Recently we've been shopping for light fixtures, and have noticed a dramatic increase in non-standard bulbs. CFLs in particular seem to be drifting away from the common threaded base, in favor of 2-post snap in bulbs.

I know there are efforts underway to remove incandescent bulbs from shelves, and I don't necessarily disagree with this. But I'm worried about having to find or keep on hand hundreds of different types of bulbs for my light fixtures rather than a consistent size and base.

So... Is the standard base becoming a thing of the past? Is a new standard clear on the horizon, yet? Should I try to stick with screw-base fixtures, or is diversity likely to be okay in the long run?

  • 1
    The "2-post snap in" is actually the GU24 bayonet connector.
    – dpollitt
    Nov 11, 2013 at 4:01

8 Answers 8


As of 2017, regulatory changes in the United States have obsoleted most of the answers here (and elsewhere on the Internet).

Short answer: Edison screw-type bases aren't going away.

The US Department of Energy no longer considers lamp base when certifying Energy Star luminaires and lamps. Lamp base can even be changed without having to re-certify the product.

The California Energy Commission mostly nullified its prohibition on incandescent lamp usage. Title 24 still requires "high efficacy luminaires" on new construction, but the definition expanded from luminaires that can only use fluorescent/LED lamps to luminaires that could use fluorescent/LED lamps. Notice that most luminaires include a free CFL; this lamp is necessary for the luminaire to meet the definition of high efficacy. The fact that the CFL can be swapped out for an incandescent lamp is now irrelevant.

The slightly smaller dimensions and quicker twist-lock insertion/removal of pin bases isn't enough to overcome the ubiquity of Edison bases. That's why GU24 bases are rarely found outside of specialty lighting stores. It's not uncommon for a luminaire with a GU24 base to be priced $20 more than the E26 variant.

  • Hello, and welcome to Stack Exchange. Cool answer: thanks! Jan 2, 2017 at 11:57
  • Thank you! That's an interesting way to make legislation supporting energy efficiency work with existing base designs. Of course, the user can just put an incandescent bulb in and toss the included bulb; but it's an attempt!
    – Scivitri
    Jan 4, 2017 at 17:22
  • The free CFL is usually worth the price you're paying for it. Feb 3, 2017 at 23:36

Many countries are banning the sale of incandescent bulbs over the next decade. Canada is planning on banning them in 2012 (not entirely sure if this is a done deal or not though), USA is banning them at different wattages starting in 2012 and ending in 2014.

The GU24 (two-pin) base is being introduced to force the transition, and prevent incandescent bulbs from being used in newer fixtures.

From this page:

What is a GU24 base and how is it related to CFLs?

  • The GU24 socket and base system is designed to replace the Edison socket and base in energy efficient lighting fixtures. The ENERGY STAR® Program Requirements for Residential Lighting Fixtures, Version 4.0 require that residential lighting fixtures cannot use the standard Edison screw base, even if they do not have a built-in ballast. The same requirement is included in California's Energy Efficiency Standards for Residential and Nonresidential Buildings, known as Title 24-2005. This requirement is designed to insure that fixtures that receive ENERGY STAR® qualification when using an energy-efficient self-ballasted CFL, or are qualified as energy-efficient under Title 24-2005 cannot be operated with an incandescent lamp. The GU24 socket was designed to be compatible with these energy efficiency regulations. The GU24 base has two dual-diameter pins; the smaller portion having a diameter of 3.4 mm (0.13 inches) while the larger portion has a diameter of 5 mm (0.2 inches). CFLs with a GU24 base are designed to be connected directly to the power line, so they are functionally equivalent to screw-base CFLs instead of normal pin-base CFLs. Unfortunately, ENERGY STAR® refers to CFLs with the GU24 base as self-ballasted pin base lamps, a designation that may lead to confusion with pin-base CFLs that do not have an integral ballast. Some manufacturers are also making modular ballasts with a GU24 base on one end and a socket for a normal pin-base CFL on the other. These modular ballasts can be used to adapt normal pin-base CFLs to fixtures that have the GU24 socket, thereby reducing the amount of material that must be thrown away when the lamp fails.

GU24 base

I would bet Edison will not disappear for quite a while though: there are hundreds of millions of fixtures, and it's not practical (or environmentally friendly) for everyone to go out and replace every fixture in the next few years. My guess (and I have no authority in the matter btw :)) is that it will be 2015-2020 before you start finding more GU24 base bulbs than Edison.

Also, you can get Edison to GU24 adapters, which means even if Edison bulbs themselves disappear, you can still use your existing fixtures.

Edison to GU24

  • 9
    This is a travesty! What will happen to all the "How many x does it take to screw in a lightbulb jokes?" Oct 27, 2010 at 13:38
  • 4
    That's outrageous. I want to go buy a bunch of CFLs and throw them at whatever government office came up with this nonsense. I've been using CFLs for years and LEDs for a year -- but they still don't beat standard bulbs for many applications. Oct 30, 2010 at 22:21
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    The thought of banning a light bulb truly shows how pitiful this country has become. If CFLs, LEDs, etc. save money without having to make any sacrifices, people will naturally prefer to buy them over incandescents. How many people out there want to buy an Atari or NES right now? Hardly any. But the next xbox, PS, etc. console will sell like hotcakes. The government stepping in and making demands about what people can and can't buy, when market forces would've taken care of the issue without any intervention, is a great display of how they love to feel powerful.
    – Michael
    Feb 1, 2011 at 11:36
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    I must note that the outrage is a bit premature. There's nothing in the above answer's reference that says that the Edison base cannot be used EVER. It's just that the EPA will not grant an Energy Star label to any device that has an Edison socket, and can thus accept an incandescent. So, once this goes into effect, if the fixture is Energy Star rated, it pretty much guarantees high energy efficiency compared to non-energy-star-rated fixtures, because you won't be able to put anything BUT an energy-saving bulb in. For the Edison base to be BANNED, an Energy Star rating must be mandated.
    – KeithS
    Sep 30, 2011 at 16:19
  • 4
    We've phased out gas lanterns but you can still buy them. As Keith states, codes are changing, recommendations are changing, seller and buyer incentives are changing and we'll eventually get through the CFL phase into the LED phase. But filament bulbs will always be an option. CFLs are the 8-track of light bulbs. They'll only be around for a few years. Then 95% of lights will be LED (ie the CD/MP3) and the other 5% will be all flavors of old fashioned incandescents (The Vinyl) savored by collectors and touted for their (arguable) 'superior quality'.
    – DA01
    Oct 1, 2011 at 5:32

Five years gone, here's the situation in America today: March 2016. Or rather, shops near Berkeley, California, which had a big hand in development of the CFL.

enter image description here

Target. Incandescent bulbs (tweaked to be somewhat more efficient with halogens and high-temp inner bulbs) are readily available, four for $5. Pretty close to the old 1980s price for quality plain bulbs, adjusted for inflation.

enter image description here

Target. Every fixture has an Edison E26 base, there are no GU24 fixtures in the store. Note they give you a free CFL with each fixture.

enter image description here

Home Depot. Every fixture is Edison or candleabra. Could not find any GU24s. They do not supply bulbs, and boxes talk like incandescents are normal, some acknowledge CFLs but have never heard of LEDs.

In individual bulbs, LEDs are rapidly elbowing out CFLs. They dominate the shelf space at CostCo and Ikea stopped selling CFLs last year. Most everything is either Edison E26 or candelabra, GU24 bulbs are scarce.

Edit: I did find a GU24 bulb. It was in a Habitat for Humanity ReStore, which is a sort of flea market for construction materials. It looks like it was new old stock some store donated because they couldn't sell it.

  • 1
    – cat
    Jun 22, 2016 at 12:21
  • 1
    Home depot offers GU24 bulbs and some other varieties in-store, and has done so for some time now. So does Lowes. I don't go to Target or Walmart to buy light bulbs; I use mostly fluorescent or LED. Jun 22, 2016 at 16:53
  • 1
    Of course. But I put my pants on and went there because shelf space is everything at a big box. It's centrally managed and fought-over by vendors. And it's just as I said - GU24s were conspicuously absent from the easily accessible shelves, and not one single display contained a GU24. The photo was not cherrypicked, it was typical. Jun 22, 2016 at 20:12
  • When I wrote this question, I was worried that government/industry would try to change bulb bases on us, and billions of light fixtures would become impossible to find bulbs for. I'm glad to see that attempt is failing, and we can keep fixtures that we have. Whether the GU24 is better, or design immovability is a good thing are deeper debates for another time. ^_^
    – Scivitri
    Jan 4, 2017 at 17:18
  • 1
    I think that GU24 had a single purpose, now obsolete since LEDs are actually good, and don't need sockets at all in built-for-LED fixtures. An oddball socket is still a good idea, since people are still over-lamping fixtures with limited heat removal. I prefer candelabra, and would change out GU24 sockets for that. It solves the overlamping problem because high power incandescent candelabras never existed, and high brightness LEDs are readily available at no cost penalty. Jan 4, 2017 at 18:27

This page on Lightbulbs Direct has information about the various types of fitting.

There are two main type - bayonet and screw.

Each of these has sub types, two for the bayonet, four for the screw cap.

In the UK it used to be pretty much exclusively the wider bayonet fitting that was used, with the occasional screw fitting just to confuse you. Other countries would have different fittings.

I think that with increased globalisation of manufacture and sales - which country doesn't have an Ikea! - we are seeing appliances and light fixtures from around the world being sold everywhere so there has been an apparent proliferation of fittings, rather than any one fitting being deliberately being phased out either by manufacturers or by politicians making laws.

What are being phased out (certainly in Europe if not worldwide) are incandescent bulbs in an effort to reduce the energy we use. In fact the compact fluorescent low energy bulbs are now being replaced by LED bulbs which have become more popular as the price lowers and as the colour of the light they produce has become "better" (for want of an objective term).

Just buy the bulbs you need for the fixtures you have.

  • Very informative link; I could wish they had a chart of bulb designation to pictures on store light-bulb isles. Most of those fittings I'm familiar with, and tend to be purpose-specific. But I've started seeing different bases in, say, standard size flushmount fixtures. The GU24 bulb prompted my question, which is a bulb I'd have to special order. And isn't on the page you linked although they look to be mentioned at the very bottom under CFLs. It looks like CFLs will be a much more diverse bulb type.
    – Scivitri
    Oct 26, 2010 at 18:12
  • Interesting that bayonet fittings are common in the UK. I have never seen them, except in cars. Oct 26, 2010 at 18:30
  • 1
    Bayonet used to be the standard in Australia as well but over the last 30 or 40 years ES has gradually become more common (probably due to imported light fittings) to the point where today it's about half and half. Oct 26, 2010 at 20:51

Until low-cost LED lighting is available, I'm afraid incandescent lighting is going to be a mainstay in my house.

I tried the compact fluorescent, bulbs. I really wanted them to win out, but frankly I didn't get the promised benefits for the extra cost. They burn out just as quickly if not more so than the incandescent bulbs in my experience. Also, the one major thing is that they are 99% guaranteed to break if you drop them, while their progenitors will bounce at least 75% of the time unless you drop them from a great height. I've broken so many of those stupid coiled fluorescent bulbs it just isn't funny.

  • A) You either had a small sample or bad luck. I've been buying CFLs for ten years now as I moved into bigger and better places and some bulbs are still with me after that whole time, while less than a quarter of what I've bought have burned out since then.
    – Sparr
    Oct 27, 2010 at 4:04
  • 1
    I went through about 25 bulbs. Very few of them lasted more than a year. I suspect, though, that they may be more sensitive to power surges. I live in a rural area where the power is a bit iffy sometimes.
    – JohnFx
    Oct 27, 2010 at 14:48
  • 3
    At home I've had great success with CFLs lasting forever compared to incandescents. Even in the worst locations (small spaces/no airflow, outdoors, and in places with lots of cycling). At work, it's another matter. We gave up on CFLs because we were replacing them monthly due to failures. All our other electronic equipment is fine though. Dunno. Something out there can kill CFLs real fast, hope somebody figures out exactly what it is so we can solve the problem! Oct 27, 2010 at 14:56
  • 2
    JohnFx: installing a whole-house surge protector may help. It could also be the brand of lights, they're not all created equally. Like you, I too, am waiting for lower-cost LEDs, but also more importantly, dimmable LEDs that actually work well. Many of my lights are dimmable, and frankly, dimmable CFLs are not that great.
    – gregmac
    Oct 27, 2010 at 14:57
  • 1
    If you don't leave them on at least 15 minutes, they can die much faster than they should.
    – Peter
    Oct 28, 2010 at 18:06

The california building code ironically is making it harder to use efficient environmentally friendly bulbs.

Where I would normally buy standard E26 base LED bulbs, my new fixture requires GU24 and comes with CFLs with this base. Now I have to get an adaptor back to the standard E26 bases, just to use the LED bulbs the mandate was supposed to encourage me to use in the first place.

It is ironic that the California mandate is pushing users toward inefficient mercury containing CFLs and making it harder to use the more efficient and environmentally friendly LEDs with better light quality.

  • 7
    Meh, everything causes cancer in California. I know that fact because it's prominently on every product I have to buy. Just waiting to get a carton of Organic Grass Fed Milk labelled with it as the warning is so pervasive. Anyway, that's the side effect of living in a nanny state that doesn't consider unintended consequences. Jan 31, 2016 at 5:42

I don't know about elsewhere but Australia is phasing out incandescent lighting - by law. Of course like so many other bits of legislation it was never thought through properly and many people have to replace light fittings because CFLs are larger than their incandescent equivalents and simply won't fit into the existing fittings. :(


The discussion covers mostly regulation, preferences and availability. Consider the practicality of the GU24. Have you ever twisted the glass portion free of a stuck Edison base that then is very reluctant to exit the fixture? A child or otherwise careless person won't shock himself inserting a finger or two into a live GU24 fixture.

  • Yeah, the GU24 is IP20, which is a plus. If only you could get bulbs for it! (and they hadn't left the all-important 3rd pin off, shortsighted nublets them all!) Apr 17, 2018 at 3:05
  • More a comment than an answer don't you think?
    – agentp
    Apr 17, 2018 at 11:51

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