Andy Wrote
> I need to generate Red, Amber-ish, and Green from a single LED body (standard
> T1.75 size).
>
> I am limited to a common-cathode device with two anodes to select the desired
> color.
>
> The P391 from Digi-Key doesn't blend the colors well when both LEDs are turned
> on, it's obviously a red and a green LED in the same package.
>
> Anybody have any experience with LEDs that _will_ work well?  Vendors?
>

We do a lot of LED colour mixing and the ONLY way we can get
uniform colours and target spots to to have separate leds with a
narrow beam aimed at a white/neutral translucent target.
As others have said... the multichip leads dont target well.

BTW for wide range colour generation we use bright Red Green and
Blue LEDS each matched in intensity (or at least compensated for)
driven each by voltage to current sources, fed by 3 D/A converters.
The target is a hole in a metal sheet covered with white translucent
plastic. The beams are positioned so each shines from behind on
an area slightly larger than the hole. The result is a wide range of
digital selectable colours.
Works very well.
_____________________________

Lance Allen
Technical Officer
Uni of Auckland
Psych Dept
New Zealand

www.psych.auckland.ac.nz

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