> >> I wonder how visible a 20ma white led will be.

> > Say around 300 - 350 lux.
> > About as bright as a typical LCD monitor.

> > You will have no problem finding LEDs with less than half that efficiency :-(.

> Real Red, Green and Blue are probably better as the White LED doesn't
> really exist. You have conversion loss of the phosphors from violet or
> near UV?

I answered for white as that was the question.
However, the best white LEDs are so efficient that they may still be
worth filtering down to a desired colour.
This doesn't HAVE to be the case, but white seems to be doing very
well indeed at the top end.
You can get White LEDs with 160 l/W (lumen/Watt) at 30 mA and 130 l/W
at 50 mA (NSPWR70CS-K1 - I use them) and eg the Osram Golden Dragon
Plus Super White is rated at 140+ l/W at 100 mA. As the OGDPSW is
rated at far above that current level, that would be a VERY expensive
solution, bnut it shows where things are going. People can make ultra
high efficiency LEDs in colours but they are raer than you'd expect.

As lumens are related to eye responsiveness the l/W rating varies with
colour for constant mW_light/ mW_DC.  Thus deep blue LEDs are often
quoted in mW output rather than lumen. However, the red LED in that
triple is red at 46 l/W and the green and blue are lower and much
lower.

 > Given the size you don't need expensive RGB LED, but just clusters. Also
> since the colours & LEDs are not equal, some colours might be two LEDs
> in series.

Yes. But that Jesse's  Osram part is in fact extremely good value for
money. 80c in 3000 quantity with 3 x 1 Watt capability =~ 30 cents per
Watt. That's extremely good for a quality part. I'd be very happy to
pay that little per Watt - apart from the low efficiency which is
unacceptable in my application.



               Russell
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