Many of the higher-end LED assemblies used for stage and architectural 
lighting use this mix - they call it RBGA (amber). Some even use white, 
as well. I guess you get a better mix gamut that way and have more 
control over the color and how natural you can make the white balance. 
It's also worth noting that they tend to use 16 bit controls on the PWM 
for dimming. It seems that fewer bits than this (i.e. less temporal 
resolution in the pulses) gives you visible steps (quantization errors) 
at low light levels.

Alden

Steve Baldwin wrote:
> That will probably be so that they can be used in a traffic or automotive 
> application. You can make orange from green and red, but a failure results 
> in a red or a green where an orange should be. ie. It doesn't fail safe (see 
> earlier thread).  Traffic lights are the obvious one. It's pretty tightly regulated 
> for roadage signs as well as the colour infers the importance.
>
> Steve.
>  
>
> On 27 Nov 2006 at 11:03, Mike Hord wrote:
>
>   
>> I just bought some LEDs from Digikey/Mouser for a color mixing
>> project I'm thinking of playing around with (why paint when you
>> can light?), but I'm a little confused by the fact that the "matched"
>> LEDs I bought come in FOUR colors: RGB and orange.
>>
>> This is new to me, and you-know-whoogle doesn't have anything
>> to offer.
>>
>> I accidentally bought GBO in my first order, so I picked up some
>> red ones from Mouser (same manufacturer part number, but
>> Mouser doesn't have a minimum order)(I prefer Digikey due to
>> proximity).  I have all four- am I "supposed" to use them all?
>>
>> Mike H.
>> -- 
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>
>
> ==========================================
> Steve Baldwin                          Electronic Product Design
> TLA Microsystems Ltd             Microcontroller Specialists
> PO Box 15-680, New Lynn                http://www.tla.co.nz
> Auckland, New Zealand                     ph  +64 9 820-2221
> email: steve@tla.co.nz                      fax +64 9 820-1929
> =========================================
>
>
>   

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