Fortunately, there are standards in the lighting industry where parts are built to spec. Pieces of an older lamp that fail can be replaced with an almost exact replacement part. Worn out sockets and switches can be replaced. Bulbs are manufactured to meet these same standards to fit the socket.
Bulb Shapes Explained
Bulb shapes are difficult to explain. The standards for bulb shape relate to the width, height, and curvature. For an A-19 bulb the A parts describes the shape and the 19 is the size of the bulb. For the A series bulbs, the width is measured in 1/8 inch and an A19 is 2 3/8 inch wide ( 19 times 1/8 inch).
|A-19, Standard base, all purpose house and appliance bulb|
Other bulb shapes like the G, PS, CT, or T all describe the shape and the corresponding number is the size. These standards are part of the ANSI C79.1-2002 Nomenclature For Glass Bulbs Intended For Use With Electric Lamps. If you want to learn more, good luck with that journey.
Socket Sizes ExplainedSocket sizes follow a simpler rule of Type-Size. E type sockets are the most common. The E stands for Edison and designates a screw type socket. The size is a simple measurement of width in millimeters. An E26 socket (most common type) has an Edison thread interior and is 26 millimeters wide. This socket is also referred to as a Medium socket.
|48226 - 3" Medium Base Keyless Candle Socket|
|Designation||Base major diameter (thread external)||Name||Application||IEC 60061-1 standard sheet|
|E5||5 mm||Lilliput Edison Screw (LES)||Indicator lights, decorative lights||7004-25|
|E10||10 mm||Miniature Edison Screw (MES)||Flashlights, bicycle lights||7004-22|
|E11||11 mm||Mini-Candelabra Edison Screw (mini-can)||120 V halogen mini-candelabra||(7004-6-1)|
|E12||12 mm||Candelabra Edison Screw (CES), C7||120 V candelabra/night lamp||7004-28|
|E14||14 mm||Small Edison Screw (SES)||230 V candelabra/chandelier, night lamps, and some pendant lights.||7004-23|
|E17||17 mm||Intermediate Edison Screw (IES), C9||120 V appliance||7004-26|
|E26||26 mm||[Medium] (one-inch) Edison Screw (ES or MES)||Standard 120 V lamps||7004-21A-2|
|E27||27 mm||[Medium] Edison Screw (ES)||Standard 230 V lamps||7004-21|
|E29||29 mm||[Admedium] Edison Screw (ES)|
|E39||39 mm||Single-contact (Mogul- in America) Goliath Edison Screw (GES)||120 V 250+ W industrial||7004-24-A1|
|E40||40 mm||(Mogul) Goliath Edison Screw (GES)||230 V 250+ W industrial||7004-24|
California requires remodels and new construction use a GU24 (bi-pin) socket. These types of sockets require matching bulbs and maybe limited to CFL or LED bulbs. Traditional sockets can be adapted to GU24 sockets with a simple adapter.
|48707 - Medium Base E26 Socket to GU-24 Socket Adapter|
Some Standards Don't ApplyAs always, there are some exceptions to the rule. One exception might be a failed swivel on an old lamp. No matter how hard you try, the replacement piece does not exist. This is true, but swivels, arms, bodies, and bases are decorative features and not electrical parts. The standards for these parts are part of the thread sizes. A different topic.
Another complaint might be related to a European fixture. Maybe it has bayonet sockets or a strange size thread socket. Standards are still in play but are subject to regional preferences. Some older European fixtures have E17 Intermediate sockets. If you are in the process of a repair for a US market, convert the sockets to E12 Candelabra since these bulbs are easier to find.
|47624 - Single Contact Brass Bayonet Socket With 1/8IPS Male Thread|
This article only scratches the surface of bulb and socket standards. We didn't touch Wattage, the measurement of energy consumption for bulbs. We also didn't cover specialty antique style or decorative bulbs shapes and styles.
What you can do with this new found knowledge? We suggest using it for light conversation at your next dinner party.