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LEDs that are visible in sunlight

Discussion in 'General Electronics' started by Jason Hsu, May 1, 2004.

  1. Jason Hsu

    Jason Hsu Guest

    What LEDs do you use for a display that needs to be readable in
    sunlight?Obviously, regular LEDs are too dim. From what I have heard,
    the LEDs should be at least 2000 mcds in brightness, have at least a
    60-degree viewing
    angle, and have clear or diffused lenses.

    But for all the sources of LEDs, the >=2000 mcd LEDs have viewing
    angles that are no larger than about 20 degrees. I realize that
    there will be some trade-off due to energy issues (analogous to
    highly directional antennas vs. omnidirectional antennas), but I'd
    like to hear your real world experiences.

    What do you suggest? Should I trade off viewing angle to get the 2000
    mcds? Should I trade off the mcds to get the 60 degree viewing angle?
    Do I simply need to look harder and be prepared to pay more?

    Jason Hsu, AG4DG
    http://www.jasonhsu.com/ee.html
    http://groups.yahoo.com/group/eeham/
    http://groups.yahoo.com/group/resume_hyperinflation_fighters/
    http://groups.yahoo.com/group/gmu-ece-control/
     
  2. Tim Wescott

    Tim Wescott Guest

    Perhaps you should think about using an LCD? More involved to drive,
    but certainly visible in sunlight!
     
  3. What LEDs do you use for a display that needs to be readable in
    Uhhh...

    Take a walk through the strip in Las Vegas some time, count the LED
    billboards. Count the plasma billboards. Count the LCD billboards.
    You'll be able to count LCDs on the fingers of one elbow.
     
  4. John Walton

    John Walton Guest

    Luxeon emitters -- quite expensive, big and brite

    Agilent has a whole series of ultra-brights on their website.

    Note -- an LED's brightness is inversely related to temperature --
     
  5. Ken Scharf

    Ken Scharf Guest

    There certainly are led's bright enough to see in daylight. Many of the
    new traffic signals actually use leds! Not to mention the brake lights
    on many trucks. But these are clusters of smaller leds packed into a
    tight bundle and housed in reflector.
     
  6. Jason Hsu

    Jason Hsu Guest

    The application is an SWR/wattmeter for amateur radio. An LCD would
    not be suitable because the power level fluctuates many times per
    second during voice transmissions (AM or SSB modes). This would
    render the numeric readout useless. True, there are ways to smooth
    out the fluctuations, but that would make the SWR/wattmeter less
    responsive. On the other hand, an LED display in dot mode would
    simply appear to be in bar graph mode during these voice
    transmissions.

    Jason Hsu, AG4DG
    http://www.jasonhsu.com/ee.html
    http://groups.yahoo.com/group/eeham/
    http://groups.yahoo.com/group/resume_hyperinflation_fighters/
    http://groups.yahoo.com/group/gmu-ece-control/
     
  7. Dave VanHorn

    Dave VanHorn Guest

    It's not such a worry. I have SMD leds from chicago miniature, in a product
    with light pipes, that are quite visible outdoors in full sun.
    www.mobilecommand.net
     
  8. JeffM

    JeffM Guest

    Should I trade off viewing angle to get the 2000 mcds?
    As Tim said, do think about a different (reflective) technology.
    If you're stuck on LEDs, recess them into a black substrate.
     
  9. Irish LaidE

    Irish LaidE Guest

    try luminex.com
     
  10. Jason Hsu

    Jason Hsu Guest

  11. Tim Wescott

    Tim Wescott Guest

    Take a walk through the electronics department of your local store.
    Count the LED calculators. Count the plasma calculators. Count the LCD
    calculators.

    Maybe I'm wrong but I thought the OP was talking about handheld, battery
    powered equipment.

    If he's building stoplights, yes LED's are the right choice.
     
  12. 30 degree ~5,000 mcd (at 20 mA) and 45 degree 2,000-3,000 mcd (at 20 mA)
    are now available in orangish red, reddish orange, green and white.

    60 degrees is less common for high brightness LEDs and usually made with a
    diffused package, but should be able to exceed 1,000 mcd.

    There are rectangular flat-tip packages with a nominal viewing angle of
    100-120 degrees and those get around 500 mcd, maybe somewhat more
    nowadays (at least for green and white).

    - Don Klipstein ()
     
  13. Dave VanHorn

    Dave VanHorn Guest

    CMDA5-1 is the part number.
    The MCD rating is not spectacular, but they are surprisingly bright, and
    quite visible in full summer sun.
     
  14. G.Beat

    G.Beat Guest

  15. What LEDs do you use for a display that needs to be readable in
    Yes... but actually that's not where your thinking and mine diverged.
    I'm not sure why, but I was thinking of transmissive LCDs (i.e.
    backlit color TFTs and STNs), which by and large are totally
    unreadable in sunlight.
     
  16. Tim Wescott

    Tim Wescott Guest

    I have a radio from Tandy Aerospace in my truck. It's an otherwise
    cheap piece of crap (the radio, the radio), but it _does_ have an
    always-on LCD clock that's reflective when the truck's off and backlit
    when the truck's on. Very nice. Doesn't make up for the sound when
    it's turned on, though...
     
  17. Tim

    Tim Guest

    OK, I built a small 4 digit score board for use outside, and I used LEDS
    I salvaged from clusters I bought on E-Bay. The clusters were red/green
    mix, and the red ones really are bright in sunlight. Oddly enough the
    guy e-mailed me recently to say he had more of 'em for sale.

    Here's the web addy he gave me;

    http://www.evaluecomp.com
    (The clusters are on page 5 of the LED list)

    It takes a fair amount of effort to get the leds out of the clusters. I
    just cut the case off, and used a blow torch and heated the base until
    the solder got hot enough to pull the pcb off the back, then I just
    broke apart the expoxy or glue or whatever and retrieved the leds. I had
    about 93% success rate, with the other 7% damaged or failed after they
    were removed.

    Works nice, even at the beach, but the green ones can be hard to see
    sometimes.

    - Tim -
     
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