What filter for White LED's

Discussion in 'Digital Cameras' started by Steve Wolfe, Jan 15, 2006.

  1. Steve Wolfe

    Steve Wolfe Guest

    What type of color correction filter do I need to remove the excessive
    It would depend on the LED in question. If you can't see it, it's even
    possible that the camera is picking up a little bit of near-UV.

    steve
     
    Steve Wolfe, Jan 15, 2006
    #1
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  2. Steve Wolfe

    Prometheus Guest

    You could try a UV block filter; white LEDs are UV LEDs with a
    fluorescent material, the one I just looked at appears to have violet,
    green, yellow & red emissions with very little blue (My home-made
    spectroscope is none-too sharp however). The UV component of the LED
    should be filtered out, but some of the specifications I have seen do
    have some residual. Don't forget that digital cameras do have some UV
    sensitivity, I have taken a few experimental shots with one UV LED to
    confirm that it is possible.
    I was thinking about this but with UV or perhaps IR LEDs.
    Sounds like there could be some fluoresce in the material, if so then a
    UV block on the lens will not help; for this you would need to either
    put a filter over the LEDs (it would not need to be very good optical
    quality, or research LEDs to find a type with less UV leakage.
     
    Prometheus, Jan 15, 2006
    #2
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  3. Does your camera have a custom White-Balance facility ? Have you tried it ?
     
    Malcolm Stewart, Jan 15, 2006
    #3
  4. Steve Wolfe

    Alan Guest

    It would depend on the LED in question. If you can't see it, it's even
    possible that the camera is picking up a little bit of near-UV.
    [/QUOTE]

    If the camera has a manual white balance compensation then this may be a
    way of adjusting for the colour shift.

    <http://www.dpreview.com/learn/?/key=white balance>

    A quick experiment with my camera and a white light LED torch and I can
    get white to blue by just adjusting the preset 'white balance'
    compensation options on my camera.
     
    Alan, Jan 15, 2006
    #4
  5. Steve Wolfe

    DHB Guest

    If you camera allows you to set a custom White Balance (WB)
    that's likely the best solution. A "white" LED is actually a blue LED
    illuminating a yellow phosphorescent material, the result is what we
    see as "white" light.

    The human eye/brain is constantly adjusting what we perceive
    as white & in most case it does so remarkably well. When we walk in
    for outdoor sunlight or the reverse our eye/brain adjusts which is why
    indoor "incandescent" (tungsten) lamps don't appear yellow to us or
    the outside light "blue" when we go back outside.

    A digital camera is not as good at "auto" WB which is why many
    models offer both several "preset" & a "custom" WB that you can set in
    addition to "AUTO WB". Getting back to your homemade macro ring
    light, you have only 2 options as I set it.

    1> If your camera has a custom WB, use it to set the exact WB
    needed to make your LED light "white".

    2> Filter the "light source only", in this case your LED ring
    light. A slight yellow filter over the "LEDs only" might work well
    but it will absorb some of the light, so you may need longer exposures
    to achieve the same results.

    2 last notes: 1> With some LEDs, the color temperature may
    shift slightly if they are driven to or just over their maximum
    ratings. So it might help to lower how hard your driving the LED ring
    light & see it that helps correct the problem. 2> Not all LEDs are
    created equal, so depending on the manufacturer & type, your results
    may be different.

    Hope this information proves helpful to you & or others.

    Respectfully, DHB




    Good luck
    "To announce that there must be no criticism of the President,
    or that we are to stand by the President, right or wrong,
    is not only unpatriotic and servile, but is morally treasonable
    to the American public."--Theodore Roosevelt, May 7, 1918
     
    DHB, Jan 16, 2006
    #5
  6. Steve Wolfe

    Mark² Guest

    You don't need a filter.
    You simply need to use custom white balance settings on your camera.
    See your camera's instruction book for how to do this (since it's a little
    different with each camera).
    You'll have to do it for each shoot, though, since your lighting is nearly
    always going to be a mixture of LEDs and ambient lighting...which means you
    need custom-tailored WB for each.
    It's really very easy with most cameras.
    -Mark
     
    Mark², Jan 16, 2006
    #6
  7. Steve Wolfe

    Steve Wolfe Guest

    I built a ringlight for macro use with my Olympus C-770 digital camera,
    If he wants to buy new LEDs, there are some that have red, green, and blue
    LEDs packaged in the same unit - which would allow him to adjust the color
    of the LEDs to what he wants. I've always thought that would be a fun
    project for a macro ring-light, but since I don't do macro shots, I've never
    tried it. : )

    steve
     
    Steve Wolfe, Jan 16, 2006
    #7
  8. Steve Wolfe

    Jim Guest

    What type of color correction filter do I need to remove the excessive blue
    from white LED's. White LED's are pure white to the eye, but my camera sees
    blue also.

    I built a ringlight for macro use with my Olympus C-770 digital camera,
    consisting of 24 white LED's, 20,000mcd each.

    It works well, except for one hitch: the light the camera sees is blue.
    Not a light blue caste but a medium blue when reflected from white paper or
    cloth. My ringlight has 52mm threads, so I can use a 52mm filter between
    the camera and ringlight, but I do not know which one to use.

    I tried some of the yellow B&W filters I have, and they do reduce the blue,
    but now everything is yellow. I know little about CC filters so need help
    in selecting the right one.

    Thanks
    Jim
     
    Jim, Jan 16, 2006
    #8
  9. Steve Wolfe

    Jim Guest

    I did try a Tiffen HAZE-2A with little or no effect, but I don't own any
    other (yellow) UV filters to try.

    I have built several light rings using IR LED's but have only tried them
    around the house so far. I have an IR pass filter, so thought they may be
    interesting to try in flower photography. If you try to build one, design a
    board to use LOTS of IR LED's.....mine are high power 875nm types (HP).

    Jim
     
    Jim, Jan 16, 2006
    #9
  10. Steve Wolfe

    SteveB Guest

    The 770 can do the manual WB necessary to calm down the blue cast, but it
    may still be better to get the LED light nearer to white so that there
    aren't such major mixed lighting problems. I've done this with excellent
    results using yellow(ish) filters over too-blue flashes on cameras without
    manual WB, making my own filters out of clear inkjet labels with the right
    colour printed on them to balance out the caste. How the right colour is
    arrived at could just be by trial and error, or by taking a photo of a LED
    lit white surface, use the dropper tool in PS or PSP etc to measure the RGB
    balance of the resultant bluish caste, and print a label with somewhat
    opposing values. E.g. if the dropper says 200 200 240, then print a label
    240 240 200 for starters, then try it again with the label over the LEDs and
    see how much closer it is & fine tune from there. Cover the printed surface
    with a second clear label for protection.
     
    SteveB, Jan 16, 2006
    #10
  11. These integrated RGB leds may give some funny shadows, as there still are
    some distance between the three differently colored emitters.
    I have tried separate RGB (Luxeon Stars - about 20mm distance between
    emitters), and they gave very distinct shadows.
    Please try it anyway and report here.
     
    Frode P. Bergsager, Jan 16, 2006
    #11
  12. Steve Wolfe

    Steve Wolfe Guest

    These integrated RGB leds may give some funny shadows, as there still are
    Like I said, since I don't do macro, it's never been more than a passing
    interest. A quick search of Digikey's catalog shows some surface-mount RGB
    LEDs that are as small as 2.8x3.2mm, and larger units up to 5mm in diameter.
    I would imagine that those would produce much better results, and if not
    entirely acceptable, a small diffuser would surely make a big difference.
    They're not terribly cheap, however.

    The catalog is available at http://dkc3.digikey.com/PDF/T061/SectO.pdf ,
    and the models are at the bottom of page 1737.

    steve
     
    Steve Wolfe, Jan 16, 2006
    #12
  13. Steve Wolfe

    Jim Guest

    Thanks for approaching my question this way. All the suggestions about
    depending on the white balance are fine, but I often take 100 to 150 photos
    per day during the spring, and the white balance really needs to be re-set
    for each photo using this method. Using the corect filter to balance out
    some of that blue would certainly make life easier.

    FYI for anyone using this post as an information source, trying to duplicate
    what my question suggests..........I got a y44 (light yellow) filter and put
    it in front of the LED's so the light is filtered, as well as the image
    going to the lense, and it is surprising how well this works, at least
    indoors. Maybe not the BEST balancing solution, but pretty good.

    ALSO, FYI, the mention of shadows........I use 24 LED's 20,000mcd each, in a
    ring, mounted INSIDE a 52mm filter ring so I can still use the threads. The
    LED's firstly, are the frosted type, and are close enough to the image line
    that there are no shadows. I also have a 52mm diffuser that I machined a
    hole through that I can use (don't know if it changed the light temp.
    though).

    The problem with this exact setup is obvious........at wide angle
    setting.....which I usually use for macro........the LED's are in the photo,
    so I have to back off some to get them out of the photos....I'm building one
    in a 67mm filter ring with a larger center hole!!

    Jim
     
    Jim, Jan 19, 2006
    #13
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