Question about RGB LED.

Discussion in 'General Electronics Chat' started by kurtruk, Jul 18, 2013.

  1. kurtruk

    Thread Starter Member

    Aug 26, 2012
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    Hello, I have several RGB 5MM LED that I have been playing around with an Arduino by using PWM. When I try to mix colors, the result appears to be three separate LED's right next to each-other, rather then one fluid color. My LED's are water clear, rather then diffused could this be why? Or is it something else?

    I am using simple 5V power supply from the Arduino and I am using 360 Ohm resistors for each color.
     
  2. crutschow

    Expert

    Mar 14, 2008
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    To see the mixed color you have to be far enough away from the LEDs so that you can't resolve the individual LED colors. A diffuse LED would help or a diffuse screen in front of the LED, such as wax paper.
     
  3. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Are they pulsed R then B then G? May be you're not pulsing them fast enough for persistence of vision to take over.

    If you turn them all on do you see R, G, and B or do they mix?
     
  4. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    The low-cost 5mm RGB LEDs are not really meant to mix colors. The intensities are not well matched at equal currents.

    You will have to play with the values of current limiting resistors and the. Pulse differently to get the color mixing you want.

    Use ScotchBrite pad or 1000 grit sand paper to diffuse the LED. Otherwise, use a white glass diffuser. Make sure it is white because even slightly yellow diffusers will screw up your pallet.

    Make sure you are pulsing each color at least 60 times per second. 100 Hz is even better (each color).

    In general, you only need 2 lights on at one time. Adding a third color just makes the blended color more pastel or closer to white.
     
  5. atferrari

    AAC Fanatic!

    Jan 6, 2004
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    How good could it be if I try that with say, 40 LEDs?


    Is it a specific thing? Expensive?

    I know that a variety of papers could work as difusers but for a masive number of LEDs seems not practical. Tried with few in fact.
     
  6. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    The light output angle of the LED is usually less than 20 degrees for the round 5mm models. The small distance between the LEDs is maintained and an array of bulbs just causes the offset to be projected across your diffuser.

    The glass diffuser is just from a table lamp or ceiling light fixture. The one from below was purchased at ikea.


    If you are going to wire up 40 RGBs, just get one or two LEDs that have 1 Watt per color. The best part of that is, high wattage LEDs are available in wide-angle (140 degrees and more). That way, the non-overlap of colors is very small ratio vs. overlapped.

    The lamp in the photo uses one LED. 350 mA per color. Blending is beautiful. Colors drift and blend based on Pwm - only two colors are one at a time. Intensity is equalized (one lamp color reducing while the other increases. It takes about 15-20 minutes to work through the color wheel.
     
    Last edited: Jul 19, 2013
  7. atferrari

    AAC Fanatic!

    Jan 6, 2004
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    I was thinking in fact, to assemble a small panel with actually 40 LEDs. I do not like much those panels / cubes where the LEDs are so bright that watching them is hardly pleasing (pleasant?) at all thus my interest in getting a similar even difusion on all of them.

    I lack experience with LEDs. My question: a difuser is always expected to attenuate the light, right? Any way or trick to minimize that effect, if at all possible?
     
  8. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Almost everything white will cause internal reflectance and send some light back towards the source. If it does not, it is not really diffusing.

    One interesting material is Ulexite, a natural crystal of calcium borate that forms columns of crystalites in a clear material. It doesn't really diffuse the light, it more or less columnates (makes into a column) the light hitting the stone material. It is a natural fiber optic. See the effect in the image below. See Wikipedia for moew info.

    Large crystals are expensive but my story is just an example to give you a better feel for the challenges of diffusion.
    [​IMG]

    The light cannot be directly behind the ulexite but has to be angled, as in US patent 6833951
    http://www.google.com/patents/US6833951


    NOTE:
    Interestingly, the 'shutter' speed on the camera that took the photo of yhe lamp above was fast enough to only catch only the green of the blue-green color that was seen by my eye when I took the photo. PWM frequency is about 72Hz on the lamp above.
     
    Last edited: Jul 19, 2013
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