1920

Two interesting testing devices are pictured above. On the left is a very inexpensive dual purpose "socket shorter." When the smooth end is inserted directly into a series wired miniature base socket, the tester effectively bypasses the socket by shorting it out. Using the device would be quite tedious, as the operator would have to remove each lamp in a string of eight lamps one by one and insert the tester to find the bad lamp. This operation would be little different from the suggestion of most outfit manufactures: take a known good lamp and exchange it in each socket on a festoon one by one until the set lights. However, the tester was advertised for an additional use: as a temporary "bad bulb replacement." By using the threaded end of the unit in this way, it would be left in place as a "substitute lamp" until a proper replacement could be had. The disadvantage of this, however, is that each lamp remaining in the string would receive a higher voltage, thusly shortening their operating life.

A slightly more practical tester is shown on the right. A pliers-type device, it was used by pinching the pair of wires under each series-wired socket. The fine teeth on the blade would penetrate the  insulation on the wires, again electrically shorting or bypassing the socket. While much faster to use than the bulb-substitution method or the other tester, the fine teeth on this unit would easily cause premature insulation fraying where the wires were gripped. Obviously, neither tester was a truly practical solution to the series-wired problem.

1920

One of the earliest attempts at solving the problem within the wiring itself was offered by The Franco Electric Company. A rare outfit, this festoon consists of ten sockets, rather than the usual eight or nine. With ten series-wired sockets, each 14 or 15 volt lamps would receive about 11 volts each when used on a typical 110 volt household power circuit of the times, dramatically increasing bulb life. The downside of this configuration is that each lamp will burn with only about 2/3 of its full brightness. 

    

1924-1925

Another interesting attempt to solve the problem within the wiring itself was offered by Triangle/Berwick in 1924. Called the Detect-O-Lite outfit, this string had an ingenious control box on the string, with a small knob in the center. When the string went out, the owner simply started turning the knob until the string came back on. Theoretically, once all of the lights were lit, the bad lamp could be easily located. The system worked by simply bypassing a different socket with each click of the knob, essentially shorting it out. When the socket with the bad bulb was shorted and therefore bypassed, the string would come on.

While the system worked quite effectively, the control box was large and heavy, making decorating difficult. A large tree with several strings of lights would have many control boxes, making the task of hiding them almost impossible. Add this to the fact that even with all of the strings lit, it was not so easy a task to spot a darkened lamp. This outfit was expensive, selling for three times what an "ordinary" light set sold for, and was soon discontinued.

1926

Several devices appeared on the market in the 20s, two of which are shown here. The idea was quite simple-by adding an extra lamp to a string of 8 lamps, the resulting voltage to each is lowered. The disadvantage is that the lower voltage dims the entire string. This method was actually quite popular, and many strings today can be found which have even had an extra socket or two spliced into the string.

1929

An attempt to solve the burnt out lamp problem in series wired sets came to us from Japan. Patented in 1929, the XL lamps contained a shunt device that allowed the rest of the light string to remain lighted should one or more lamps burn out. While the invention worked to keep the string lit, it was not successful from a practical point of view. When a bulb failed, the remaining seven on the string would receive considerably higher voltage, shortening their life. If the failed lamp was not replaced quickly, the stress on the remaining lamps soon took its toll. Genuine XL lamps are so marked on the glass envelope at the base of the bulb. There were also regular lamps made with the distinctive heavy embossed flame design, but they do not say XL on them. The Reliance company distributed the all of the XL branded light sets, although the Reliance name is seldom found on the boxes. Incidentally, the "XL" nomenclature referred to the lamps having "Xtra Life", as some of them were rated at 16 volts instead of the more common 14 or 15. Operation on normal household current of 110 volts resulted in the lamps lasting just a bit longer. XL lamps were used by other manufacturers as well, and sold under differing brand names.

Circa 1935 XL Lighting Outfit	Original patent for shunt type lamps	A look Inside the Box

Box of Westinghouse Mazda Detector Lamps	Close-up of lamp	A ca 1933 NOMA set advertising the use of the new Detector lamps.

1933

In the early 1930s, General Electric and Westinghouse sold Detector Lamps, quite a unique innovation in Christmas lighting. A typical series-type light bulb was filled with neon gas, so that when the lamp failed the string would still go dark, but the failed lamp would glow a bright orange. The glass envelope was slightly altered to make the new lamps easily discernable from the "common" type, and a twisted design was molded into the glass. To make it easier to locate the bad lamp, the bottom fifth of the glass envelope was left unpainted, so the glowing neon could easily be seen. This idea worked quite well, and for a time the lamps were good sellers. However, customers were unhappy about the glaring white light showing around the unpainted base when the lamp was operating normally. Once again, the Christmas lighting industry failed to please a demanding public, and the lamps were no longer made by the beginning of World War II. The set pictured above has the NRA stamp in it, indicating a manufacture date between the years 1933 and 1935.

1934

In 1934, Royal Electric came out with their new Tel-Tale outfit. Designed to help the consumer detect a burnt out lamp in a darkened string, this set had individual buttons at the bottom of each lamp socket. When pushed in, the button would short out the socket, thus effectively bypassing it. If the string lit, the bad lamp had been located. If not, one would move on to the next socket and so on. Technically, this set uses the same principle as does the earlier Detect-O-Light set discussed above, but eliminates the heavy control box. As you can guess, the task of pushing each button on several sets of lights on a dark tree was a tedious one, and this outfit was discontinued after just two seasons. This is a very hard set for the collector to find today.

1936

Again using lamps imported from Japan, this set of Perma-Lites was offered by AMICO. The lamps employed the same patented shunt device as did the XL lamps, but their shape was much closer to a typical C-6 type bulb. These lamps were apparently not as sturdy as were those of the XL variety, as the filament structure in these is a bit different and the glass is thinner. As with all of the shunt type C-6 miniature base lamps discussed on this page, it was no longer manufactured after World War II. This set is unusual in that it incorporates two independent strings of eight lights each, connected to a single plug. AMICO was purchased by the NOMA company during the war years, and NOMA used the name in their products that included imported lamps.