Obtaining 700nm light wavelength

[FredFlintstone]

If I had a white light bulb and covered it with the right colour of film (red-ish) will the resulting wavelength be about 700nm?

 

[berkeman]

If I had a white light bulb and covered it with the right colour of film (red-ish) will the resulting wavelength be about 700nm?

I believe so...

https://sites.google.com/a/coe.edu/.../electromagnetic-spectrum/EMSpectrumcolor.jpg

 

[Rive]

The answer for the question is actually a 'yes', but if you would ask about the know-how requested in the title instead, then I would say it's better to buy a 700nm LED from a reliable source.

 

[pinball1970]

I believe so...

https://sites.google.com/a/coe.edu/.../electromagnetic-spectrum/EMSpectrumcolor.jpg
View attachment 223677

yes and no. The "red" part of the spectrum IS 700nm but the reds we see in real life are a mixture. If the film is "red-ish" the resulting wavelength will have a spike at 700nm but some other "ish" will probably be in there be in there. Depends on the film.

 

[pinball1970]

he answer for the question is actually a 'yes', but if you would ask about the know-how requested in the title instead, then I would say it's better to buy a 700nm LED from a reliable source.

LEDs in the UK tend to be a certain temp but that can be made up of different spectral power distributions. D65 is is defined as is TL84 I don't think the SDC or CIE have made their mind up about what CCT or spectral distribution of LEDs are, there are lots of them.

 

[berkeman]

LEDs in the UK tend to be a certain temp but that can be made up of different spectral power distributions. D65 is is defined as is TL84 I don't think the SDC or CIE have made their mind up about what CCT or spectral distribution of LEDs are, there are lots of them.

I think he meant discrete 700nm LEDs, not LED Lamp bulbs...

http://www.newark.com/and-optoelect...MI3I3sgvet2gIVkohpCh1Qtwc0EAAYASAAEgK4W_D_BwE
https://www.mouser.com/Optoelectronics/LED-Lighting/LED-Emitters/_/N-8usfd?P=1yzozrw

 

[pinball1970]

I think he meant discrete 700nm LEDs, not LED Lamp bulbs...

Ah... ok.

 

[Rive]

LEDs in the UK tend to be a certain temp but that can be made up of different spectral power distributions. D65 is is defined as is TL84 I don't think the SDC or CIE have made their mind up about what CCT or spectral distribution of LEDs are, there are lots of them.

The amount of abbreviations required to correctly describe a simple, careless sentence ...

 

[pinball1970]

The amount of abbreviations required to correctly describe a simple, careless sentence ...

i love this site- really friendly science meets the community

CIE- - this the body who specify light International Commission on Illumination

CCT- Colour temperature or correlated colour temp (opps there I go again)

SDC - society of dyers & colourists

D65 artifical daylight

D65 power distribution

https://en.wikipedia.org/wiki/Illuminant_D65#/media/File:SPD_D65.png

TL84 is a standard light in Europe /stores

 

[berkeman]

SDC - society of dyers & colourists

I learn something new every day at the PF!

 

[FredFlintstone]

Thank you all for your input. I'm not sure if the easy solution is colour films such as http://shopwl.com/lighting/lighting-gel/
Using these with well diffused white light and measuring the wavelength or colour warmth until the right frequency is found.

LEDs are certainly be an option, but I think they might be tricky to source at the right energy output levels (80mW/cm²) needed for photobiomodulation - which is my intended use.

 

[berkeman]

Using these with well diffused white light and measuring the wavelength or colour warmth until the right frequency is found.

LEDs are certainly be an option, but I think they might be tricky to source at the right energy output levels (80mW/cm2) needed for photobiomodulation - which is my intended use.

Can you say more about your research? Are you wanting to fine-tune the illumination wavelength(s) in your PhotoBioModulation investigation? Are you wanting to be able to change the illumination wavelength(s) during your investigation? What optical wavelength measurement instrument are you using to document the illumination?

 

[FredFlintstone]

Can you say more about your research? Are you wanting to fine-tune the illumination wavelength(s) in your PhotoBioModulation investigation? Are you wanting to be able to change the illumination wavelength(s) during your investigation? What optical wavelength measurement instrument are you using to document the illumination?

This is first-stage research - just fact finding to see what the options and and what the pros and cons will be. My minimum requirement is a fixed wavelength of, say 800nm with an energy output of 80mW/cm2 at 12 inches distance. LEDs might be the best option for this simple goal. It would be nice to be able to alter the wavelength by adding or subtracting colour films - but I might not be able to tune as I don't want to spend too much time on this project, and I don't own a photo spectrum meter. It's a personal project idea so I can't budget in that kind of hardware.. but I might be able to get use of one.

 

[Rive]

Thank you all for your input. I'm not sure if the easy solution is colour films such as http://shopwl.com/lighting/lighting-gel/
Using these with well diffused white light and measuring the wavelength or colour warmth until the right frequency is found.

I could not find any details on the products what would guarantee that they are some kind of wavelength filters. More likely they are some kind of color filters instead and produces mixed colors, matching with the approach of @pinball1970.

I don't know exactly how biomodulation works, but if it works with mixed colors too, then the it would be OK with a simple LCD monitor.
Somehow I doubt it would work like that, so you might want to search for some wavelength filters (with detailed datasheet, stating the transparency and the wavelength) instead of some basic lighting products

 

[russ_watters]

This is first-stage research - just fact finding to see what the options and and what the pros and cons will be. My minimum requirement is a fixed wavelength of, say 800nm...

How fixed and how wide? Your title says 700nm...

Your best bet may be a narrow-band astronomical hydrogen alpha filter, centered at 656 nm.

 

[FredFlintstone]

I could not find any details on the products what would guarantee that they are some kind of wavelength filters. More likely they are some kind of color filters instead and produces mixed colors, matching with the approach of @pinball1970.

I don't know exactly how biomodulation works, but if it works with mixed colors too, then the it would be OK with a simple LCD monitor.
Somehow I doubt it would work like that, so you might want to search for some wavelength filters (with detailed datasheet, stating the transparency and the wavelength) instead of some basic lighting products

The LCD monitor was not a bad idea but they are not able to put out the amount of energy needed - which is a good thing normally! Yes optical wavelength filters would be better but way more expensive.

 

[FredFlintstone]

How fixed and how wide? Your title says 700nm...

Your best bet may be a narrow-band astronomical hydrogen alpha filter, centered at 656 nm.

I have a few specific wavelengths I'm looking at, but the feasibility of getting one will hopefully apply to others. Right now I'm also looking at 810-850nm. Thing is, it has to be within a limited budget. I will look into your solution but it sounds like it might be out of my reach. Thanks.

 

[FredFlintstone]

How fixed and how wide? Your title says 700nm...

Your best bet may be a narrow-band astronomical hydrogen alpha filter, centered at 656 nm.

Actually, this type of filter looks really good, but costly in the quantity I want it. If only I could get that tech on a continuous length of acrylic or perspex.

 

[Rive]

I have a bad feeling about this project.

Could you please enlighten us if you need a specific color or a specific wavelenght?

 

[FredFlintstone]

I have a bad feeling about this project.

Could you please enlighten us if you need a specific color or a specific wavelenght?

I have been trying to determine the feasibility of producing ANY given wavelength within the near infrared which between 700nm and 900nm. I asked to start with about 700nm (which I referred to as "red-ish") just to narrow the enquiry, presuming that whatever is true of it should be true of other specific wavelengths. I'm not trying to reproduce an exact colour (that's too vague) but as these wavelengths are near infrared I think is OK to use the term colour as a rough approximation when they are in the visible spectrum. So if I have a "red-ish" filter this is approximately 700nm.

I think it would be fairly easy to just get LEDs that are specified at a wavelength - as you already suggested - but the advantage of using film "filters" would be that the wavelength could be changed at will. So. Maybe I just need to do some tests.

 

[Ketch22]

What you are describing as "a specific color of filter" is common practice. Contact a local theatrical supply house or stage equipment retailer. Lighting designers often use Gels to filter the light. The suppliers have swatchbooks very similar to a paint chip book that gives the light spectrum by percentage at a specific Nm that is passed. They use these to design interactions on the stage. It would not be terribly difficult to do a two stage filter. The first gel would filter a color very rich in your desired wavelength. This would also be a composite light that creates a pleasing color. The second filter would then filter the undesirables.
Keep in mind that all of that light that is "filtered" is actually energy that must be absorbed and diffused in the gel. Take too high of a percentage at one time and you can melt your gel.

 

[Tom.G]

Here is a scan of some common CINE color filters. These happen to peak around 625nm. Many of them are down to 10% out-of-band

 

[Rive]

I think is OK to use the term colour as a rough approximation when they are in the visible spectrum. So if I have a "red-ish" filter this is approximately 700nm.

The problem with this is that the term usually defines the required area of expertise. That's why there is that confusion at the start of the topic.

For example, here is a spectrum taken from an LCD monitor:

(source: http://psy1.psych.arizona.edu/~jforster/dmdx/help/lcd-parameters.html )
In terms of 'color', you can get a decent yellow from this monitor without any problems.
But in terms of wavelength, whatever you do you can never, ever get anything around 600nm, for example.

If you need the wavelength, then you need materials with well defined spectrum in the (existing, available) datasheet and no more 'color' please

 

[FredFlintstone]

Here is a scan of some common CINE color filters. These happen to peak around 625nm. Many of them are down to 10% out-of-band

Thank you. I'll take a closer look at this.

 

[FredFlintstone]

What you are describing as "a specific color of filter" is common practice. Contact a local theatrical supply house or stage equipment retailer. Lighting designers often use Gels to filter the light. The suppliers have swatchbooks very similar to a paint chip book that gives the light spectrum by percentage at a specific Nm that is passed. They use these to design interactions on the stage. It would not be terribly difficult to do a two stage filter. The first gel would filter a color very rich in your desired wavelength. This would also be a composite light that creates a pleasing color. The second filter would then filter the undesirables.
Keep in mind that all of that light that is "filtered" is actually energy that must be absorbed and diffused in the gel. Take too high of a percentage at one time and you can melt your gel.

I understand the white lamp could be hot but I'm not sure I understand your last sentence about "take too high a percentage"... how does this relate to heat?

 

[sophiecentaur]

I have a bad feeling about this project.

Could you please enlighten us if you need a specific color or a specific wavelenght?

The right answer to this question depends on the specific requirement. This point really should have been brought up within the first few posts on the thread.

feasibility of producing ANY given wavelength

I suspect that you do not need a specific wavelength (laser source?) but a particular range of wavelengths. You need to be more specific about your requirement. (I am not just been picky here)
I imagine there has been previous work on PhotoBioModulation and those experiments would give an idea of what bandwidth and power flux you need. Have you a good reference for PF to get an idea of what you need? An LED may seem to have a very low power but, once you have passed a 'bright' light source through a narrow filter, you could end up with even less. For high intensity light sources, it's common to use an array of LEDs these days.

 

[FredFlintstone]

The problem with this is that the term usually defines the required area of expertise. That's why there is that confusion at the start of the topic.

For example, here is a spectrum taken from an LCD monitor:
View attachment 223805
(source: http://psy1.psych.arizona.edu/~jforster/dmdx/help/lcd-parameters.html )
In terms of 'color', you can get a decent yellow from this monitor without any problems.
But in terms of wavelength, whatever you do you can never, ever get anything around 600nm, for example.

If you need the wavelength, then you need materials with well defined spectrum in the (existing, available) datasheet and no more 'color' please

I'm trying to understand you, but if you mix light from a red LED and a green LED will you not get yellow light which has a wavelength of approx 600nm, even from an LCD monitor?

 

[Rive]

I understand the white lamp could be hot but I'm not sure I understand your last sentence about "take too high a percentage"... how does this relate to heat?

You need 80mW/cm2. If your filter eliminates 90% of the incoming light and let's through 10% of it at a specific wavelength (range) then you'll have to deal with 720mW/cm2 dissipation on your filter.
If your source has high IR radiation then it's even worse. You might need air cooling for the filters and maybe multiple layers of filtering to keep the dissipation on one layer manageable.

I'm trying to understand you, but if you mix light from a red LED and a green LED will you not get yellow light which has a wavelength of approx 600nm, even from an LCD monitor?

You will see yellow, which will exist as the mixture of some red and green, but if your source has no 600nm then it'll be absolutely without any 600nm.

Colors does add, subtract and mix, but wavelengths does not.

 

[FredFlintstone]

The right answer to this question depends on the specific requirement. This point really should have been brought up within the first few posts on the thread.

I suspect that you do not need a specific wavelength (laser source?) but a particular range of wavelengths. You need to be more specific about your requirement. (I am not just been picky here)

I imagine there has been previous work on PhotoBioModulation and those experiments would give an idea of what bandwidth and power flux you need. Have you a good reference for PF to get an idea of what you need? An LED may seem to have a very low power but, once you have passed a 'bright' light source through a narrow filter, you could end up with even less. For high intensity light sources, it's common to use an array of LEDs these days.

In my second post of this thread I gave the power requirement, around 80mW/cm2.
The wavelength range and power can be obtained from LEDs - this is how most devices in biophotomodulation field are made. But I was hoping it could be obtained by using a white light source and filtered because this would give more flexibility and allow for more wavelength ranges from the same device.

 

[FredFlintstone]

You need 80mW/cm2. If your filter eliminates 90% of the incoming light and let's through 10% of it at a specific wavelength (range) then you'll have to deal with 720mW/cm2 dissipation on your filter.
If your source has high IR radiation then it's even worse. You might need air cooling for the filters and maybe multiple layers of filtering to keep the dissipation on one layer manageable.

Right - got you. Thanks.

You will see yellow, which will exist as the mixture of some red and green, but if your source has no 600nm then it'll be absolutely without any 600nm.
Colors does add, subtract and mix, but wavelengths does not.

Ah, now the lights are coming on, lol. That clears it up for me.

 

[FredFlintstone]

You will see yellow, which will exist as the mixture of some red and green, but if your source has no 600nm then it'll be absolutely without any 600nm.

If I pick up "warm white" light LED bulb (array) from the shop, and the colour warmth is defined as 3000 kelvin (yellow-ish), am I right to think it will most likely have 600nm wavelength in it?

 

[ZapperZ]

If I pick up "warm white" light LED bulb (array) from the shop, and the colour warmth is defined as 3000 kelvin (yellow-ish), am I right to think it will most likely have 600nm wavelength in it?

No.

Zz.

 

[Rive]

If I pick up "warm white" light LED bulb (array) from the shop, and the colour warmth is defined as 3000 kelvin (yellow-ish), am I right to think it will most likely have 600nm wavelength in it?

From here: https://physics.stackexchange.com/q...trum-of-a-light-bulb-and-investigate-how-clos

So, with a warm white LED you have luck on 600nm, but the same time it just won't work for 700nm and longer.

But the actual spectrum will be different for specific products.

Ps.: just one more picture, from one manufacturer: http://www.mightexsystems.com/images/Image/Mightex_LED_wavelength_portfolio_current.jpg

 

[sophiecentaur]

If I pick up "warm white" light LED bulb (array) from the shop, and the colour warmth is defined as 3000 kelvin (yellow-ish), am I right to think it will most likely have 600nm wavelength in it?

Most LEDs used for lighting have fairly continuous spectra so there should be some of everything in there. So they are better sources for biological experiments which work on wavelength and not 'colours' (a strictly human quantity).

I gave the power requirement, around 80mW/cm2.

Oh yes, but what is the wavelength interval needed? That is very relevant, particularly if you are using a filter to select the bandwidth. You need 10 times the power for a filter that's 1/10 of the bandwidth with the same centre wavelength. If you can't think of a reason to find the bandwidth worth considering then just re read the previous sentence. If it doesn't matter then a cheapo (theatrical lighting?) filter would do. 600nm is 'Orange-ish'. Please be more specific about your requirements or you can't get a useful answer.

PS You could always try an under-run filament lamp so that it just glows 'orange hot'. A few Ohms of power resistor in series may well be the cheapest solution.

 

[FredFlintstone]

Oh yes, but what is the wavelength interval needed?

Is this the same thing as frequency? I'm probably looking for 10hz and 40hz

You need 10 times the power for a filter that's 1/10 of the bandwidth with the same centre wavelength.

So if I need 80mW/cm² in the bandwidth of 810nm to 850nm, with a 10% filter I need 800mW/cm²

 

[sophiecentaur]

Is this the same thing as frequency? I'm probably looking for 10hz and 40hz

So if I need 80mW/cm² in the bandwidth of 810nm to 850nm, with a 10% filter I need 800mW/cm²

Is that the bandwidth you need? That would be 5% and so a 10% filter would need twice that (160mW.cm²) with a flat spectrum. But you have confused me. Where did the 810 - 850 nm come from? The requirements are now a total mystery to me.
I was just pointing out that the narrower the filter, the less power is admitted. The power scales with the filter bandwidth if the spectrum happens to be flat. If the bandwidth (i.e. range of) wavelengths is narrow then you would need to start with a more powerful source. (pro-rata). This is why it's so important that the details of the required spectrum for the illumination are important.

PS The frequency you refer to would perhaps be the rate of flickering of the illumination (PhotoBioModulation)? (You can have a band of frequencies or a band of wavelengths and both seem to be relevant here)

 

[davenn]

If I had a white light bulb and covered it with the right colour of film (red-ish) will the resulting wavelength be about 700nm?

So if I need 80mW/cm2 in the bandwidth of 810nm to 850nm, with a 10% filter I need 800mW/cm2

so which do you really need ? something centred on 700nm or something centred on 830nm ?

 

[FredFlintstone]

Is that the bandwidth you need? That would be 5% and so a 10% filter would need twice that (160mW.cm²) with a flat spectrum. But you have confused me. Where did the 810 - 850 nm come from? The requirements are now a total mystery to me.
I was just pointing out that the narrower the filter, the less power is admitted. The power scales with the filter bandwidth if the spectrum happens to be flat. If the bandwidth (i.e. range of) wavelengths is narrow then you would need to start with a more powerful source. (pro-rata). This is why it's so important that the details of the required spectrum for the illumination are important.

PS The frequency you refer to would perhaps be the rate of flickering of the illumination (PhotoBioModulation)? (You can have a band of frequencies or a band of wavelengths and both seem to be relevant here)

Regarding the wavelengths - this is explained in posts 17 and 20 of this thread.

so which do you really need ? something centred on 700nm or something centred on 830nm ?

Please see post 20 of this thread.

 

[davenn]

Please see post 20 of this thread.

so why are you stating 810 - 850nm then ?
hence my Q, which do you really want ?

the clearer you are, the better answers you will get
else you just get everyone confused on what you are really after

 

[FredFlintstone]

so why are you stating 810 - 850nm then ?
hence my Q, which do you really want ?

the clearer you are, the better answers you will get
else you just get everyone confused on what you are really after

I believe I have clearly said that I am looking at the feasibility of producing any wavelength in the near infra red. Not everyone is confused - there has been plenty of good points and suggestions in this thread that have been enlightening and helpful - at least to me. So I'm satisfied, and thanks to all.

 

[Integral]

http://www.seabird.com/products/fluorometers
Are you aware of this line of optical oceanographic instrumentation. Seems that they measure water properties in a manor similar to what you seem to be investigating.

 

[sophiecentaur]

I believe I have clearly said that I am looking at the feasibility of producing any wavelength in the near infra red

I know you have said that but it has no meaning as it stands. There are an infinite number of ways that statement could be taken, You could mean anything from a hot filament with a peak in its spectrum at around 810 - 850nm (a very broad black body spectrum) or a near- monochromatic source that can be tuned to a very narrow band, somewhere between your specified wavelengths. Those two requirements involve totally different solutions.
Just because no one else has pointed this out does not mean it's not relevant. If you could actually tell us what you mean by a source of "any wavelength" then I am sure it can be done. This is why I asked you for a reference to a similar experiment in which, hopefully, the answer would appear. PF threads can be very wide ranging and they are likely to diverge from what the OP wanted. They are not 'chaired' by someone to keep them on track and they often turn into a pleasant chat of members amongst themselves. You want a physical working solution to this that actually does the job you want. So tell us the job and that needs to be more than a shorthand description for a light source. I know you want a 'result' here and I am trying to make sure you get it.

 

[FredFlintstone]

You want a physical working solution to this that actually does the job you want. So tell us the job and that needs to be more than a shorthand description for a light source. I know you want a 'result' here and I am trying to make sure you get it.

Sorry if my initial question caused confusion but I have already clarified these points. My intended application is photobiomodulation (PBM) - which is a branch of medicine that has to do with therapy through light, particularly infrared. Most PBM medical devices use LEDs for this purpose. I was hoping that filtered white light could be used so that multiple wavelengths could be used from a singe device. My purpose for this thread was to gain enough understanding of the different practical issues needed to produce any particular wavelength - or bandwidth - within the near IR spectrum to know which approach is feasible within my budget and timeframe.

I haven't studied Physics and did not have even a rudimentary understanding of light. So, the important take-aways for me so far have been:
1) colour is not the same as wavelength
2) you can't mix two different wavelengths to make another pure wavelength
3) LEDs can be purchased that will produce specific wavelengths, with a given power output
4) certain sources of white light that contain a desired wavelength, if powerful enough, can be filtered using optical filters to obtain a desired wavelength and power output at a desired wavelength

So I now have the knowledge to make some direction decisions. Is there more I could know? Yes, and I'm still interested in hearing creative solutions or corrections to my understanding.

 

[FredFlintstone]

http://www.seabird.com/products/fluorometers
Are you aware of this line of optical oceanographic instrumentation. Seems that they measure water properties in a manor similar to what you seem to be investigating.

Thanks for the link. Interesting gear. However they seem limited to 700nm range unless I'm missing something. Cheers.

 

[sophiecentaur]

Most PBM medical devices use LEDs for this purpose. I was hoping that filtered white light could be used so that multiple wavelengths could be used from a singe device.

Now we're talking. Your list of things you have learned is great and you may now be in a better position to make a good final decision as to which way to go with this.
Advice for the future: provide any forum with a good reference or two in your first post and save a lot of time going round the houses.
So you are interested in replacing LED sources with conventional alternatives? That's a novel thought. They have spent several years in the health business, developing high power LED arrays to replace halogen and other filament lamps. LEDs have many advantages (although, personally I haven't found long life one of them) including cool running of operating theatre lamps.
It could be worth your while approaching some manufactures with your actual requirement and see if they can offer you anything that's near to what you want or need.

 

[Merlin3189]

I wonder why no one suggests a prism?

 

[sophiecentaur]

I wonder why no one suggests a prism?

I wonder about the actual implementation of that idea over a usefully large target area. An interference filter would do the job just as well and the passband characteristic could select the precise band of wavelengths that are required.

 

[Merlin3189]

Yeah, getting enough light into a narrow beam would be difficult. It was what I first thought of - I'd imagined a bunch of cells or even molecules in a test tube.

It did seem to address the cheapness and variable wavelength issues.

It also, very early on, seemed like a good way to find out what was really wanted - colour or wavelength and degree of purity.

I suppose perspective comes into it. people being paid to do research naturally think of narrow band filters or tuneable lasers or anything with an impressive price, but people paying their own bills need to think what they can pick up from the FE for a few $.

 

[sophiecentaur]

I suppose perspective comes into it. people being paid to do research naturally think of narrow band filters or tuneable lasers or anything with an impressive price, but people paying their own bills need to think what they can pick up from the FE for a few $.

From what the OP has told us lately, we are not talking in terms of high accuracy or narrow band spectrum requirements.
Cheaper than all that are the vast number of stage gels that are available but, from what I can find in searches, the pass bands are not published. You would need to have a suitable spectrometer to select which is needed. It would be a tall order for a non- Physicist to implement a DIY spectrometer. It could be worth while approaching the major producers for any information they might have. (I wouldn't mind betting they do have it.
"Variable wavelength" can be achieved with a handful of (cheap) different filters.
I looked up Dichroic Filters and found this link which would probably have what's needed (at a price). Others are probably available.