Lamp Markings

It is customary to mark lamps with information concerning their date of production and the manufacturing site, which can be of great value to aid in the identification of historic examples. The markings are sometimes applied in coded format owing to the limited space available, as well as to avoid the necessity for frequent changes of the marking plates.

Historically these codes were written by hand in indian ink, either on the glass stem inside the bulb or on the outside of the bulb in the area that is covered by the cap. Increased production volumes led to the code being embossed into the glass stem press, and later still to be etched into the glass bulb along with the manufacturer's brand and rating details. Other frequently used techniques are to emboss the code into metal or plastic caps, or to mark other internal lamp components. More recently, inkjet and laser techniques have become commonplace.

The codes are not always easy to decipher without studying large quantities of lamps. Several companies have kindly made details of their marking systems available to collectors and other enthusiasts, and the list below details those which have become available in the public domain.