I often see posts asking about resistor values, so here is an attempt to provide some data for various supply voltages....

http://cabin-layout.blogspot.com/2017/04/led-lighting-circuits.html

Its always seemed odd that they are called Light Emitting Diodes, when they really are better named Light Emitting Semiconductors. Because LEDs in general suck at being usable diodes due to their very low failure voltage (Vr) as opposed to a specified break-down (non fatal) voltage (Vbr) (ie you need a diode to protect the diode), and they have a higher forward voltage drop than simple silicon diodes that only have 0.7v forward voltage drops.

They really are semiconductor lights, as they have been designed for their light emitting characteristics and not for diode behavior.

since I've been converting loco to digital I've been using Led's, first I started of with 1,8mm tower and 3mm round and some 5mm for the Santa Fe diesel loco's headlights but things have improved since than and I use mainly smd leds with various sizes, from 604 to 1200 and the same goes for resistors, they take up much less room.
I've converted many carriages with led lights and some of them amount to 10-12 carriages, all having about 12 led's within. these are divided into 4 groups (3 led's each) and all my carriage lights are powered by the loco decoder via electrical couplings.

instead of buying expensive interior lights I make them myself, for open car carriages I use led strips and for compartment coarches I make them up myself, configure them in such a way that toilet, gangway and individual compartment are all lit in the right place, it also gives me the choice of leaving some compartment without light, like the prototype.

having an enormous amount of passenger carriages it would have cost me an arm and a leg and by doing it yourself helped me keeping the costs down.
for instance I've just working on a SBB Re 460 with Swiss light change and added red marker lights either single or double.

regards.,

John

thanks guys. this is an interesting subject in which I will be getting stuck into during the coming winter. Very helpful

I will be working on analogue engines/loco's and my problem I will be dealing with is how to switch the circuit for the change of direction of head lights, without having to make up a mickey mouse reversing switch. If anyone knows of a micro switch that will work in ac, i would appreciate the help in locating something.

Dereck