Updated 11-II-2017

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.

British Electric Lamps Ltd. (BELL)
Wimbledon Incandescent from 1965

Crompton
Guiseley Incandescent 96-Week Code

Duro-Test
Incandescent, Fluorescent & Fluomeric

General Electric
Edison 1880-1885
Thomson-Houston Lynn Factory from 1892
Incandescent Carbon Filament & GEM Lamps
Incandescent Tantalum & Tungsten Filament, 1910 - 1913
Incandescent 1913 - 1923
Incandescent 1924 - 1950's
Incandescent Stem Marking from 1940
Incandescent Stem Marking from 1964
Incandescent Etch Marking for IMG Machines
Incandescent Etch Marking for 3-Way
Incandescent Etch Marking for Lumiline
Incandescent Sealed Beam
Incandescent GE-Thorn Preston & Merthyr
Incandescent European Inkjet
Incandescent, Halogen, Discharge, Miniature & Fluorescent Mod-U-Line 96-month Code, from January 1908
Fluorescent Dot/Dash Code, from January 1970
Fluorescent Enfield 15-Dot Code
Fluorescent Enfield 8-Dot Code for USA Exports
Fluorescent Enfield Outer Box Code
Automotive & Minuature Leicester Code

Narva
Brand-Erbisdorf Fluorescent Lamps

Osram
Monthly Code, 1953-1973
Monthly Code, 1974-1994
Daily, Monthly and Quarterly Codes, 1994-Present

Osram-GEC
ELMA Code 1934-1957
Marconi Code 1958-1992

Philips
Roman Numeral System, 1917-1934
Roman Numeral System, 1917-1934 (in Dutch)
Weekly Code, 1928-1955
3-Cipher Monthly Code, 1934-1948 (note - for month symbols refer to 1949 Document)
3-Cipher Monthly Code, 1949-1957
3-Cipher Quarterly Code, 1955-1957
Domino Monthly Code, 1958-63
ELMA Code for British Philips Lamps until 1964
Factory Identification Symbols

Sylvania
U.S.A. Fluorescent 1940s-1950s
U.S.A. Fluorescent 1950s-1970s
Erlangen Fluorescent 1968-2008
Erlangen Fluorescent 2008-Present
Tienen, Charlestown, Lyon & Costa Rica
Manchester HID

Tesla
1967 to Present

Thorn
Incandescent 3-Character
Incandescent 6-Dot
Incandescent 11-Dot
Incandescent 12-Dot
Incandescent Photographic
Fluorescent 15-Dot for Atlas, Mazda, Ekco Brands
Fluorescent 15-Dot for Thorn Brand
Fluorescent 96-Month Code for 2D Lamps
Fluorescent Outer Boxes
Fluorescent made for Beacon
Fluorescent made for Claude
Fluorescent made for Crompton
Fluorescent made for GEC
Fluorescent made for Philips
Fluorescent Starters - Dot Code
Fluorescent Starters - Numeric Code
Mercury 11-Dot Code
Discharge & Halogen ELMA Code
Automotive & Miniature
Halogen Photocopier for Rank Xerox

Tungsram
Compact Fluorescent

Westinghouse
Incandescent 3-Way
Incandescent & HID
Fluorescent