LED there be Light, a D.I.Y. LED ringlight

Discussion in 'Digital Photography' started by E Pericoloso Sporgersi, Aug 10, 2003.

  1. Please have a look at

    It took me hours to compose this report. So I really don't feel like
    translating it into Dutch, German and French. You'll have to read it in
    English, linguistic mistakes and all (I'm Flemish).

    Instead, I'll go play with my new photo system. <wide grin>


    1. European language (similar to Dutch)
    2. native to Flanders, part of Belgium.
    E Pericoloso Sporgersi, Aug 10, 2003
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  2. Thank you.
    Within a range of 4 to 10 cm I get a pretty unifom colour. Closer than 4 cm I
    get a central dark spot and farther than 10 cm I get a central yellow spot. To
    broaden the usefull range to 15 cm, I plan to build a ringlight with +/- 78
    LEDs, i.e. an inner ring, a middle ring and an outer ring.

    The camera's internal software compensates the white balance very nicely.
    Now that I'm getting some experience with it, that is.

    Because the ambient light affects the incident light, I have to set the white
    balance for each and every series of shots with LED light.
    E Pericoloso Sporgersi, Aug 10, 2003
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  3. E Pericoloso Sporgersi

    Mark M Guest

    Perhaps you could mount some sort of mild diffuser in front of the LEDs to
    help spread the light more evenly?
    Mark M, Aug 10, 2003
  4. E Pericoloso Sporgersi, Aug 11, 2003
  5. I don't think so.

    AFAIK Only the tag and slot idea is originally mine.
    All other design specs I gathered on the net.
    E Pericoloso Sporgersi, Aug 11, 2003
  6. E Pericoloso Sporgersi

    Browntimdc Guest

    Hi Ciskay,

    I looked at your web page for the digital camera ringlight. Looks like a
    good job and is something I hope to do one day.

    You plan to build another for higher brightness. I have a suggestion on
    how to get more brightness from your current ringlight. First, it's not
    clear how you regulate the current through the LED's. Are there series
    resistors? What is the current in each LED and are they matched? Are you
    just putting 4.5V across each LED and hoping for the best?

    If you operate the led's in a pulsed mode you can get more output. Here's
    one posibility: when the unit is turned on the LED's operate at a low,
    constant current. This would serve as a modeling light and conserve
    battery power. When the pushbutton is pressed the lights operate at high
    current for 1/2 second (555 timer IC). This is long enough to manually
    syncronize with the shutter. They should have no problem operating at 2X
    their constant rating (I've done some work testing LED's for a gloss
    meter, they are pretty robust). LED efficiency is generally higher at
    currents moderately above the continuous rating, so you likely will get
    more than one stop of light gain. I'll make a schematic if you like.

    Browntimdc, Aug 12, 2003
  7. E Pericoloso Sporgersi

    Browntimdc Guest

    I meant matched in current draw. It would be good to check the current on
    each LED. There might be considerable unit to unit variation. LEDs are
    preferably driven with constant current since there is also voltage
    variation with temperature. OTOH, leaving out the resistors is more
    energy efficient. The gloss meter work I did was 15 years ago and with
    green LEDs, so maybe things are better now.
    That would rule out pulsing at higher currents, unless the pulses were
    pretty short. The color change is probably due to chip heating. The light
    from the chip shifts to a color that does not excite the white phosphor.

    The only improvement I might suggest for the Mark 2 is a more efficient
    DC-DC convertor instead of the linear regulator.

    Browntimdc, Aug 13, 2003
  8. Gene said in a mail:
    Super performant LEDs are available, but I don't know where to find them in the

    search for leds ultrahell
    search for LED, weiß, 5mm, 10.000mcd
    E Pericoloso Sporgersi, Aug 14, 2003
  9. E Pericoloso Sporgersi

    Matt Guest

    Next problem, a reasonably priced source of white leds!

    Look what an internet search dragged up - $0.60 ($0.75 for higher

    I bet they aren't as cheap (say) in the UK - £-$ if you're lucky!
    But with shipping at $2 anywhere, any quantity.

    Is this too good to be true - are these guys for real?
    Matt, Aug 14, 2003
  10. E Pericoloso Sporgersi

    Browntimdc Guest

    I think it would be difficult to get the colors blended uniformly in a ring
    light this way.

    Browntimdc, Aug 14, 2003
  11. See for color rendition:

    Commercially available ringlights for white light all have white LEDs
    only. I haven't seen any mix of RGB.
    Amongst others there are:

    I also received this mssg:
    Francis Kennis, aka E Pericoloso Sporgersi
    E Pericoloso Sporgersi, Aug 14, 2003
  12. E Pericoloso Sporgersi

    ZZ Guest

    ZZ, Aug 14, 2003
  13. ... Or you could use a collection of red, blue and green
    Somewhat OT:

    I know it works that way (TV sets, CRT-monitors, TFT-screens and apparently LED
    videowalls too), but I'm still confused.

    I distinctly remember a (too long ago)low-level physics class in school where
    the teacher told about Newton, rainbows, prisms and the light spectrum.

    To demonstrate he had this disk divided in 24 or so (a multiple of 3 anyway)
    segments, alternately colored Red, Yellow (NOT green) and Blue.
    When he set the disk to spinning fast enough, it appeared uniformly white.

    Why is it R, G an B light instead of RYB to produce white light?
    And why does CMY together produce black?

    Please enlighten me.
    E Pericoloso Sporgersi, Aug 15, 2003
  14. http://www.4and1.de/weissabgleich.htm
    It looks like the white balance can handle the problem of white LEDs
    emitting not very much red light.

    Thanks, Michael

    -Michael Schnell, Krefeld, Germany,
    Michael Schnell, Aug 16, 2003
  15. Re RGB:

    It's not a question of physics but of how the Human eye works (it's three
    colored, while many other mammals' (e.g. horses') eyes are two-colored).

    The film material and the digital cameras (and any other video stuff) is
    designed to be a fit for the human eye.

    That is why we have the RBG color space (and all the other used for
    different purposes).


    -Michael Schnell, Krefeld, Germany,
    Michael Schnell, Aug 16, 2003
  16. The human eye uses color sensors that are (vaguely) equivalent to a set of a
    red, a green and a yellow monochromatic sensor. The digital camera uses
    color sensors that are (much more truly) equivalent to a set of a red, a
    green and a yellow monochromatic sensor.

    So if mixing colors by adding light you can produce any color from
    monochromatic red, green and blue light. But a mix from green and red
    produces the same sensation as monochromatic yellow light (RGB color space).
    "Technically" white light contains any color of the rainbow.
    "Physiologically" only three colors are enough to create light equivalent to
    real white.

    The the way the sensors in the eye are built you can also use monochromatic
    green and monochromatic yellow light to produce the sensation of white,
    though no red light is in the mix. Thus a red object (absorbing any light
    but red) will look black in this "white" light. So white LEDs look white
    though they only emit very little red.

    The RYB and CMY colorspace is for subtracting color. You can produce any
    color sensation by subtracting (filtering by a transmissive glass or a
    reflecting surface) some of the R, Y, and B parts from white light. So a
    green surface absorbs (much of ) red any yellow light parts.


    -Michael Schnell, Krefeld, Germany,
    Michael Schnell, Aug 16, 2003
  17. So that's why Stevie Wonder sings:
    "You are the Sunshine of my Life".

    Thanks Michael,
    it was already dawning on me, but now I'm fully illuminated.
    E Pericoloso Sporgersi, Aug 16, 2003
  18. It seems they're planning a kind of contest.
    Here's my entry:
    Have a look at
    To non-dentists this is patently insane.
    Just kidding of course. But this one really is ridiculous:
    (Shot taken at the reception of a dental congress, celebrating the 50th
    anniversary of the local dental association, of which I'm the secretary)
    The red thing below my chin is a bicycle's rear light (2 LEDs, battery-
    powered), set to strobe.
    The text says: "THERE're full ones ..."

    Even if you were to nominate me champion of insanity (I hope not), then just
    let me know. Please don't send me 1.000 blue LEDs. Belgian customs officials
    would probably get blue in the face and charge me taxes on the estimated value
    (and belgian customs officers are notoriously thorough in value estimates).
    Have a drink and toast my future mental health.

    E Pericoloso Sporgersi, Aug 17, 2003
  19. E Pericoloso Sporgersi

    Tim Brown Guest

    I have received an order of 25 of the 8000mcd white diodes. They are
    in a clear case so the main beam is pretty narrow. Color uniformity
    looks good. A rub on some 600 grit emory cloth would frost them
    nicely. At 20mA (3.2V) they are damn bright. Anything over 3mA and you
    can't look at them directly. I ran one up to 80mA (4.5V) for a few
    seconds and there was no obvious color shift.

    Tim Brown, Aug 19, 2003
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