Hi I have seen the N&W rulebooks with the double head masts shown having some aspects with lunar showing on the top head. Since most searchlight heads can only show three colours it puzzles me a little as to how the N&W lunar masts worked. Did they have 4-colour head at the top? Did they have a restricted set of aspects? It is hard to imagine that they would have done away with Clear, Stop or Approach aspects just so they could show the lunar aspects. Suzie x
I am not familiar with N&W signal rules, but perhaps the signals you describe were used in complex terminals or interlockings where a clear signal was impractical. For example, some of the signals that used to be installed at Tower 55 in Fort Worth, Texas were setup to display only stop, lunar or approach aspects. These particular signals were all within the interlocking as you'd navigate through crossovers or diamonds and many were within tens or hundreds of feet of each other, so it wasn't realistic to act on a clear signal even if you got one. Of course those signals are all gone now and replaced with new Type D signals throughout the plant. And you actually can and regularly do get clear signals through the Tower now.
Lunar aspects are just simply the color of the moon, and around here are restricting signals (restricted speed)
It's like the color of the moon, kinda that Whitish-Greyish. They can be used as authority into non-signaled other than main trackage. Here is a Lunar signal aspect;
On N&W the Lunar White is used differently to how it is used on most of the others or where it typically means Restricting. It only appears on three aspects and is always the top head on a double head mast:- Lunar over Green = Diverging Clear Lunar over Yellow = Diverging Approach Lunar over Flashing Yellow = Diverging Approach Diverging I guess it could be used somewhere that you will only ever take the divergence like the end of a loop, with red and lunar available on the top head, and red, yellow and green available on the bottom head, but it seems a bit excessive to have a whole load of special aspects just for that case when a triple head mast could be used without having to use lunar. If the heads could show four colours then it makes sense. I guess that someone must have a picture of one of these masts that might help explain why it is there!
Four aspects (red, yellow, green and lunar/white) can be generated with only three light sources: red, green and blue. Red + green will appear yellow and red + green + blue will appear lunar/white.
That is how it is done with a model head (the Signalist heads and decoder work this way), but I am not so sure that the prototype did it this way.
My understanding was the prototype has a single, white, bulb and a set of two or three filters / lenses and a motor that moves the correct aspect filter in front of the bulb. Then the manufacturers say 2 lenses costs $much and 3 lenses costs $much_more, and we'll let you pick the colours for free. You could achieve the same thing with three bulbs; but I hadn't heard of a four-aspect in one searchlight design ?
