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Green Communities

Let There Be Light — on the GU24 base for CFLs and LEDs

The GU24 lamp base means ONLY compact fluorescent lamps (CFLs) or light-emitting diode lamps (LEDs) fit, but any wattage works

A new type of two-pin lamp. Companies such as Maxlite are carrying a full line of Energy Star GU24 fixtures and lamps.
Image Credit: Maxlite

Are we really ready to say goodbye to incandescent light bulbs? The ones that give off 10% light and 90% heat? The ones with the shortest life span? The ones that have the lowest initial price, don’t flicker, are always instant on-instant off, and give off the “right” color and quality of light? Not so fast and not so easy…

We have been here before: 2- and 4-pin CFL fixtures!

Many of us have been here: wired a project with 2- or 4-pin CFL fixtures so that the lighting STAYED efficient when lamps (bulbs) needed to be replaced, only to hear complaints about the quality of the CFL pin lamps, the lack of wattage flexibility of the pin CFL lamps, the price of the CFL pin lamp replacements; or even worse, hear (at very high decibel levels) that there were no replacement pin lamps even being stocked by local retail.

GU24 base lamps are the future of energy-efficient lighting

I think we have it right this time: the relatively new GU24 base (see attached images). This new base has a 2-pin base that you simply twist and click to replace the lamp (bulb). It eliminates inappropriate incandescent lamp (bulb) replacement but allows replacement with ANY wattage of CFL OR LED. And the GU24 makes for a shorter base than the standard medium screw base (E26) so no worries over new CFL or LED lamps fitting into tight fixtures.

Are Energy Star and industry embracing the new exclusively CFL/LED GU24 base?

Yes, they are. As of this writing, the majority of Energy Star fixtures are using the GU24 base and there are a full range of CFLs and a growing number of LED lamps with the GU24 configuration, both in local retail and online. When I checked online, GU24 lamps of all types and wattages were widely available and our local True Value hardware store carries them. (The local Ace hardware store is not yet stocking them, but employees reported a growing interest and special orders for GU24 lamps).

Energy Star stated that the new draft of their GU24 product criteria will be out in early September of this year and the GU24 base is becoming more popular with LED lighting manufacturers as well.

What should affordable housing providers do about GU24?

In states with strict energy codes, you will probably be more and more “pressured” or motivated to consider GU24 — it’s the way to go, at least for new construction. In retrofit, depending on how the building code applies, you may want to go to GU24 as part of going green, moving your homes to GU24-base light fixtures.

The slightly higher first cost of a GU24-base CFL will be more than covered by the energy savings and longer life of the CFL compared to any incandescent bulb. And maybe you will want to offer rebate vouchers for GU24 lamps as a way of sharing your commitment to energy-efficient lighting with your clients.

What about LEDs and affordable housing?

LEDs are really not yet a good fit for affordable housing. While many lighting experts feel that LEDs are the bulb of the future and the LED market share is growing rapidly, LEDs are changing all the time and their first cost is still too high for the affordable housing market.

Most importantly, LED performance metrics need to change, to better separate out the LED wheat from the chaff. The new Energy Star product criteria for CFLs do a much better job in this respect, but LED product criteria are just not there yet.


  1. gusfhb | | #1

    In my renovation I took


    In my renovation I took great pains to make sure virtually all of the fixtures were edison I could use CFL's, it is hard to find cool looking lighting that isn't halogen. It is still impossible to find a real PAR16 bulb in CFL Some are comical, protruding 2 inches or more from the fixture

  2. ANDREA LEMON | | #2

    Very helpful, thanks!
    I was about to post a question to the Q&A section about what kind of fixtures to install in our new-construction Passivhaus, but you already answered me.

    We'll probably do a combination of LED strips for ambient lighting and then GU24 downlights for brighter task lighting. Does that make sense to you? Or should I go ahead and post my question to the Q&A section to get more input?

  3. 5C8rvfuWev | | #3

    You'd better send this to retailers, Peter
    Just forwarded your blog to my wife, who is thinking of lighting for a new house for us. She did a quick search on "Lamps Plus," one of the largest online retailers for fixtures of all sorts. They list only 13 items when she enters GU 24.

    I'm glad to be ahead of the wave, but what to do until the retailers catch up. Hmmm.

  4. zt88TUzzpw | | #4

    Evolving technology
    The GU24 base comes with it greater flexibility in options (CFL or LED) as well as ensuring that the bulb that will be used will be more efficient than the standard incandescent. As some users may have found, the offerings at present using this base may be a bit limited based on your location - but this is sure to grow. The fact that this base is more flexible than previous pin-based tech should also help to reassure those doing new construction or replacements that the GU24 base should be supported with lighting options for years to come. And while you point out that currently LEDs may not be as financially feasible for affordable housing, again the dual fitting of this base will make it so that lighting retrofits and installations can be done now with the GU24 base and CFL bulbs now - and replacements with LEDs later when prices fall further. Thanks for providing this great information.

  5. ANDREA LEMON | | #5

    fixture availability
    Joe, it looks like a lot of the fixtures from Rejuvenation are available with a GU24 socket. Most of the models shown come in multiple finishes and with many shade choices.

    [I've never ordered from them before, so I can't comment on the the quality or customer service.]

  6. kevin_in_denver | | #6

    High Volume means Lower Prices, so stick with Edison
    The standard edison base now has an affordable LED bulb:

    It's $10 vs. $7 for GU-24:


    It seems that you are sold on GU-24 because the consumer is forced to buy an energy efficient replacement bulb to fit the fixture. Well, that point is entirely moot with LED bulbs, because they are expected to last 20 years.

    This is also the best affordable housing option because the cost of bulbs for the resident is zero for 20 years, and energy costs are about the same as CFLs.

    Note the dimmable bulbs cost more:

    My wife thinks the light is better quality, also.

  7. Peter Yost | | #7

    Joel NG and search results on GU24
    Hi Joel -

    If you search with a space between GU and 24, you get 13 results; if you search without the space (GU24), you get over 180!

  8. Peter Yost | | #8

    PAR 16 - Keith
    I checked in with David Shiller from Maxilite and he stated that at only 2 inches in diameter, PAR 16 is really tough to do a CFL (Maxilite starts at PAR 20) so you really need to go to an LED for really energy efficient PAR 16.

  9. Peter Yost | | #9

    Stick with Edison - Keith Dickson
    Hi Keith -

    My own opinion is that we are not ready to move to just LED yet and the GU24 base allows us to move efficient lighting from quality CFLs to quality LEDs as the LED industry progresses. Even with CALiPer reports and the Lighting Facts label, it is still too hard to separate out the wheat from the chaff of LED lighting until after you have purchased. We all should be exploring LED options, but I don't think we or the lighting industry is ready to move en masse to LEDs for energy efficient lighting. And certainly for affordable housing (the target industry for this particular blog), the CFL holds court for now.

    By the way, stay tuned: BuildingGreen's GreenSpec (which is the base for Green Products in GBA) is working on performance criteria to drive GreenSpec LED lighting.

  10. gusfhb | | #10

    truthfully I have LED
    truthfully I have LED undercabinet, 5 led par16[sylvania at the despot for 13 bucks] but otherwise LED is not quite ready for prime time. My opinion is stick to edison as that is where the cheap bulbs will be for a very long time. Unless you expect everyone to have a basement full of 60 watts, trust them to buy CFL, don't try to force them.

    Big problem: halogen fixtures, locked into wasteful bulbs. I managed to only end up with one, but it is a doozy, 300 watts in the downstairs bath, I pretend to not notice that 2 of the 6 bulbs are burnt out. Upstairs bath is also halogen,but candelabra base, so there is hope. Otherwise the entire property is CFL or LED, except 2 garage door openers that have not burnt out since I bought the place

  11. wjrobinson | | #11

    Of course anyone can just buy
    Of course anyone can just buy adapters...

  12. Ted Clifton | | #12

    Changing from the Edison base is just plain silly!
    Changing the base from what 99.9% of America has is just plain silly. You may be able to force builders to install GU24 base fixtures in new construction (the Washington State Energy Code requires 50% pin-based fixtures), but at best it will take about 100 years to convert everyone to 100% CFL using that strategy. Australia outlawed the incandescent light bulb several years ago, and with the exception of a few specialty bulbs, they are done with them already.

    Changing the base does nothing for the efficiency of the product. I have had customers remove brand new pin-based fixtures from their homes, and replace them with cheap garbage fixtures, just so they could buy bulbs for them at their local grocery store! (Yes, that is where 99% of America buys their light bulbs!)

    The right way to fix this problem is to change what is available at the store, not what is at the base of the bulb.

    Finally, how many energy nerds does it take to screw in a light bulb?

  13. user-827869 | | #13

    GU24 base bulbs
    I disagree. 99% of all fixture in homes today are medium base bulbs. The efficacy of a CFL is the same as an equivalent GU 24 base. Except the GU 24 light cost $10 at home depot and the medium base CFL are free at the local PUD or less than 2 dollars in any store. I have replaced 4 out of 12 GU24 bulbs in a kitchen remodel I did last summer. It is a weekend Cabin with very little use. I think the GU24 will disappear after the incandescents are outlawed.

  14. Ted Clifton | | #14

    Allan Marshall has it right!
    'nuff said!

  15. kevin_in_denver | | #15

    Response to Ted Clifton
    400. One to screw it in, and 399 to blog about it:

  16. rXu8mBJqEY | | #16

    GU24 will be a flop
    With the regular medium (E26) base CFL bulbs now under $1.00 and/or free with your electric company, GU24 will not be used. Allen Marshall's post is dead one and GU24 will be a flop. GU24 bulbs cost 5X as much as CFL bulbs so my new light exterior fixtures that I got on clearance will be modified so they can use a medium base CFL bulbs. Once LED's come more affordable, I'll switch my CFL's to LED's that will still use the medium base.

    I wish the GU24 to E26 adaptors were more affordable so I don't have to modify my light fixtures...oh well....I'll be saving $4.00 per fixture.

  17. 3S9ACRCJtN | | #17

    GU24 in the future
    Actually, the point is lost when we start talking about retrofitting back to the Edison base. Yes, the whole point of the GU24 is to eliminate the incandescent option, and in some places (notably Calofornia), this is a matter of legislation. CFLs are getting better all the time, and in my experience, GU24 based CFLs are rapidly approaching the cost of Edison based retrofit lamps (and the argument that one can get these free, or almost, from the local utility company is avoiding the truth that this is only because of artificial government subsidies). As a lighting designer, I have been aware for years that the incandescent is on its way out. CFLs are here for the foreseeable future, and beyond that, more affordable LEDs will be the ascendant technology. There really is no reasonable argument for the A19 anymore, except as a romantic flash from the past.

  18. distalis | | #18

    Gu24 base is the future??? The year is 2020 and GU24 is a complete and utter failure. Bulbs are expensive ($7 a piece) and wattage is limited. I am effectively stuck with 13W bulb because I am not allowed to change a light fixture in a rental building. So much for "bright" future

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