We are repairing a block signal, tall us&s type, on a mast. We're trying to figure out the brightness of the bulb that would have been originally used. My understanding is that these used quite small bulbs, on the order of ten watts, to conserve battery power. Can anyone confirm?

Hello:
The B&O Color Position Light signals used 13 1/2 volt bulbs and some RR's used 10 volt. You can substitute auto bulbs which are cheaper. The correct bulbs from the RR had a precisely focused filament in order to take advantage of the focused lenses. They also burn a lot longer than cheap bulbs, as long as two years.
What type of signal is it ?


Kevin K.

I don't actually know the model of signal. It's not a searchlight signal, as it only displays one aspect, it's fixed at yellow. It's an approach signal for an interlocking on an otherwise unsignaled NYC branch. This is for an operating railroad museum and we'd like to get the bulb brightness historically correct for railroad practice (NYC). Also, power is a serious problem because the signal is lineside in a remote location.

I seem to recall it took a bayonet type base, like an automotive brake light bulb (1156). Looking at this page that seems about right.
http://www.railroadsignals.us/signals/bulbs/index.htm
I also - vague recollection - I recall that we examined the signal shortly after it went out of service, and I THOUGHT we found a 5-watt bulb in there. That would be consistent with the data I see on the scanned pages on the above URL.

Is that plausible?

If so, we could easily replicate it with LED lighting and a very small solar panel.

Standard signal lamps are 10V 18W. Set your power source to provide 9.5V at the lamp and the brightness should be perfect.

Lessee... 18W @ 10V = 1.8A. Resistance 5.5556 W.
At 9.5 volts, amps will be 1.709. That is 16.25 watts.

I've done some research on this. Incandescent bulbs make about 15 lumens per watt. That's 243 lumens.

However an incandescent generates all colors at once, and you don't want most of them. Blocking the unwanted light colors is the job of the colored lens/filter. This reduces the actual lumens which make it through the filter. Of your 243, I'm wild guessing less than 120 lumens of yellow would make it through, and about 60 lumens of red.

LED's are about 90 lumens a watt, except LEDs give you exactly the color you want. If the color matches the lens-filter, it'll pass through with little or no loss. 1.33 watts of LED buys you 120 lumens. Aw heck, call it 1.5 watts.

A rule of thumb on solar is to size your panel for 5x the average load. I'd favor concealment over efficiency, so I'd give lots of extra margin - 10x. That means 15 watts of solar capacity. Solar is well under $5/watt anymore. If you get individual cells on eBay, they are less than a dollar a watt, but you have to assemble them. On the other hand you can position them as you please, which favors concealment.

This could work. This could be very economical.