🚀 go-pugleaf

In article <1990Nov5.172318.1487@phri.nyu.edu> roy@phri.nyu.edu (Roy Smith) writes:
>tom@syssoft.com (Rodentia) writes:
>> Anyone making a tricolor LED yet?
>
>fng@questor.wimsey.bc.ca (Felix Ng) replies:
>> I think Radio Shack sells one.  Red and green with DC and yellow with AC.
>
>	I think Rodentia (presumably not tom@syssoft.com's real name) meant
>an LED with all three primaries, i.e. red, blue, and green that you could
>mix anyway that you like.  The red/green/yellow LEDs are just a red and a
>green LED back-to-back.  One polarity lights one, the other polarity lights
>the other, and AC lights them both, a half-cycle each.
>
>	I could see packaging all three in one plastic case, but I don't
>see how you make it work with only 2 pins.  The minimum pin count I could
>see is 3, with the 3 LEDs delta connected, allowing you to light any one or
>two at a time.  If you wanted to light all three at once, you would need 4
>pins; an anode for each and common cathodes (or the other way around, if
>you prefer).  It would certainly be a heck of a lot simplier that getting
>the odd bipolar voltages you'd need in the delta connection.
>
>tom@syssoft.com (Rodentia) again:
>> how would power consumpion compare to LCD shutter solutions?
>
>	My latest Digi-Key catalog shows most of the LEDs drawing 70-90 mW.
>Even for a modest resolution 512 x 512 display at 70mW/pixel, you'd be
>drawing 18 kW!  Hardly low power.
 70-90mW is pretty high for an LED. Most of the ones I use draw about 20 mA 
with a forward voltage of about 2.2 V = ~45mW . But this is the instantaneous
power consumption. The brightness of an LED is a fairly sharp exponential of
the input current. So driving it with 5 times rated current and a 10% duty
cycle (should be rugged enough to stand this) will give the same subjective
brightness, but halve the power.
 Besides,the LEDS's in catalogues are discrete, butch devices for indicators.
If they were to be used in a matrix display they would be individually very
small, with concomitant reduction in power needs.
 And as for tri-colour LED's, give 'em a chance - the blue LED has only been
available for about 4 months now. It was always the holy grail of LED people,
for precisely the reason that a tri-colour LED is potentially a very useful
device...




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