GU24 bulbs and sockets
The North American twist-lock base reserved for energy-efficient lamps
GU24 is a twist-and-lock lamp base with two pins 24 mm apart, used in North America on fixtures meant only for energy-efficient lamps. Each GU24 lamp carries its own LED driver or fluorescent ballast, and no ordinary screw-base incandescent bulb fits the socket, so the fixture stays efficient for life.
Energy codes had a problem with ordinary sockets: a builder could install an efficient fixture, and the next owner could screw in a 100 W incandescent bulb. The GU24 base, introduced in the 2000s, solved it by reserving a socket for lamps with built-in electronics. It is common in North American homes built to energy codes, especially in California.
Why GU24 exists
GU24 lets an efficient fixture stay efficient. North American energy codes, led by California's Title 24, required high-efficacy lighting in some rooms, and a screw-in socket could not guarantee it. GU24 sockets take only lamps with their own driver or ballast, first compact fluorescents and now LEDs, so an incandescent bulb cannot be fitted later.
Common lamp bases, drawn to the same scale
10 mm
The base is a cousin of the GU10: two pins with rounded heads push into the socket and lock with a twist, but the pins are 24 mm apart. Now that LED bulbs have replaced incandescents in ordinary sockets too, the base matters less for energy than it once did, but many homes still have GU24 fixtures that need GU24 lamps.
GU24 vs E26
An E26 socket accepts any bulb with a medium screw base, efficient or not, while a GU24 socket accepts only GU24 lamps with built-in electronics. E26 bulbs are cheaper and come in far more styles; GU24 lamps cost more and are stocked less widely, so check availability before choosing GU24 fixtures for a new project.
Adapters exist in both directions. One with an E26 screw and a GU24 socket lets a GU24 lamp go into an ordinary fixture. The reverse, a GU24 plug with an E26 socket, lets any screw-base bulb into a GU24 fixture, but it defeats the energy code the fixture was installed to meet, and it adds height and weight the fixture was not designed for.
GU24 is not G24 or GX24
The names are close, but G24 and GX24 are plug-in bases for pin-type compact fluorescent lamps, mostly in commercial downlights, and they need a separate ballast in the fixture. GU24 is a twist-lock base for complete self-ballasted lamps. Check the full code, including letters such as d or q, before ordering.
G24d lamps have two pins and a starter in the base, for magnetic ballasts; G24q lamps have four pins, for electronic ballasts. LED replacements for both come in plug-and-play and ballast-bypass versions, much like LED tubes.
Choosing LED GU24 bulbs
LED GU24 lamps come in the familiar shapes, A19, BR30 reflectors and globes, so choose the shape the fixture was designed for, then the lumens, color temperature and CRI as for any bulb. For dimmed fixtures pick lamps marked dimmable, because some GU24 lamps, like the CFLs before them, are not.
A spiral CFL in a GU24 fixture can be replaced directly with an LED GU24 lamp of similar lumens: a 13 W CFL gives about 800 lm, like a 60 W incandescent, and an LED lamp does the same with 8–9 W (see choosing by lumens).
Frequently asked questions
Can I put a regular bulb in a GU24 socket?
No. A GU24 socket takes only GU24 lamps, which have built-in electronics. Adapters for screw-base bulbs exist but defeat the purpose of the fixture.
Are GU24 bulbs LED?
Most sold today are. The first GU24 lamps were compact fluorescents; both types carry their own driver or ballast in the base.
Are GU24 and GU10 the same?
No. Both twist to lock, but GU10 pins are 10 mm apart and GU24 pins 24 mm apart. GU10 is for spotlights, GU24 for general household lamps.
Is GU24 used outside North America?
Rarely. It was created for North American energy codes; most other countries regulate the efficiency of the bulbs themselves instead.
Sources and further reading
- ANSI C81.61, Electrical Lamp Bases: Specifications for Bases (Caps) for Electric Lamps (GU24).
- IEC 60061-1, Lamp caps and holders together with gauges for the control of interchangeability and safety: Lamp caps (GU24, G24 and GX24 caps).
- California Energy Commission, Building Energy Efficiency Standards for Residential and Nonresidential Buildings (Title 24, Part 6), residential lighting.
- UL 1993, Self-Ballasted Lamps and Lamp Adapters.
Image credits
- GU24 LED lamp: Cree, Inc., via Flickr, CC BY 2.0. Base chart: LEDlights.org.