Change in energy as light passes through air/water

In summary, the conversation discusses the light coming from LED's over an aquarium and the presence of a green tinge in the light. It is questioned whether this is due to the light losing energy as it hits the water, or if it is a result of refraction and scattering of light. It is also suggested that fluorescence from the UV component of the light and substances in the water may be contributing to the green tinge. The discussion concludes that the green tinge is most likely due to fluorescence and it is recommended to change the water if there is a noticeable green tinge.
  • #1
tkyoung75
48
4
Okay, best to provide some background here. I am trying to understand the light coming from the LED's over my aquarium. I have blue moon lights I think at about 540nm and 450nm. Oddly enough, when they are on, there is a green tinge to the light. I had assumed that this was because the light lost energy as it hit the water, therefore lengthening the wavelength. However, as I tried to further prove to myself that this was what was happening I learned that the wavelength of the light decreases as it hits the water.

Up until now, I was of the understanding that the UV light was higher energy, but there is a contradiction in the above. Is it that the UV light is a more 'concentrated' energy, and that the colour change is due to refraction and / or 'wave-spreading' of the more angular incidences of light (they are only 60 degree lights)? Or is it that the light loses colour temperature?

I am guessing that it is a combination:
- the green tinge is from wavelength being spread as it hits at an angle, combined with some prismatic effect bending green light, present in the imperfect light beam, further than it bends the blue.
- The light also loses energy at the surface and as it dissipates through the water.

Please confirm / correct / elaborate
 
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  • #2
I don't know enough about this stuff to answer your question but I can tell you for sure that the range you have is the range of UV that is the very best for causing many substances to fluoresce green or greenish yellow. Possible that's adding to the effect you are seeing (something in the water is fluorescing ?)
 
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  • #3
tkyoung75

Light comes in quanta called photons. Each photon has an energy equal to ##h\nu## that is Planck's constant times frequency. The total light intensity is number of photons times energy of each. As light enters the water, its frequency does not change, it still has the same energy. A certain portion of photons will be reflected at the surface, and as they travel through water, they get absorbed. Neither of this processed changes the energy of individual photons, just their number.
There is also light scattering, that changes of direction of light. (This is what makes the sky blue and sunset red).

540 nm is actually green light. Your LED produces both, blue and green.
The greenish tinge could come as a results of one or more of the following:

Stronger absorption of blue light
Stronger scattering of blue light
Fluorescence

Fluorescence occurs when something absorbes a photon of one energy and re-emits a photon of a lower energy.
Fluorescens is quite common when incident light has short wavelength.

And yes, green light will refract at a slightly different angle then the blue light when entering water.
 
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  • #4
The colour we see is due to the frequency of the light, which does not change. It is the wavelength that changes through different media because the speed of the light is less than c, the speed in empty space. We can safely say that, in these circumstances, there can be no change in the frequency of the light. The wavelength changes as light goes through different media revert to the 'in air' wavelength when it emerges again and when you see it.
If you are getting an apparent change in colour it can either be due to filtering of some of the wavelengths in your lights or fluorescence due to some UV component of your lights and something in your water or the tank walls.
Thick cheap glass has a greenish tinge when you look through the edge of a sheet but your aquarium glass will be nicer quality than that, I would think.
 
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  • #5
tkyoung75 said:
Okay, best to provide some background here. I am trying to understand the light coming from the LED's over my aquarium. I have blue moon lights I think at about 540nm and 450nm. Oddly enough, when they are on, there is a green tinge to the light. I had assumed that this was because the light lost energy as it hit the water, therefore lengthening the wavelength. However, as I tried to further prove to myself that this was what was happening I learned that the wavelength of the light decreases as it hits the water.

Up until now, I was of the understanding that the UV light was higher energy, but there is a contradiction in the above. Is it that the UV light is a more 'concentrated' energy, and that the colour change is due to refraction and / or 'wave-spreading' of the more angular incidences of light (they are only 60 degree lights)? Or is it that the light loses colour temperature?

I am guessing that it is a combination:
- the green tinge is from wavelength being spread as it hits at an angle, combined with some prismatic effect bending green light, present in the imperfect light beam, further than it bends the blue.
- The light also loses energy at the surface and as it dissipates through the water.

Please confirm / correct / elaborate
I have a Marineland model 01G33 fish tank light fixture, with a blue LED moonlight setting.
Visually, and photographed against the white lights, my blue LEDs, run though a 1000 lines/mm diffraction grating, show that they are very, very dirty little lights.
By that, I mean that they emit all the colors of the rainbow, from violet to red.
Of course, they are brightest in the blue region.

moonlight.blue.fish.tank.leds.png

Upper spectrum is from a blue bulb.
Lower spectrum is from a white bulb.​

ps. If there's a green tinge to your water, then it's time to change the water.
 
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  • #6
Sorry, its 450nm and 465nm on the moon channel.
Photo below (strong algae is a sign of good health, although poor nutrient balance which is what I am supposed to be working on :)

Yes, I think the front glass is low iron (mass production ik).

Looks like it must be fluorescing ... amazing ... the organics and ionics in the aquarium.
I put it down to fluorescence as it is cloudy (rather than rayish, for want of a better word), the blue light nearer the bottom (blue light is known to penetrate deeper due to the higher energy) might eliminate 'scattering' as the major factor. Absorption, and fluorescing ... amazing.

I think I recall that the light does include some UV in its spectrum.

Thank you so much for your responses.

For bonus points ... Would it be the short wavelength UV fluorescing (getting chopped) and changed to green, or would it be the the whole spectrum moving along, to a longer wavelength.
 

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  • #7
OmCheeto, I suspected as much. quite a spread for those high efficiency LED's.
Mine are Cree 3W LED's, not sure about the marineland ones but I suspect they are similar.
Actually great image to see. I am not sure if you are aware, but there is a reason the aquarium lights have intensity spots like that, and its called Photosynthetically Active Radiation (PAR), It is the bands of the spectrum that plants use to photosynthesise. Never seen it like that. Brings new fuzzier to memory of my first year physics prac. I have attached the curves from my manufacturer.
As you mention green water, please let me clarify that yes, I am in the process of changing from those dirty 'lignosulfonate' chelates to the purer DTPA / EDTA forms for my aquarium, and cancelling the use of that precipitous MNSO4. I am getting there, give me a break!,
 

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  • #8
tkyoung75 said:
Sorry, its 450nm and 465nm on the moon channel.
It will not be monochromatic. Those figures will relate to the peak wavelengths.
 
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  • #9
sophiecentaur said:
It will not be monochromatic. Those figures will relate to the peak wavelengths.
Actually, according to everything I've read over the last 4 hours, the LEDs are very monochromatic.

Cree apparently makes only one model of blue LED: Royal Blue.
My spectral analysis may be boogered by the deficiencies of optical Bayer filtering in dollar store digital cameras.
Unfortunately, I don't have access to high dollar spectral equipment.

Perhaps I should box up my fish tank lamp, and send it to @Andy Resnick for proper analysis. :biggrin:

ps. There was talk of "remote phosphor LEDs" at the one [graph] website, so I thought maybe Cree put some phosphors into the mix.
So I took my UV light, and placed it over the lamp, and only the white LEDs glowed.
I could also see the my backup optical sensors, aka "my eyes", had fooled me into thinking all of the LEDs looked the same.
I could clearly see that there was no visible phosphor covering the blue LEDs.
 
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  • #10
OmCheeto said:
I have a Marineland model 01G33 fish tank light fixture, with a blue LED moonlight setting.
Visually, and photographed against the white lights, my blue LEDs, run though a 1000 lines/mm diffraction grating, show that they are very, very dirty little lights.
OmCheeto said:
Actually, according to everything I've read over the last 4 hours, the LEDs are very monochromatic.
Cree apparently makes only one model of blue LED: Royal Blue.
My spectral analysis may be boogered by the deficiencies of optical Bayer filtering in dollar store digital cameras.
Unfortunately, I don't have access to high dollar spectral equipment.

Perhaps I should box up my fish tank lamp, and send it to @Andy Resnick for proper analysis. :biggrin:

I'm surprised your measured LED spectrum is so broad- if you send the light through the grating and project against a wall instead of the camera, does the spectrum look that broad to your eye?
 
  • #11
tkyoung75 said:
Oddly enough, when they are on, there is a green tinge to the light. I had assumed that this was because the light lost energy as it hit the water, therefore lengthening the wavelength.
No, this is incorrect. Some energy is lost because some photons are absorbed, but the energy in each photon stays the same. There are just fewer photons making it all the way through.
Also, the energy of a photon depends on the frequency of the photon, not the wavelength. In vacuum, the wavelength is just inversely proportional to the frequency, so you can say longer wavelength <=> lower frequency <=> lower energy. But if you are crossing between different materials, the wavelength will change, and the frequency and energy will stay the same.

tkyoung75 said:
Is it that the UV light is a more 'concentrated' energy, and that the colour change is due to refraction and / or 'wave-spreading' of the more angular incidences of light (they are only 60 degree lights)? Or is it that the light loses colour temperature?
The technical term for 'wave-spreading' is "dispersion". The color change is due to both dispersion and absorption. Dispersion will result in the color changing as you look at different angles and areas, but absorption will filter the color.
 
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  • #12
Andy Resnick said:
I'm surprised your measured LED spectrum is so broad- if you send the light through the grating and project against a wall instead of the camera, does the spectrum look that broad to your eye?

One moment, please...

[an hour later]

Oh. My. God.

Bathroom science...
 
  • #13
OmCheeto said:
the deficiencies of optical Bayer filtering
How were you thinking of spectral analysis with Bayer filtering?
 
  • #14
sophiecentaur said:
How were you thinking of spectral analysis with Bayer filtering?

Dollar store scientist?
:confused:
 
  • #15
OmCheeto said:
Dollar store scientist?
:confused:
Tell me a bout "dollar store scientist".
The analysis in a camera is very similar to the analysis by the eye (hardly surprising). It uses just three wide band analysis curves which cannot tell the difference (and nor can your eye) between a monochromatic source and a wideband source with the same colour (metemeric match - see link). If you actually know that the source is monochromatic then three RGV values can identify the wavelength but you need to know it's monochromatic before you can do that.
But I could accept the results of Andy [EDIT with apologies: damned autocorrect!] Resnick's suggested spectroscope as evidence one way or the other.
Not long ago I bought a cheapo spectroscope (sold mainly for lapidary identification). It is great fun to examine (qualitatively) the spectra of many light sources. It could be good for some optical filters too.
 
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  • #16
Khashishi said:
The technical term for 'wave-spreading' is "dispersion". The color change is due to both dispersion and absorption. Dispersion will result in the color changing as you look at different angles and areas, but absorption will filter the color.
Of course. Thanks Khashishi.

have been reading From LED lights
OmCheeto said:
Cree apparently makes only one model of blue LED: Royal Blue.
Revised Spec - Optical power: 40 pcs 3W Bridgelux Bxce/Bxcd LED
 
  • #17
Andy Resnick said:
I'm surprised your measured LED spectrum is so broad- if you send the light through the grating and project against a wall instead of the camera, does the spectrum look that broad to your eye?
Took a nap, as doing such usually reboots my brain.

I've decided there's no way for me to inexpensively focus the light from the bulb. ie, less than a whole roll of duct tape.
I've also decided I'm chasing a ghost. I have no idea who made my blue LEDs, nor what their spectrum should be.
It's tkyoung who has the Cree lamps.
 
  • #18
OmCheeto, My Aquarium Light is a DSunY, with Bridgelux LED's. Sorry for the confusion. Did you check the spectrum without the filtering? Did it change?

I have just done a 50% water change, including makeup salts, and there is a significant change in fluorescence. This is an awesome learning. Not only does it show the amount of organic buildup, but with a bit more research I might be able to pinpoint the organic by the colour of the light. Thank you so much!

Before photo:
[NOPARSE][PLAIN]http://www.gentlespring.com.au/20160728_095436.jpg[/NOPARSE] [Broken]

After photo:
[NOPARSE][PLAIN]http://www.gentlespring.com.au/20160729_164242.jpg[/NOPARSE] [Broken]

Example Luminescence: Absorption/Emmitance Spectra (mine is not this one, being green)
[NOPARSE]http://www.gentlespring.com.au/Screen [Broken] Shot 2016-07-29 at 5.20.45 PM.png[/PLAIN] [Broken][/NOPARSE]

Source:
http://www.biotek.com/resources/articles/monitoring-of-algal-growth-using-intrinsic-properties.html
 
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  • #19
Interesting. A picture is worth a thousands words. Yes, it is possible for fluorescence to create photons of lower energy. Maybe that's happening here.
 
  • #20
tkyoung75 said:

Here's a somewhat more laymanish site that describes the effect:

Red fluorescence of algal cells is activated by excitation with blue light. This signal is weak when compared to the scattered green light and therefore not usually visible by eye. [ref]

I'm an expert in laymanology.
Oh! And something I might be able to do!

Measuring water fluorescence
Unlike apparent characteristics of water, such as its colour and transparency, fluorescence is not usually visible by eye when looking at the sea or a lake. This is due to the weakness of the signal, when compared to the green backscattered light. To make fluorescence visible we have to reach into our bag of tricks.

I've an appointment with the river in 30 minutes. Perhaps I'll collect some indigenous algae samples.
 
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  • #21
Can't you try using a blue laser? Than it is clear if it is fluorescenes or not causing the green colour..
 
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  • #22
OmCheeto said:
Here's a somewhat more laymanish site that describes the effect:

Red fluorescence of algal cells is activated by excitation with blue light. This signal is weak when compared to the scattered green light and therefore not usually visible by eye. [ref]

I'm an expert in laymanology.
Oh! And something I might be able to do!

Measuring water fluorescence
Unlike apparent characteristics of water, such as its colour and transparency, fluorescence is not usually visible by eye when looking at the sea or a lake. This is due to the weakness of the signal, when compared to the green backscattered light. To make fluorescence visible we have to reach into our bag of tricks.

I've an appointment with the river in 30 minutes. Perhaps I'll collect some indigenous algae samples.
OmCheeto,
Sorry to not respond sooner, I have pondered.
The backdrop on the aquarium is black so that probably helps.
To my logical brain, since energy is equivalent to mass, it seems that some photons "pass" through the interface at a decreased wavelength (a net decrease in energy), and then some of what that gets through "excites" the algae, which absorbs it and "emits it at an increased wavelength (further decrease in energy).
I now have a UV light on the supply pipe. There for a multitude of reasons, perhaps water clarity and light efficiency will prove to be one of them.

I would like to know more about the experiment you have in mind ... (to see for yourself?) at your leisure!
Bear in mind that I have a reasonable amount of plants, and I fertilise the aquarium, so it may take effort to get the fluorescence. Unless, of course, you are checking the water quality of the river?
 
  • #23
tkyoung75 said:
To my logical brain, since energy is equivalent to mass, it seems that some photons "pass" through the interface at a decreased wavelength (a net decrease in energy), and then some of what that gets through "excites" the algae, which absorbs it and "emits it at an increased wavelength (further decrease in energy).

Light does not lose energy upon passing through an interface just because the wavelength changes.
 
  • #24
Drakkith said:
Light does not lose energy upon passing through an interface just because the wavelength changes.
Didn't say that it does! In fact, my understanding is that the decreased wavelength = increase in energy, The net decrease (referred) therefore being due to energy donated by those 'photons' rejected at the interface. If you know better I would love to hear a better explanation!
 
  • #25
tkyoung75 said:
In fact, my understanding is that the decreased wavelength = increase in energy, The net decrease (referred) therefore being due to energy donated by those 'photons' rejected at the interface. If you know better I would love to hear a better explanation!

The correct explanation is that the energy doesn't change as the light passes through the interface. The dependence of energy on wavelength only applies if the light stays in the same medium, not when it enters a different medium. If you are looking at light passing through various interfaces between mediums you are better off using the frequency vs energy relationship, since the frequency of the light doesn't change.
 
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  • #26
Of course ... I should know that. Thank you Drakkith.
 
  • #27
tkyoung75 said:
I would like to know more about the experiment you have in mind ... (to see for yourself?) at your leisure!

I can't remember exactly what it was, but I'm sure it had to do with illuminating my tank with light on the blue end of the spectrum, that contains no green, to see if I could see any fluorescence.

Unfortunately, I have no such light sources. Even my "black" UV light has a strong green emission band.

Below is a collection of spectral emissions tests I did in February, with nearly every type of light bulb I had in the house.
cd-spectrum-experiments-png.96293.png

image created by reflecting light off of an old AOL cd​

I redid the measurement of my blue LED, comparing it to my CFL black light spectrum, and it looks like the blue LED runs from Orange to Violet.

blue.led.vs.cfl.mercury.vapor.black.light.2016.08.08.png

image created through 1000 lines/mm linear diffraction grating
nm wavelengths are measured, using the 579 & 404.7 nm published mercury emission values as reference.​

I believe I "saw" red the last time I did this, but it's just very dim orange.

tkyoung, you are going need to get diffraction grating to guarantee your lamps are not emitting green light. Otherwise, you're just guessing as to what is going on.
 
  • #28
tkyoung75 said:
some photons "pass" through the interface at a decreased wavelength (a net decrease in energy)

The point has already been made that Wavelength and Energy are not related because wavelength will change as EM travels through a medium. Light doesn't change colour as it goes through glass, for instance, although the wavelength decreases. It is the Frequency that governs the photon energy and frequency cannot change at an interface because you need phase continuity. Most scattering of photons is 'elastic' (Raleigh) and the photons do not change energy. Raman scattering involves some energy being lost during the collision and will produce a lower energy photon. This is a totally non coherent thing and you cannot get a coherent wave from the process - a 'ray' cannot change colour.
 
  • #29
OmCheeto said:
Below is a collection of spectral emissions tests I did in February, with nearly every type of light bulb I had in the house.
Those pictures are very confusing to me. I wonder how you obtained them. The output from a spectrometer / spectrograph should show the same wavelength ('colour') for the same direction, whatever the source. In the Enlarger Bulb picture you have a broad strip of 'Cyan'?? which overlaps the blues and greens in other pictures and the white led bulb shows yellow where there is red on other strips. I wonder what system you are using but it looks to me as if your spectrometer must have more than one order of diffraction (?) and giving you an overlap. This could perhaps explain the broad Cyan (=Green + Blue) bar which just shouldn't be there if you are really producing a true angle / wavelength display.
The 'black light' picture is very overexposed at the peak of the spectrum so it's hard to see what 'colour' the peak would be at.
 
  • #30
sophiecentaur said:
Those pictures are very confusing to me. I wonder how you obtained them.
With a cardboard box, an AOL cd, and a dollar store camera.
red-neck-spectrometer-png.96274.png


The output from a spectrometer / spectrograph should show the same wavelength ('colour') for the same direction, whatever the source. In the Enlarger Bulb picture you have a broad strip of 'Cyan'?? which overlaps the blues and greens in other pictures and the white led bulb shows yellow where there is red on other strips. I wonder what system you are using but it looks to me as if your spectrometer must have more than one order of diffraction (?) and giving you an overlap. This could perhaps explain the broad Cyan (=Green + Blue) bar which just shouldn't be there if you are really producing a true angle / wavelength display.
Each of the 7 spectrums was collected independently, so the alignment was done afterwards.
That experiment was done in February, before I received my diffraction grating slides.
[ref: PF, Determine emission spectrum of an LED, post #12]
And as Andy mentioned:
Andy Resnick said:
CD/DVD are not transmissive gratings and have curved 'slits', complicating everything.
So those images are more qualitative than quantitative.

The 'black light' picture is very overexposed at the peak of the spectrum so it's hard to see what 'colour' the peak would be at.
That image was taken last night, with both sources aligned vertically, and the camera was about 23 feet away.
I would have to take multiple pictures, at different exposure settings, to get "visual" colors to come out correctly.
I was more interested in determining the frequency range of the LED, which is why I chose the mercury vapor lamp as reference.

Actually, this new camera is kind of cool, as it records more than just the date:
August 8, 2016 9:55 PM
4608 x 3456, 5 MB, JPEG
ISO 400, 9mm, 0 ev, f/3.3, 8.0s​

I wonder if from those type numbers, and multiple exposures, I could determine the relative intensity at each wavelength. hmmmm...

ps. I have no clue what "0 ev" means. Actually, I don't know what "ISO 400" means either. All I remember is that ISO 1600 is more light sensitive than ISO 400. Actually, the only thing I understand is "8.0s". Smaller f-stops just means the iris is bigger, and let's in more light. (<-- how a layman interprets f-stops) Which kind of reminds me of people making fun of "measurement systems" in "Random Thoughts" a few weeks back. As I decided that "visual magnitude" must have been invented by a mad man: "Dimmer stars have higher numbers". :confused: But then I researched the origin of the concept, and decided that it made quite a bit of sense.
 
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  • #31
OmCheeto said:
With a cardboard box, an AOL cd, and a dollar store camera.
You deserve a medal for ingenuity and entertainment! Very pretty and it needs some 'analysing, I think.
I know people use CDs as gratings but I think there must be something wrong here. Assuming you have the same amount of throw on your system, the spacings of the spectral components should be the same but there is Yellow on the LED white which has gone for the strip. Perhaps you are not starting with a narrow vertical slot. That could account for much of what I am not happy with - the Cyan band near the top. You shouldn't ever see Cyan without green and blue. There must be an overlap giving a mix of blue and green over a broad band. Have another go with the system, making sure you have a narrow slot and collimated light.
Yes I agree that the Magnitude scale is the wrong way up. They got it wrong - same as the sign of the charge on an electron haha. But we can cope!
 
  • #32
sophiecentaur said:
...Have another go with the system, making sure you have a narrow slot and collimated light.
...
Umm... no. This is not my problem. But you did trigger an idea, which precludes tkyoung from having to wait 2 weeks for diffraction grating, as I now perceive this as more a qualitative, rather than quantitative problem. tk just needs to know if there is "green" in the source light.

Low and behold:

cd.dollar.store.spectrum.png

an old CD will do the trick.
 

What is the difference in energy as light passes through air and water?

The main difference in energy as light passes through air and water is due to the different refractive indices of the two mediums. Air has a refractive index of approximately 1, while water has a refractive index of 1.33. This means that light travels slower in water, resulting in a change in energy.

How does the change in energy affect the speed of light?

The change in energy as light passes through air and water also affects the speed of light. As mentioned, light travels slower in water due to its higher refractive index. This change in speed can also result in a change in the direction of the light, known as refraction.

Does the change in energy affect the color of light?

Yes, the change in energy as light passes through air and water can affect the color of light. This is because different colors of light have different wavelengths and frequencies, which can be affected by the change in speed and direction of light as it passes through different mediums.

What other factors can affect the change in energy as light passes through air and water?

Apart from the refractive index of the mediums, other factors that can affect the change in energy as light passes through air and water include the angle of incidence, the temperature and pressure of the mediums, and the composition of the mediums (such as the presence of impurities).

How is the change in energy of light through air and water relevant in everyday life?

The change in energy of light through air and water is relevant in many aspects of everyday life, such as in the functioning of lenses in glasses and cameras, the refraction of light in water bodies, and the phenomenon of mirages. It is also important in understanding the behavior of light in different environments and its impact on our perception of the world.

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