Light fixtures of some sort have been around for centuries, or perhaps longer, fulfilling the need for accessible lighting since the first permanent homes were built. Several indicators help determine whether your light fixture is an antique, a reproduction or simply a light inspired by old styles. Check for wiring, gas tubes and markings on the sockets to narrow down the age range of the fixture. If the fixture looks brand new and has modern wiring, it is most likely a reproduction and not an antique.
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Wiring, or Lack Thereof
Check the fixture for bits of wiring, if it is an electric light fixture. If the fixture is antique, its wiring is as well, unless it went through an upgrade at some point. Antique wires may look old, yellowed or frayed, and they typically feature a cloth coating, rather than the plastic material covering modern electrical wires. If metal tubes exist in place of wires, the fixture may be a gas lamp. In some cases the wiring may have been removed from the fixture entirely, even though it is an electrical fixture; in other words, it may not be a gas fixture just because it has no wires.
Electrical Code Markings
The socket for the light bulb is a good indicator of a light fixture's age thanks to laws requiring electrical ratings to be clearly marked upon them. Inspect the outer parts of the socket or the socket itself for lettering. Electrical codes have required markings since 1899; if the socket has no markings whatsoever, it may date to before the 1900s. A socket from 1899 to 1910 is rated by candlepower rather than watts; a socket from this era may have "50 C.P." stamped on it, which means 50 candlepower. All sockets from 1910 and beyond have a wattage rating on them instead.
Pull chains have been around a lot longer than you may expect; the earliest date back to the late 1890s. While the chains themselves haven't changed much in over 100 years, the finials or adornments at the ends of the chains vary based on manufacturer, trends and eras. Several versions of acorn-shaped finials are found on chains from the early era of electric lamps and light fixtures. If the fixture has an acorn-shaped chain finial, it is most likely from 1930 or earlier. Modern chains have a tassel-style pull at the end, typically shaped like a fluted flower. Versions of this tassel date back as early as 1910. Some manufacturers used ornate ball-shaped finials or snap-on pieces; compare the pull on your light fixture to charts on collectors' sites to determine an age range.
If your light fixture has its original glass shade or ceiling-fixture cover, it may help determine whether the fixture is an antique. Painted glass orb-style shades, typically featuring floral designs, were used on some fixtures, lamps and even oil lamps. Inspect the shade carefully to ensure the design feels like paint; if it's painted, brushstrokes should be evident. Modern reproductions use decals instead, which leave a completely smooth surface over the entire design area. If the shade looks old and outdated compared to similar modern shades, it most likely is an older piece. Compare the shade to listings on auction sites or antique-lighting websites to get an idea of the shade's age. Some antique shade styles are still made as reproductions for old lamps; ask an expert such as an antique dealer to be sure the shade and fixture are antiques if you are unable to determine this on your own.