Can anyone explain how the SP Single Color Light signals are used? If you have only one lamp, how do you show red/orange/green? Did they always come with one lamp above a second? - and if so, were two colors used together to mark a particular state of the road?
Any help welcome on this!
A searchlight signal uses a single permanently illuminated light bulb.The colors are changed by a relay that is used to position a colored spectacle in front of the bulb which give different signal aspects.Sorry not sure about the answer to your other question.ops:
This site should help you as well. http://en.wikipedia.org/wiki/Railway_signal#Color-light_signals
Hi taffy. http://www.the-gauge.com/showthread.php?t=14846
contains copies of Canadian signal indications.
What you'll see is that having more heads allows for more variety or subtlety in the signal indications. Most of the indications are for junctions giving speed restrictions through the interlocking followed by a different (or same) speed on the plain track following. Canadian signalling does not normally give route information.
The other 2-head signals are home and distant (top and bottom head respectively) giving the status of the next 2 blocks ahead. These are the ones where the heads are on opposite sides of the post. Disclaimer: these signals are Canadian and out-of-date. American railroads have their own ideas -- different indications for the same feature -- and some use quite different applications.
If you trace the different indications, you'll find that they are designed so that a burnt out bulb gives a more restrictive indication if you assume it is red. The railroad rule is always that a dead bulb must be treated as the most restrictive of the possibilities.
ops: