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

[David Johnson <trainman@ozemail.com.au>]

arthur marsh wrote:

> 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.

Yes, but the railway signals have to be a set standard colour.  Green and Yellow LEDs
are too easy to mistake without a filter to modify the colour to within the standard.

--
David Johnson
CityRail Guard
trainman@ozemail.com.au
http://www.ozemail.com.au/~trainman/