3 ms·

Another question: (d) How much does the precise wavelength matter? The study used 670nm but also mentions the range 650-1000nm. Lots of red-light gadgets are a

Another question: (d) How much does the precise wavelength matter? The study used 670nm but also mentions the range 650-1000nm. Lots of red-light gadgets are available on Amazon but how do you verify the wavelength? I was thinking of an optical spectrum analyzer[1] but at $28,000 they are shockingly expensive. Even with raw LEDs bought from a reliable electronics distributor like Digi-Key, it would be nice to be able to measure it somehow. [1] https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=5276 https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=52...

cycomanic 6y ago
I suspect you do not need to use 670nm exactly, however I suspect you need to be above 650nm. Note that many red LEDs are at a lower wavelength (~630nm). So you need to search for deep red or by wavelength. You can use a OSA, but yes they are expensive. Spectrometers are typically cheaper, but still expensive (you could go to a university optics group and ask them if they could measure it for you). That said if you buy from a reputable source you should get the right wavelength. If you are trying this out be careful with the brightness.
- joezydeco 6y ago
  Instead of trying to emit 670nm, why not just use a wide spectrum source and a 670nm bandpass filter?
  - cleansingfire 6y ago
    Like the sun and your closed eyelids. Light transmission goes up with wavelength https://www.spiedigitallibrary.org/journals/journal-of-biomedical-optics/volume-16/issue-06/067011/Measuring-and-predicting-eyelid-spectral-transmittance/10.1117/1.3593151.full?SSO=1 https://www.spiedigitallibrary.org/journals/journal-of-biome... (see figure 5.) To speculate, perhaps we have evolved to benefit from closing our eyes in the sun.
    - joezydeco 6y ago
      That's a great connection. If it's that simple (and explained by human evolution), that would be awesome.
GeorgeRichard 6y ago
You might find this of interest - it seems to be a cottage-industry spectrometer selling for £67: "The i-Phos can see wavelengths from approximately 420 - 980nm and their relative (though not their absolute) intensities." http://chriswesley.org/spectrometer.htm http://chriswesley.org/spectrometer.htm
monkeycantype 6y ago
Shouldn't it be quite cheap to determine the frequency using a prism, using the angle of refraction? I think you should be able to use known missing frequencies in sunlight to calibrate your set up. Back in a minute going for duckduckgo
- monkeycantype 6y ago
  So it looks like you need a bit more than a prism to see Fraunhofer lines, but there seem to be online description of how to do it with a with a prism and a CD, maybe you don't even need a prism, there seem to be 'make your own spectroscope' tutorials than mention building one with cereal box, and maybe a lens of some kind
  - mrob 6y ago
    The D line is probably more easily seen in a colored flame made by adding salt water to an alcohol-burner flame: https://en.wikipedia.org/wiki/Emission_spectrum#/media/File:Cmglee_Cambridge_Science_Festival_2016_sodium_lines.jpg https://en.wikipedia.org/wiki/Emission_spectrum#/media/File:...
    - monkeycantype 6y ago
      that sounds like a project to do with my kids, thanks : )
mindviews 6y ago
I got one of these $25 kits in a physics class that gives you the eyeball version of the fancy digital spectrometer: https://shop.sciencefirst.com/starlab/kits/5800-cardboard-spectrometer-single.html https://shop.sciencefirst.com/starlab/kits/5800-cardboard-sp...
Renaud 6y ago
Most LED have their wavelength in their datasheet. Just select one that has the one you are looking for, it's going to be cheaper and easier than getting an expensive or inaccurate spectrometer. For instance, this classic one is at 660nm: https://www.mouser.com/ProductDetail/Lumex/SSL-LX5093SRD-D https://www.mouser.com/ProductDetail/Lumex/SSL-LX5093SRD-D
joshvm 6y ago
You can get a 1nm resolution "science grade" spectrometer for under £1k - I used to design them [1]. You can also buy used ocean optics kit for very reasonable prices on eBay (a few hundred for a USB2000 if you wait). Or make your own? It'll probably be good enough https://publiclab.org/w/spectrometry https://publiclab.org/w/spectrometry ThorLabs also sell cheaper spectrometers by the way. You don't need a spectrum analyser with seven significant figures! https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=3482 https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=34... You can also get light testing devices used for film/industrial illumination https://www.sekonic.com/color-meter/c700 https://www.sekonic.com/color-meter/c700 (about 1.5-2k) Or even single chip spectrometers with broad 20nm resolution from Hamamatsu (about £400 on group gets). https://groupgets.com/manufacturers/hamamatsu-photonics/products/c12880ma-micro-spectrometer https://groupgets.com/manufacturers/hamamatsu-photonics/prod... [1] https://is-instruments.com/products/miniature-spectrometer/ https://is-instruments.com/products/miniature-spectrometer/
kaybe 6y ago
We like these (or rather, the whole line): https://www.avantes.com/products/spectrometers/compactline/item/1236-avaspec-mini-cl-2048 https://www.avantes.com/products/spectrometers/compactline/i... You can get them used for below 1000$, eg this listing: https://www.ebay.com/itm/Avantes-Compactline-Avaspec-Mini-/324145546928 https://www.ebay.com/itm/Avantes-Compactline-Avaspec-Mini-/3...

cycomanic 6y ago

I suspect you do not need to use 670nm exactly, however I suspect you need to be above 650nm. Note that many red LEDs are at a lower wavelength (~630nm). So you need to search for deep red or by wavelength. You can use a OSA, but yes they are expensive. Spectrometers are typically cheaper, but still expensive (you could go to a university optics group and ask them if they could measure it for you). That said if you buy from a reputable source you should get the right wavelength. If you are trying this out be careful with the brightness.

joezydeco 6y ago
Instead of trying to emit 670nm, why not just use a wide spectrum source and a 670nm bandpass filter?
- cleansingfire 6y ago
  Like the sun and your closed eyelids. Light transmission goes up with wavelength https://www.spiedigitallibrary.org/journals/journal-of-biomedical-optics/volume-16/issue-06/067011/Measuring-and-predicting-eyelid-spectral-transmittance/10.1117/1.3593151.full?SSO=1 https://www.spiedigitallibrary.org/journals/journal-of-biome... (see figure 5.) To speculate, perhaps we have evolved to benefit from closing our eyes in the sun.
  - joezydeco 6y ago
    That's a great connection. If it's that simple (and explained by human evolution), that would be awesome.

GeorgeRichard 6y ago

You might find this of interest - it seems to be a cottage-industry spectrometer selling for £67: "The i-Phos can see wavelengths from approximately 420 - 980nm and their relative (though not their absolute) intensities." http://chriswesley.org/spectrometer.htm http://chriswesley.org/spectrometer.htm

monkeycantype 6y ago

Shouldn't it be quite cheap to determine the frequency using a prism, using the angle of refraction? I think you should be able to use known missing frequencies in sunlight to calibrate your set up. Back in a minute going for duckduckgo

monkeycantype 6y ago
So it looks like you need a bit more than a prism to see Fraunhofer lines, but there seem to be online description of how to do it with a with a prism and a CD, maybe you don't even need a prism, there seem to be 'make your own spectroscope' tutorials than mention building one with cereal box, and maybe a lens of some kind
- mrob 6y ago
  The D line is probably more easily seen in a colored flame made by adding salt water to an alcohol-burner flame: https://en.wikipedia.org/wiki/Emission_spectrum#/media/File:Cmglee_Cambridge_Science_Festival_2016_sodium_lines.jpg https://en.wikipedia.org/wiki/Emission_spectrum#/media/File:...
  - monkeycantype 6y ago
    that sounds like a project to do with my kids, thanks : )

mindviews 6y ago

I got one of these $25 kits in a physics class that gives you the eyeball version of the fancy digital spectrometer: https://shop.sciencefirst.com/starlab/kits/5800-cardboard-spectrometer-single.html https://shop.sciencefirst.com/starlab/kits/5800-cardboard-sp...

Renaud 6y ago

Most LED have their wavelength in their datasheet. Just select one that has the one you are looking for, it's going to be cheaper and easier than getting an expensive or inaccurate spectrometer. For instance, this classic one is at 660nm: https://www.mouser.com/ProductDetail/Lumex/SSL-LX5093SRD-D https://www.mouser.com/ProductDetail/Lumex/SSL-LX5093SRD-D

joshvm 6y ago

You can get a 1nm resolution "science grade" spectrometer for under £1k - I used to design them [1]. You can also buy used ocean optics kit for very reasonable prices on eBay (a few hundred for a USB2000 if you wait). Or make your own? It'll probably be good enough https://publiclab.org/w/spectrometry https://publiclab.org/w/spectrometry ThorLabs also sell cheaper spectrometers by the way. You don't need a spectrum analyser with seven significant figures! https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=3482 https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=34... You can also get light testing devices used for film/industrial illumination https://www.sekonic.com/color-meter/c700 https://www.sekonic.com/color-meter/c700 (about 1.5-2k) Or even single chip spectrometers with broad 20nm resolution from Hamamatsu (about £400 on group gets). https://groupgets.com/manufacturers/hamamatsu-photonics/products/c12880ma-micro-spectrometer https://groupgets.com/manufacturers/hamamatsu-photonics/prod... [1] https://is-instruments.com/products/miniature-spectrometer/ https://is-instruments.com/products/miniature-spectrometer/

kaybe 6y ago

We like these (or rather, the whole line): https://www.avantes.com/products/spectrometers/compactline/item/1236-avaspec-mini-cl-2048 https://www.avantes.com/products/spectrometers/compactline/i... You can get them used for below 1000$, eg this listing: https://www.ebay.com/itm/Avantes-Compactline-Avaspec-Mini-/324145546928 https://www.ebay.com/itm/Avantes-Compactline-Avaspec-Mini-/3...