Light Bulb Base & Lighting Specs Reference
Look up common bulb bases and lighting markings such as E26, E27, GU10, G9, lm, K, W and V before replacing a bulb.
Data last maintained
Light Bulb Base & Lighting Specs Reference
Look up common bulb bases and lighting markings such as E26, E27, GU10, G9, lm, K, W and V before replacing a bulb.
Data last maintained
About Light Bulb Base & Lighting Specs Reference
Bases, markings and fixture checkpoints
The table covers common household bulb bases and package markings. It explains what a code usually refers to, where it is often seen, and which fixture labels still need to be checked before use.
Search by code, marking or use case
Search E26, E27, GU10, 2700K, lumens or other visible text, then narrow by base family or fixture use. The result keeps the code, size idea, common use and caution points together so the label can be checked without jumping between articles.
Not wiring, retrofit or shopping advice
A matching base code does not guarantee electrical safety, dimmer compatibility, heat clearance, ballast compatibility or a legal retrofit. Confirm critical work with the fixture label, device manual, product maker or a qualified electrician.
FAQ
Common questions and answers about this topic.
Are E26 and E27 bulbs interchangeable?
They look very similar, but the base code alone is not enough. Check the fixture label, voltage, wattage limit and product documentation before treating one as a substitute for the other.
What is the difference between GU10 and GU5.3?
GU10 is a twist-lock base with 10 mm pin spacing and is often used on mains-voltage spotlights. GU5.3 or GX5.3 has narrower 5.3 mm pin spacing and is often tied to MR16-style lamps that may use a separate low-voltage driver.
Should I compare lumens or watts when choosing brightness?
Use lumens for brightness. Watts describe power input and are still important for the fixture maximum, but modern bulbs can produce similar light output with different wattage.
What does 2700K or 5000K mean on a bulb?
K is Kelvin color temperature. Lower values such as 2700K usually look warm and yellowish, while higher values such as 5000K look cooler and whiter or bluer. It is not a brightness measurement.
Does a dimmable bulb work with every dimmer?
No. Dimmable means the bulb is designed for dimming, but the dimmer type, driver, load range and fixture still need to be compatible. Check the manufacturer guidance before use.
Can this table tell me whether a bulb is safe to install?
No. It helps read visible codes and markings only. Safety depends on the fixture, wiring, voltage, heat clearance, controls and local rules. Confirm installation or retrofit questions with the manual, product maker or a qualified electrician.
Data Sources
This tool's data is compiled from the authoritative sources below.
- NEMA - ANSI C81.61 lamp bases contents and scope(opens in a new tab)
- NEMA Standards Action - ANSI/NEMA C81.61 revision notice(opens in a new tab)
- ENERGY STAR - Light Bulb Purchasing Guide(opens in a new tab)
- U.S. Department of Energy - Purchasing Energy-Efficient Light Bulbs(opens in a new tab)
- ENERGY STAR - Light Bulb Purchasing Checklist(opens in a new tab)
Data last maintained