Re: A few things a'changing....

[arthur marsh <marsh@ties.itu.int>]

LED's have a moderate emission range - and so can appear green, yellow /
amber and red without any coloured plastic housing. One typical packaging
of LED's is to have green emitting and red emitting semiconductor side by
side on the one LED, so that DC current in one direction will produce red
light, DC current in the other direction will produce green light, and AC
current will produce an amber light. A collection of such LED's could make
a quite effective 3 colour railway signal lamp.

The common LED encapsulation in a block of plastic in the shape
of a hemisphere on the end of a cylinder provides a reasonably
directional spot of light.

Arthur.

On Sat, 6 Feb 1999, David Johnson wrote:

> > : At Yarraville - signals with LED's rather than traditional globes.
> > : These are sensational - their visiblity is FAR, FAR better than old
> > : colour light jobs.  It's lots and lots of LED's together forming one
> > : intensely bright signal.  I wonder if a tri-colour LED setup in a single
> > : 'light' could be used to produce the three colours?  At this stage, they
> > : retain 3 individual 'lights'.
> 
> No.  The LED signals have a colour filter to make the signal look correct.  If
> you had all the LEDs in one lens, there would be no way of filtering them to the
> right colour.
> 
> --
> David Johnson
> CityRail Guard
> trainman@ozemail.com.au
> http://www.ozemail.com.au/~trainman/
> 
> 
> 
> 
>