I have a Japanese F20T10 tube in my collection. It is slightly shorter than a standard F20T12. I got it out from a old desk lamp. In my opinion, they were dimmer than a F20T12.

I have a Japanese F20T10 tube in my collection. It is slightly shorter than a standard F20T12. I got it out from a old desk lamp. In my opinion, they were dimmer than a F20T12.

The line voltage in Japan is 100v.  I know that F20 is usually ran with a choke ballast.  Perhaps they made it slightly shorter so it will start and run reliably on 100v mains with a series choke ballast without needing a step-up transformer type ballast? 

In Europe, F40T12/F36T8s are ran on series choke with a starter. That setup works on 230v mains, but not with 120v. 

When my father was in the Army and we were on Okinawa, I got a dual 20 watt fixture. When I got back here (this was in the 1960's) I had to move the sockets back for US made 20 watters to fit. It wasn't very much, so I don't think the voltage thing was a problem. I had a "National"  bed lamp that was preheat and I always wondered why the bulbs didn't last as long as I thought. When I was at Clemson University in 1966 the ballast shorted, and I had to find another. I got a trigger start one and it was fine after that. Yeah the 100V ballast on 120 something volts for awhile and it gave up.  Stunk up the dorm room too and blew out the filaments on the lamp....