONLY by current change(decrease).
Its not possible to dim them by voltage control, analog(? what you mean?).
PWM is the best and mostly used method to control led power.
in that charts there was used lamp with SMT matrix and regular R2(Hyperion R2) - all tests made after panel reach target temperature for set power.

LEDs can be controlled via voltage, as well as via current. Current dimming allows for full control of output, voltage is much more limited (since LEDs have a minimum strike voltage) but does allow for much cheaper control so there are some fixtures out there that use it (they are older, though, pretty much any newer fixture will have 0-100% dimming on regular constant current drivers).

You are not able to reach good colored sps corals with all nice looking pigments under 6500k metal halide bulb(even if it will be iwaki).
It will not give you natural coloration - it will brown your corals with very good growth rate.
Of course, some corals with DsRed pigments like Pocci/Styllo/Birdnest will look very good - but ONLY because they dont have(mostly) GFP proteins.
They used another type of proteins responsible for their nice(wamr) looking - and excitation range is covered by warm "light" lightsources.

The color achieved using lower-kelvin bulbs is the natural color. Coral reefs are dominated by shades of brown, especially in SPS corals. Keeping them in our tanks causes drastic color shifts in most of them, which while unnatural, is usually for the better :thumbsup:

You mistake Chl_a and pigments.
That "thing" what gives coral "food" is not the same "thing' which give them nice looking colors.
About pigmetns - check below chart for excitation/emision chart for GFP pigments - you will see that there is no any above 600nm - its mean " red" light.Almost 65% of them is below 470 and 510nm.

Chlorophyll (both a and c) is a pigment, as is peridinin, the xanthophylls, beta carotene, etc. Zooxanthellae contain several of these, and despite their being colorful, within the zoox they mix and make a golden brown color - the same as in most of the SPS corals on the reefs.

Not all pigments are fluorescent. Put only 400-500nm light over most tanks and you'll see a whole lot of green get reflected, but not much more, especially over SPS, which typically contain non-fluorescent proteins.

Dana Riddle has several series about coral coloration, pigments (both fluorescent and non), chromoproteins, etc, and are great reads, though admittedly very long and technical, so for anyone embarking on that journey, Godspeed

How to Make Corals Colorful, Part One: New Information, With Particular Attention to Blue-Green Fluorescent Pigments
How to Make Corals More Colorful, Part Two: New Information! Green Fluorescent Pigments, Pigment Clades, and Photoconversion from Green to Orange/Red
How to Make Corals More Colorful Part 3 - New Information: Red Fluorescent Pigments: DsRed-type
Coral Coloration: Fluorescence: Part 1
Coral Coloration, Part 2: Fluorescence: Pigments 510 - 565 and Notes on Green Fluorescent Proteins
Coral Coloration, Part 3: Pigments Responsible for Yellow and Orange
Coral Coloration, Part 4: Red Fluorescent Pigments, a Preliminary Report of Effects of Various Environmental Factors and Color Mixing
Coral Coloration, Part 5: Non-fluorescent Chromoproteins (CP-480 to CP-562)
Coral Coloration, Part 6: Non-fluorescent Chromoproteins (CP-568 "“ CP-610) And A Newly Discovered Colorant
Coral Coloration - Part 7: Coral Reflectance, Chromoproteins and Environmental Factors Affecting Non-fluorescent Pigmentation
Coral Coloration, Part 8: Blue and Green Coral Fluorescence: Environmental Factors Affecting Fluorescent Pigmentation
Coral Coloration, Part 9: Tridacna and Other Photosynthetic Clam Coloration, With Observations on Possible Functions
Making Corals Colorful: New Information on Acropora species
Making Corals Colorful: 'Kaede' Fluorescent Proteins

The light serves 2 purposes. First, some is absorbed by the coral, used and spit back out at a higher frequency with less energy. Second, some gets reflected. Both of these combine for what our eyes perceive as color.

You absolutely need to supply the right kind of light for the coral to use it for energy. Period. Lots of lights can handle this. Provided that you do this, then the rest of the light will reflect it as you shine - 10K will reflect differently than 20K... this is personal preference. None of these will look like they did in the ocean where there is typically less blue light - I doubt that many of us would want the colors in the ocean that I have seen.

If you are interested I can provide a handful of reasons why LED don't give quite as good of color to SPS than other light (as judged by long-time hobbyists with a wide breath and depth of experience with different lights and corals), but I don't want to further lead to an argument.

LEDs are more than capable of matching the spectral quality and total output provided by any other light source in the 400-700nm range (outside of which is waste light), that cannot be refuted. Therefore, with said matched spectral quality you can achieve identical coloration properties provided by the other light sources. The main issue is that LED light is not uniform - IE, if I add two cyan LEDs to a small LED cluster that covers a 24"x24" area, even without lenses that light is only going to be hitting so much area due to the directional nature of the light. If a coral or rock shades a part of another coral from that particular LED, it will not hit it and will not be able to absorb or reflect it, and any coloration that would be brought by it won't be. Water refraction will help, but it can only do so much.