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Looking for material that will only let UV pass through — Parallax Forums

Looking for material that will only let UV pass through

kf4ixmkf4ixm Posts: 529
edited 2012-02-10 12:57 in General Discussion
Good morning all, does anyone know of a material that will let UV (a, b or c) only light/radiation to pass through? after a few google searches, all i can find metioned is lenses for cameras, which are very expensive. im just looking for something to put in front of a uv led and use the led in reverse-bias mode as a home-brew uv sensor. any help is greatly appreciated!

Comments

  • LeonLeon Posts: 7,620
    edited 2011-02-08 06:46
    I'd buy a UV sensor, it'll be much easier.
  • ElectricAyeElectricAye Posts: 4,561
    edited 2011-02-08 07:31
    You might want to have a look at UV bandpass interference filters. You can find them new at edmundoptics.com or try this guy on ebay:

    http://stores.ebay.com/BJOMEJAG-EBUYER-STORE/Ultra-Violet-Filters-/_i.html?_fsub=9&_sid=8343593&_trksid=p4634.c0.m322

    If you don't see what you want, you can ask him, too.

    EDIT: I should add that what the ebay dude sells is also new, but they are over runs or small defective items from his manufacturing plant.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2011-02-08 08:23
    Are you sure you even need a filter? An LED used as a sensor will not be sensitive to wavelengths longer than what it emits (reference).

    -Phil
  • kf4ixmkf4ixm Posts: 529
    edited 2011-02-08 08:37
    Phil Pilgrim (PhiPi) wrote: »
    Are you sure you even need a filter? An LED used as a sensor will not be sensitive to wavelengths longer than what it emits (reference).

    -Phil
    well, from what i've tested with (radio shack uv led's), the uv led's seem to be somewhat sensitive to ambient light (indoors incandesant). not by much though. i do read some voltage from them when testing indoors. i suppose i could use some sort of filtering, with a resistor or comparator, but was hoping there was some sort of material available that would accomplish this.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2011-02-08 09:04
    You may have some UV light indoors, or the RadioShack "UV" LED may be more violet than UV. (Do you see light when you run current through it?) A true UV (415nm) LED from DigiKey costs $10, so I suspect the RS version has a longer wavelength.

    You could try using two of those LEDs and putting a UV-blocking filter (i.e. sunglass lens) in front of one of them. You will also need to come up with a way to calibrate the difference between them to come up with the UV component.

    -Phil
  • Spiral_72Spiral_72 Posts: 791
    edited 2011-02-08 09:46
    Me thinks Orion Telescopes and binoculars has such a filter.


    Also, I'm too lazy to look it up, but black polycarbonate may work as well.
  • homosapienhomosapien Posts: 147
    edited 2011-02-08 09:49
    In my experience, I have found that many sources of ambient light have a UV component. It may be tough to filter the UV you want vs. the UV you don't want. This is one of the reasons that IR controllers use a modulated IR source/modulated IR detector.

    -h
  • kf4ixmkf4ixm Posts: 529
    edited 2011-02-08 10:20
    yes they do emit a pretty good amount of visible light, the specs call out for 395 to 410nm with 280 mcd intensity. i may explore that idea further with the two leds and comparing the outputs. thanks to all for the suggestions!
  • bee_manbee_man Posts: 109
    edited 2011-02-08 12:22
    How about tearing apart an old Eprom, they have a quartz window that allows UV to pass thru. I don't know how much it will block out your unwanted wavelengths.
  • LeonLeon Posts: 7,620
    edited 2011-02-08 12:27
    Quartz is also transparent to visible light.
  • SteveLSteveL Posts: 6
    edited 2011-02-08 12:33
    Apply sunscreen to your incandescent bulbs. They do have UV in their output spectra.

    Seriously..... There are materials that will transmit UV wavelengths and block all others. Edmund Optics was already mentioned as a source for such filters. Newport Corporation is another. The problem is that these filters is they can be quite expensive. $50 or more for a 1" dia. filter is probably more than you want to pay for this project.

    One possibility for a cheap solution, try a theatrical lighting suppply company. The gel filters used in stage lighting may give the solution you need. These gels come in sheets that sell for a few dollars and you can cut out the size you need. One company that makes these filters is Rosco, and they have spectra plots for all of their color filters available online. Sheets of different colors can be stacked to create bandpass filters. It will take at least 2 different sheets to get the bandpass you desire. The problem with this solution is that you may not be able to get the UV transmission you need. Most of their filters roll off steeply below 400nm.

    Another alternative would be to shield the sensor from stray. A dark tube slipped over the LED will accomplish this. The sensor would then only respond to whatever it is pointed toward.
  • localrogerlocalroger Posts: 3,452
    edited 2011-02-08 16:07
    With regard to gel filters often a simple request will get you a free sample booklet with a small say 1 by 2 inch sample of every filter they sell.
  • ElectricAyeElectricAye Posts: 4,561
    edited 2011-02-08 16:42
    You can find the spectra of the Rosco filters on this page. There are little boxes next to each color that will open up to the curves.

    http://www.rosco.com/us/filters/roscolux.cfm#colors
  • kf4ixmkf4ixm Posts: 529
    edited 2011-02-08 16:43
    thats a great idea about the gel filters, i hadn't thought about those. i will definantly check into that!
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2011-02-08 17:07
    Back to the differential reading idea: clear polycarbonate (e.g. LexanTM) blocks UV. You could put that over one of the LEDs for a comparative reading.

    -Phil
  • kf4ixmkf4ixm Posts: 529
    edited 2011-02-09 07:51
    Thanks for the info on the lexan, i was thinking it did block uv. i have comparator, dual channel ADC and a couple of uv leds im gonna start breadboarding. i have a few various lenses that i scrapped out of some old cameras to try to expand the 30o fov to ideally 90o, but 60o will work. and hopefully the lenses i have dont have any uv blocking coating, testing will determine this. i would think the first lens in a camera (outer) would have the uv blocking coating and any others inside would not, we will see!
    Phil Pilgrim (PhiPi) wrote: »
    Back to the differential reading idea: clear polycarbonate (e.g. LexanTM) blocks UV. You could put that over one of the LEDs for a comparative reading.

    -Phil
  • wjsteelewjsteele Posts: 697
    edited 2011-02-09 13:47
    kf4ixm wrote: »
    well, from what i've tested with (radio shack uv led's), the uv led's seem to be somewhat sensitive to ambient light (indoors incandesant).

    That's because incandesant lights actually emit in the UV band as well as visible and IR. You won't fix it by putting a filter in front of it because of that fact.

    You'll need to look at filtering the data instead.

    Bill
  • HumanoidoHumanoido Posts: 5,770
    edited 2011-02-10 04:51
    If you're trying to filter out specific wavelength components of UV, you'll need to pay the money for the filter. Try the companies that supply filters for astronomical telescopes. A line of UV filters is common for various spectral research programs. UV is used to study and enhance cloud formations on planets like Venus and Mars. Tri-color imaging often uses the UV component for image reconstruction. If your purpose is only to filter LED light, you won't need optical quality and can probably pick up a "seconds" with some blemishes, really inexpensively, yet it will still work for your purpose.
  • kf4ixmkf4ixm Posts: 529
    edited 2011-02-10 05:00
    basically what im trying to do is make a home-made uv sensor, using local observations from noaa to calibrate it to a measurable reading to scale from 1-16. the sensor would be part of a weather station or solar water heating system to measure efficiency of solar panels. they do sell uv index sensors around the range of $85 each, but whats the fun of that? :)

    (To Moderators, seeing how this thread has somewhat transformed into a sensor related topic, feel free to move if you think it should be.)
  • james garnerjames garner Posts: 1
    edited 2012-02-10 09:30
    kf4ixm wrote: »
    Good morning all, does anyone know of a material that will let UV (a, b or c) only light/radiation to pass through? after a few google searches, all i can find metioned is lenses for cameras, which are very expensive. im just looking for something to put in front of a uv led and use the led in reverse-bias mode as a home-brew uv sensor. any help is greatly appreciated!




    I may have and answer to your problem. I am working on a project now that requires only UV radiation be detected. Get back to me. Very simple and no added expense.


    Thanks

    James Garner
  • David BDavid B Posts: 592
    edited 2012-02-10 12:51
    Maybe you could use a reflective diffaction grating and put your sensor at the UV end of the reflected output.
  • Mark_TMark_T Posts: 1,981
    edited 2012-02-10 12:57
    kf4ixm wrote: »
    basically what im trying to do is make a home-made uv sensor, using local observations from noaa to calibrate it to a measurable reading to scale from 1-16. the sensor would be part of a weather station or solar water heating system to measure efficiency of solar panels. they do sell uv index sensors around the range of $85 each, but whats the fun of that? :)

    (To Moderators, seeing how this thread has somewhat transformed into a sensor related topic, feel free to move if you think it should be.)

    You presumably want a detector that doesn't degrade in constant sunlight for years? That could be an issue in itself.
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