Author Topic: E26 or E27?  (Read 1349 times)
Emersyn
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E26 or E27? « on: October 17, 2024, 03:29:59 PM » Author: Emersyn
I commonly see the denotation of E26 or E27 on common bulbs, but which one is the 'correct' or 'official' one?

I personally use E26 since I just like the number better.
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Re: E26 or E27? « Reply #1 on: October 17, 2024, 03:34:32 PM » Author: dor123
The "Medium" edison screw is E26.
The European standard edison screw is E27.
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Re: E26 or E27? « Reply #2 on: October 17, 2024, 05:54:02 PM » Author: Emersyn
Ah, it seems they are kind of intermixed now...
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Re: E26 or E27? « Reply #3 on: October 18, 2024, 02:17:47 AM » Author: Medved
They are practically the same thread, but there are quite a few differences in the standardized dimensions around the socket area, like adjacent bulb neck, the length of the thread-less section of the cup between the thread and the bulb, the socket design,...
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Re: E26 or E27? « Reply #4 on: October 18, 2024, 06:05:47 AM » Author: Emersyn
Ah, good to know-

My grandparents have a lamp that somehow became E28 or E29. I found a piece of foil in that lamp to try and help it, it was quickly removed!
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Re: E26 or E27? « Reply #5 on: October 18, 2024, 02:45:29 PM » Author: RRK
In my experience, American-spec E26 lamp generally fits in E27 lampholder, but requires a bit scary force to fit completely )

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Emersyn
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Re: E26 or E27? « Reply #6 on: October 18, 2024, 02:56:53 PM » Author: Emersyn
Enough force to break the glue on an incandescent lamp?
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Re: E26 or E27? « Reply #7 on: October 18, 2024, 03:24:09 PM » Author: RRK
No probably, but a tight fit and some scary cracking sounds :) I did this with an American made E26 70W Philips CMH lamp and ceramic E27 lampholder.
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Emersyn
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Re: E26 or E27? « Reply #8 on: October 18, 2024, 03:46:49 PM » Author: Emersyn
Wait if E26 is smaller than E27, why is it hard to fit it?
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Re: E26 or E27? « Reply #9 on: October 18, 2024, 04:48:42 PM » Author: RRK
Lamp base geometry is defined by international standard IEC 60061-1. With a brief look, there are some subtle differences, thought thread pitch is the same as 3.629 mm or 7 threads per inch, thread radius is large in E26. Also, E27 end is more conical with higher vitrite insulator, and E26 end is flatter.

IEC 60061-1 is a commercial document, but Russian GOST standard that copies this IEC is freely available. You can get it here. https://meganorm.ru/Data2/1/4293763/4293763209.pdf

Look at the drawings on pages 53 and 55.

I am attaching screenshots of these.


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Emersyn
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Re: E26 or E27? « Reply #10 on: October 18, 2024, 05:13:55 PM » Author: Emersyn
Ah I see slight differences now-

Thank you to all who helped answer!
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Re: E26 or E27? « Reply #11 on: October 20, 2024, 09:59:25 PM » Author: wide-lite 1000
 @Emersyn  : If the lamp socket is indeed an E-29 I'd save it in a heartbeat ! E-29 (Ad-Medium) is VERY rare !
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Re: E26 or E27? « Reply #12 on: October 21, 2024, 06:00:36 AM » Author: Emersyn
I will check it next time I'm there-

It is in a normal table lamp, so wouldn't think it is anything crazy, but I'll see in December!
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Re: E26 or E27? « Reply #13 on: October 23, 2024, 12:08:25 AM » Author: Michael
For some odd reason my very first blacklight incandescent bulbs 75W 220V in my childhood had always a strange lamp base which as I remember was shorter in length, a bit different looking and  also the bulbs neck was flush to the base like those A19 incandescent bulbs in the states. I also remember that it did not light in all sockets because it was just short to make contact in some regular E27 sockets. My guess they back then (in the 1980s) imported these bulbs to Switzerland with E26 bases but right voltages.

To me as an European the E27 looks better and very familiar on any bulb than the somewhat shorter E26. That‘s simply because I grown up with them. I think that the E27 derivates from the E26 since Edison is the inventor of that type of bulb fixation.
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Re: E26 or E27? « Reply #14 on: October 23, 2024, 03:38:15 PM » Author: Emersyn
Later I must compare my Tungsram cap to some random American caps for comparison!
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