That's a feature of the 30 volt bulbs, to be used 20 in series, often in PCC cars. Usually, the sockets in the car also have a spring contact to maintain the circuit when a bulb is removed. Of course, the remaining bulbs now burn brighter and burn out more and more quickly until there is a cascading failure of many bulbs or the fuse blows.
The shorting in the bulb is prevented by some lead between contacts connected to the filament supports. The heat of an arc melts the lead so the contacts can touch and cause the short circuit, shunting or bypassing the arc.
It's much easier to form an arc with Direct Current than with Alternating Current, and in gas than in a vacuum. However, better light can be obtained in a gas, so the gas filled shorting bulb was developed. 5 in series would be too much for the other 4 bulbs when one shorted, so they were made to be used 20 in series.
Possibly an Arc Resist bulb with no restriction on orientation has filament supports that spring away from each other if something goes wrong, like bulbs for use in explosive atmospheres. Street Railway bulbs over 100 Watts are often marked "Arc Resist", since they should be gas filled.
More knowledge and information is needed, as proper bulbs are getting rare. The German factory that was making the shorting bulbs for Aamsco refuses to make more, out of fear that incandescent bulbs may be illegal according to European ecology laws.

120V bulbs, used in a string of 5, do not have the shorting feature. If one goes out, all five go dark. They just send you hunting for the bad bulb; quite likely you can spot the bad one by visual observation, if not you have to attempt 5 swaps.

30-32V bulbs, used in a string of 20, have the shorting feature. If one goes out, 19 burn brighter.

Now, about making bulbs... http://hackerati.com/post/53425358/fabr ... mpe-triode

The Western-Electric Co. 1916 catalog has 6 diff bulb 105V, 110V,115V,120V,125V, 125V And 130V all a 64 Watt.
Each blub can be use for 525V,550V,575V,600V,625V and 650V.
Each bulb is Style S-19 , Diameter is 2 3/8" .
Plain $0.28 or FROSTED $0.33 with a min order of 250 ea.
Western-Electric Co. in 1916 ERA was a big supplier of anything.

Stan

I don't know if this helps or not, but on my occasional trips on the NY Subway I've seen sticks of five bulbs lit up at track work sites. I'm not sure if this is for task lighting, to indicate that the third rail is "hot", or both.

I didn't notice the shape of the bulb, or clear or frosted characteristics, but I'm sure that the same type of shorting features would be needed here. Perhaps one of the transit authorities with 600 VDC third rail could point out a source for appropriate bulbs.

http://www.princetonimaging.com/library ... /idxB.html

look on L for lamp, on page 634-635.


Stan

This has been a great thread. We have been able to trace frosting of light bulbs as an option (for an additional cost) to about 1916. The question now is would the street railway companies have paid for this additional option? Lets put it in some perspective. This option for frosted bulbs is around 5 cents per bulb. There are on average 20 bulbs per car. Thats $1.00 extra per car. Does not sound like much. But, in 1920 the average newspaper cost 2 cents to purchase. Today the average newspaper is about 75 cents. So now we are talking the equivalent of $37.60 per car in today's value. Lets say the Connecticut Company had 1000 cars, that would put it at $37600.00 to have the added feature of frosted bulbs. This does not include the cost of replacement bulbs as the cars needed them. Would the cash strapped companies that were competing with the automobile pay the extra cash to get frosted bulbs for their fleet or would they go with the clear bulbs?

With "cash strapped companies that were competing with the automobile"... the choice should be "clear".. (Sorry, couldn't resist-)

I'm going into NYC in a few days, and will try to get a better look at the sticks of lights I mentioned earlier.

I remember that 120v. railway service lamps on the NYCTA were specially produced with left-handed threads in the days when there were bare lamps inside the passenger cars. This was to prevent theft for use around the house by passengers (and I suppose employees.) I wonder if they still are left-handed?

Chicago used similar stands for work lights, at least when I worked there in the seventies and early eighties. Ours were a board about a foot square on a short stand, the board had a socket at each corner and one in the middle. The wire leads were soldered to common cotter pins, which were slipped over the rail bases, both running rail and trolley rail, like hair pins. I remember one of the Local 9 electricians walking around in the snow slipping the leads on the trolley rail with his gloved hand; I expected his eyes to light up like light bulbs, but apparently he had been doing it for years with no ill effects.

The bulbs were the standard frosted 120V 56W Street Railway service bulbs, same as were used in the gooseneck lamps on the platform. Back in those days most of the older stations still had the lights powered off the trolley power. The gooseneck fixtures alternated between three bulbs in one but only two in the next to give the five bulbs necessary on 600V. I remember once while renewing platform decking, in prying the gooseneck up with a bar to slip a new board underneath, we must have skinned the wires and shorted them together, because the next fixture in line got really bright, but only for about a minute.

Our bulbs had standard right hand thread Mogul bases; I had little use for 56W bulbs, but the sockets worked just fine of other projects.

Perhaps if they thought that the frosted bulbs were more modern, with clear bulbs being "so 1910".

--
Will

New York City Transit Authority still uses enough of the 56 Watt, 130 Volt, A-21 size, inside frosted, non-shorting Street Railway bulbs, burned 5 in series from the 3rd rail power, often on those temporary use boards. They are currently able to hire a factory in Communist China to make some. In the past, they used 101 Watt bulbs in those boards, but used 36 and 56 Watt bulbs for station and other lighting. When U.S.A. factories stopped making them, they tried Sylvania of Mexico, then Magyar Electric of Hungary. When Magyar became part of General Electric, they were in trouble, until they found Red China.
In New York, Brooklyn-Manhattan Transit used left hand threads for publicly accessible bulbs that didn't get hand burning hot all the time, like battery powered emergency lights. The shorting bulbs will burn fuses if used on 120 Volts house current, so BMT didn't think that they were worth protecting with special threads. The Independent City Owned Rapid Transit Railroad also used left hand threads where 2 different bulbs were in the same housing. One would be left hand thread so the bulbs couldn't go in the wrong sockets. Neither company used left hand threads for every bulb. I don't think that the Interboro Rapid Transit bothered, and Brooklyn Rapid Transit used real keys to stop the bulbs from spinning freely in the special sockets, so they could be unscrewed! ("Pssst. Want to buy a BRT light bulb socket key?")

I remember seeing a "light board" with five 101-watt frosted bulbs in Boston's Green Line subway 8 or 10 years ago, illuminating a work area.