Miniature Christmas light sets changed over the years to adapt to stricter safety standards.
By knowing this you can determine when your set was made.

Start by examining the plug.

1 - Non fused pre 1977. 2 - Fusible link 1977 - 1990. 3 - Replaceable fuses post 1987.
(Roll cursor over photo)

Photo 1 shows a non fused plug used prior to 1977 marked "15A 125V JAPAN".
This type of plug was used on miniature light sets before fuse protection was required.

Photo 2 shows a fusible link plug used from 1977 to present, mostly on the cheap sets. It is marked "Current rating 1A, fuse rating 3A, 125V"
On this type of plug there is no door to access the fuses. That's because there are two non replaceable fusible links inside the plug.
A fusible link is a short length of fuse wire inside the plug that provides over current protection.

Photo 3 shows the now standard plug with replaceable fuses, used from 1987 to present .
This plug is marked "use only 3A max 125V fuse". Roll your cursor over the photo to open the fuse door.
Inside this plug are two replaceable 3.5 millimeter diameter by 10 millimeter micro fuses, typically 3 amps.
At the same time Underwriters labs introduced the silver holographic certification tag. The hologram is visible in blue.

Now examine the sockets

1- Spliced connection.
1950s ?

2- Wire wrapped contact
Pre 1977

3- Crimped contact

Photo 1 In some early miniature sets, there were no sockets, the bulbs were spliced directly to the wires!
From the Cactus lights set. This design is found on early imported miniature sets made around the 1950s to 1960s.

Photo 2 shows an old style socket with the wire simply wrapped around the contact, which is then inserted into the socket.
From the 15 light Yuletide set. This design is typical of sets from Taiwan made before 1977.

Photo 3 shows a socket with crimped contacts. This was required due to safety regulations that specified that the wire and insulation be solidly attached to the contact. The contact is also barbed, or shaped so it cannot easily come out of the socket.

Now examine the Bulbs.

1- Drawn Tip 2- Arched Filament 3- Kinked Filament 4- Vertical Filament

The design of the bulbs also changed over the years.
Starting from the left, bulb #1 is an early miniature bulb that has the exhaust tip drawn out into a point, which presented a safety problem.
If you smacked your hand down on the bulb, it could puncture your skin! This design was discontinued around 1977, maybe earlier and changed to the short ball tip seen in bulbs 2, 3, and 4.
Next, bulb #2 is an old school bulb, with the filament strung horizontally and formed into an arch. The problem with this design is that the filament would sometimes kink, as seen in bulb #3. This resulted in reduced light output, hot spots, and shortened life for the other bulbs in the string.
Bulb #4 is a modern design introduced first on the better brands like G.E. then others later with the filament strung lengthwise. This solves the previously mentioned problems.

Here are some more tips to help in dating the vintage of a set.

ZIP codes were introduced in 1963 and the ZIP+4 code in 1983 for decorations sold in the U.S.A.
U.P.C. bar codes were invented in 1973 and introduced in 1974 but did not gain widespread use until a few years later.
Source : Wikipedia

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Bulb base identification.

Miniature Christmas light bulbs were made in a variety of base designs over the years.
The chart below identifies the ones I have come across.

1/4 inch wedge base.
This is the most common base style in use.
The 1/4 inch diameter refers to the round part of the base that enters the socket.
7 Millimeter wedge base.
Used on sets made to metric standards, it's slightly larger than the 1/4 inch size shown above.
7 Millimeter wedge base with locking clip.
The tab keeps the bulb from coming loose from the socket.
Italian lights by Kurt S. Adler.
Used on "Fairy Lights" made in Italy this style is smaller than the typical base at 5.5 millimeters, or 7/32 inch in diameter, with an oval shaped contact section.
The entire bulb is only 24 millimeters, or 15/16 inch  long.
Santa's World  by Kurt S. Adler.
This base is unique because the wires are bent against the narrow part of the wedge, rather than the wide part.
1/4 inch wedge base with tail.
Used on heavy duty and constant on sets, the tail is added to keep the contacts in the socket from shorting against each other. If a bulb should come out, the contacts in the socket close to maintain current flow.
General Electric Merry Midget 1963 - 1978.
A variation on this 2 pin base was also used on NOMA miniature sets.
Another variation on the 2 pin base, this one has square pins. Manufacturer not known.
Combination wedge base/ reflector, NOEL standard, petal style.
The most popular reflector style, it resembled a miniature Tulip flower.
Combination wedge base/ reflector, NOEL standard, petal style.
This one has finer petals and is called a badminton reflector.
Combination wedge base/ reflector, NOEL standard, star style.
This reflector was more resistant to breakage, but the points would snag on the wires and stepping on it in stocking feet was quite painful !
Combination wedge base/ reflector, NOEL standard, fluted style.
This style reflector was used exclusively on tree toppers.

Identification of Edison base bulbs.

Brass Base
1920s to present.

Aluminum Base
1957 to present.

Nickel Base
1990 to present.

For Edison base bulbs you can tell when they were made by knowing what metal the base is made of.
Brass Base - Used throughout the history of bulb making, but today used mostly on lesser quality brands because brass tarnishes easily.
Aluminum Base - Introduced by G.E. and Westinghouse in the late 1950s. More resistant to corrosion, Aluminum is a dull silver color.
Nickel Base - Introduced about 1990 by G.E. and others, has excellent resistance to corrosion. Nickel is a bright silver color.

The next page showcases vintage sets.

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