What happens to Spectrum when we dim our lights?

Ok, so let's see if this is possible, but I'd like to hear from any of you (civil discussion) regarding spectrum of lights when we dim.

I think that when you dim the lights on the LED's the spectrum changes like with HID lighting, I mean spectrum is spectrum and light is light right? A lot of the pre made lights we all buy/can buy nowadays have dimmers built in, in some way or another. Many companies go as far as to use this as a selling point. We often get advice when asking about new lights to get more than we need but get a dimmer and it will saves us $$ down the road if we plan to expand, shit I have myself given that advice to people many times. But in growing more with LED's this year I have started to notice a few things and have a hunch on something regarding this subject, so just wondering if this have been beaten to death already, and if so where the info is, or if anyone else has info regarding this. I think in certain circumstances dimming the lights will change the spectrum in a way that would not be beneficial to the grow. I am not trying to start a pissing match here, I feel this is an important aspect of using our lights and if there can be something new to learn that we can all benefit from discussing this.

Make sense? Thoughts?

Didn't notice any spectrum change when dimming...i only noticed it with raising the lights, the more you raise the more spectrum shifts to red

waynejohn said:

Didn't notice any spectrum change when dimming...i only noticed it with raising the lights, the more you raise the more spectrum shifts to red

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Did you test it thought or just go by visual? I don't care either way just trying to clarify. Thanks for chiming in

waynejohn said:

Didn't notice any spectrum change when dimming...i only noticed it with raising the lights, the more you raise the more spectrum shifts to red

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If there's a change in spectrum "raising "the light shouldn't there be one lowering it??

vertnugs said:

If there's a change in spectrum "raising "the light shouldn't there be one lowering it??

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@Evil-Mobo

You can lower the lights only up to a certain point...i noticed it on my 5000k 90cri...i use a lux meter to calculate ppfd and it shows the spectrum color quite correct...at 30-35cm(12-14") 3000k is +-1% 3000k and 5000k is 5000k +-1%...when i raise the lights to 60 cm the meter displays 4700-4800k...at 90cm it's around 4600...with 3000k it's less change with height...it never goes under around 2850k

I know this isn't the best way to measure it probably but i believe the numbers are somewhere in the ballpark

As for why this happens i think it has something to do with blue photons losing their energy over greater distances but really not my area of expertise...i'm sure one of the led gurus around here could explain this much better

waynejohn said:

@Evil-Mobo

You can lower the lights only up to a certain point...i noticed it on my 5000k 90cri...i use a lux meter to calculate ppfd and it shows the spectrum color quite correct...at 30cm 3000k is +-1% 3000k and 5000k is 5000k +-1%...when i raise the lights to 60 cm the meter displays 4700-4800k...at 90cm it's around 4600...with 3000k it's less change with height...it never goes under around 2850k

I know this isn't the best way to measure it probably but i believe the numbers are somewhere in the ballpark

As for why this happens i think it has something to do with blue photons losing their energy over greater distances but really not my area of expertise...i'm sure one of the led gurus around here could explain this much better

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Thanks for the reply. I was trying to ask my question as non confrontational as possible, seriously just after some solid info, to see if my findings would tend to be correct or be an issue with something I did myself.

On my phone so was replying to you and vertnung at the same time, he asked about height...i think you raised a good question and am also curious to know the answer...there is also a factor of temperature of chip...from my limited knowledge the higher the phosporous coating gets the more spectrum shifts to red...would be interesting to see the results of spectrum analysis with different chips at 700mA and 1400mA

waynejohn said:

On my phone so was replying to you and vertnung at the same time, he asked about height...i think you raised a good question and am also curious to know the answer...there is also a factor of temperature of chip...from my limited knowledge the higher the phosporous coating gets the more spectrum shifts to red...would be interesting to see the results of spectrum analysis with different chips at 700mA and 1400mA

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Yeah I agree but I don't have even a par meter let alone a sphere to test with LOL

Lol me neither but i see a lot of apogees and spheres on this forum so only matter of time i gues till someone does it...in cree datasheet the spectral chart is at 2100mA...i would be curious to see the same chart at 700mA, will probably not be a huge difference but i suspect it could shift a bit to the blue side

waynejohn said:

Lol me neither but i see a lot of apogees and spheres on this forum so only matter of time i gues till someone does it...in cree datasheet the spectral chart is at 2100mA...i would be curious to see the same chart at 700mA, will probably not be a huge difference but i suspect it could shift a bit to the blue side

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This is what I want to know because I believe the same and that the shift to blue caused me non desirable tighter node spacing and shorter plants. So at least now if I'm looney tooney on this the looney bin isn't empty

Lol there is always comfort in company but i think we actually might be correct in this case...or at least we are somewhere on the right track...we need someone with the proper tools and a will to experiment

waynejohn said:

Lol there is always comfort in company but i think we actually might be correct in this case...or at least we are somewhere on the right track...we need someone with the proper tools and a will to experiment

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Hopefully that someone pops up

2 different subjects here isn't it?

"Dimming" vs "light height" giving a change in spectrum at certain levels?

Curious about the "dimming" of the driver myself.LED is still new to me so i know nadda....but i would think the led would act in the same manner of an hps no?....if i dim my lumatek through all 4 settings i see 4 different changes in spectrum.

an other question: a light with a 1750Ma driver (i.e) does have the same efficiency/spectrum/ppf etc dimmed at 1400mA... than a light with a 1400mA driver!? sry in advance I'm not sure of my english cause too many facts in just one question!!

PilouPilou said:

an other question: does a light with a 1750Ma (i.e) driver have the same efficiency/spectrum/ppf etc dimmed at 1400mA... than a light with a 1400mA driver!? sry in advance I'm not sure of my english cause too many facts in just one question!!

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Good question and I was about to add this to the discussion myself.

My 5 cents worth, we are talking about a quantum event at the P/N boundary that can only occur once the diode threshold resistance is breached @ min drive voltage, after this point the amount of light output is down to the amount of electrons crossing the pn junction which equates to drive current in leds. The heat is a result of 'lost photons' being emitted back into the led substrate as opposed to out from its surface, so the whole light 'temp' issue is one from incandescent bulbs heated element, or the excitement of the plasma with flouro's. Basically leds are not heaters that emit light, they are light emitters that give off heat.

freemanjack said:

My 5 cents worth, we are talking about a quantum event at the P/N boundary that can only occur once the diode threshold resistance is breached @ min drive voltage, after this point the amount of light output is down to the amount of electrons crossing the pn junction which equates to drive current in leds. The heat is a result of 'lost photons' being emitted back into the led substrate as opposed to out from its surface, so the whole light 'temp' issue is one from incandescent bulbs heated element, or the excitement of the plasma with flouro's. Basically leds are not heaters that emit light, they are light emitters that give off heat.

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As for me myself I am not interested in the heat debate. So how would what you state affect (or not) spectrum of the source of light? That's what I want to know.............

PilouPilou said:

an other question: a light with a 1750Ma driver (i.e) does have the same efficiency/spectrum/ppf etc dimmed at 1400mA... than a light with a 1400mA driver!? sry in advance I'm not sure of my english cause too many facts in just one question!!

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I think if both drivers have the same efficiency then the efficiency of chips/spectrum/ppf should be exactly the same

This could also have to do with light directionality: is the spectrum the same over a cobs whole foot print? I have a feeling that the blue light that bleeds thru the phosphor is more directional, tends to go more straight down than the light that is emitted from the phospor. Or that the hotspot directly under a cob is higher in blue and that when you measure at a distance its not as easy to have it exactly aligned under a cob as it is when youre closer.
Blue light and UV from the sun does get abrsorbed by air but i doubt this is whats happening here: if blue light suffered that much from a foot of air there would be none on the earths surface.
Its also teue that specteum changes with drive current, theres tables about this in most cob datasheets. I think i heard it goes up (as in bluer) the harder you drive it but the change is negligble.
Also if this about directionality you can also pose the question: does spectrum change with optics? I believe heard someone here saying that lenses turns the light redder but im not sure.

I propose the following experiment: measure the spectrum on half drive current at the height where you get aprox 50000lux. Then double drivecurrent and raise the light until again you get aprox 50000lux and you measure the spectrum again. Compare the results and see what you get.
Also: if measured in a reflective tent it might be due to tent reflecting wavelengths at different efficiency.
Or simply your meter: the response to blue may differ depending on light intensity. The above experiment should be able to tell you whether.