Hey guys, how’s it going? Hope everybody’s having a good summer. As simple as this sounds, I’ve always been fascinated specifically with twin tube PL fluorescent lamps. When I was a child and visited a local electrical supply store with my dad, they had a Phillips unit with a 9w tube, maybe seven or 8 inches long warm white and it plugged into a preheat square maybe 3” x 3” ballast that also had a screw base to go in a socket where a normal incandescent bulb would go.. the tube had the very small junction at the top may be a half inch down, it was not a full same diameter loop like some are designed. Later on maybe 20 years down the road when I was at an aquarium shop I hung out at and noticed that they were selling what was called power compact and it was a giant version of these up to about 3 foot long rated at about 96 W. They had a 54 W version maybe a 36 W an 18W and then the little 9w same darn bulb. But they were tuned for the proper colors for plant or coral growth. I thought that was pretty neat that somehow these became adapted. Previously they were using T 12 and T 12 VHO and or with metal halide I believe they were short-lived however T5 fluorescent took over to replace these, and finally LED, which is what they’re using now it seems like. For some reason these plug-in florescence still fascinate me and I was always wondering if they are burning at high output or VHO levels of intensity or are they simply just a T5 bulb bent in half. I guess some T5 run HO and some run NO also. Maybe this is the same with the Phillips aka aquarium power compact. The largest bulb I believe was 34 inches had a T5 profile and burned at 96W (rating at least). It had the same tiny junction about a half inch down from the top, which I remember the shop breaking accidentally multiple times while placing in the clips.. just kind of curious to the history of these if the large version was ever used anywhere else or was that specifically an Asian clone may be made with phosphorus for coral growth that came and went. As far as I know there’s leftovers around, but they’re no longer in production. I’ve never seen them in any other fixtures that size. My first little PL fixture I had gotten was in the late 1980s and they look completely identical. I’m assuming Phillips brought them out and then other people took it and ran with it. Just looking for any tidbits of knowledge and info  to help me to understand them better, thanks guys!!! Just a curiosity and geek and me. also kind of surprised that that little tiny arc jumper hole at the end, works and seems to work, as well as when the tube makes a full smooth bend. Something beautiful about these, especially the ones that combine two colors for the marine life. I’m assuming they were all made by a company Asian, probably who took the Phillips design and just made these for aquariums.

The P in PL stands for the Greek letter pi (the same one that is equal to 3.14156 in math). The bridge is in fact so that the arc can get from one electrode to the other. These are in fact very similar in concept to a U-bent fluorescent lamp. The pi design with the bridge like you describe was a Philips patent back in the day. That meant that Sylvania/Osram and GE/Tungsram couldn’t make them. So they came up with their own designs. Sylvania/Osram had more of a U bend at the very end but it had square corners at the tip. GE/Tungsram had sort of a hybrid of the other two, sort of a bridge like Philips but almost at the end and square-ish corners.

I quite like them, I have one in the kitchen in an under cabinet fixture and one as a night light in the basement, among others.

Thank you for that info! That’s really interesting!