Hey guys, when my dad and I used to keep saltwater fish back in the 90's a grandmother like figure/shop owner of mine whom had taught me all I knew of saltwater i stayed close with as she sould pretty much let me stay at her shop on weekends and summers to help and learn. Later well after dad and i got out of the hobby (she stayed in buisiness for a few more years) she told me of this new technology (around 2004) called Power Compacts that were replacing Metal halide (my all time favorite for corals that I could never afford at the time) and regular NO bulbs (what I could afford).  I always like VHO also. But anyways this new thing were these so called power compacts...please school me on these...are they HO or VHO or where do they fall in real lighting terms.  They were two tubes with a glass jumper at the far end making it essentially one continuos tube and a single oval base...and one electrode per side at the base.  Here's a picture.  I remember her replacing two 175 watt halides with 4 96 watt 30 something inch tubes and they worked well...but I ways prefer the point source glimmer and water ripples of halides but never could afford. These have always been a mystery lamp to me… Were they used in something other than aquarium for high lightnrequiring photosynthetic corals or were they specifically developed for this? Thanks 1 million guys, this will finally answer a a long mystery i always keep forgetting to ask and just thought of… Here is a picture of a hood  look with them! I believe now LEDs are taking over… That and plasma lamps which have me puzzled if anyone can explain that too I would appreciate… Tictac sized lamps that are called plasma lamps… I would guess they are a form of each HID? Don't mean to side track as these "Power Compacts" as they were called are my main mystery I would like to know about! :-). Thanks a million!

http://www.aquamarinegoods.com/images/power%20compact%20light.jpg

most are just n.o pl-l with special phosphor mixes.some are overdriven.
some even made for reptiles.
a few have one type of phosphor on one side and a different one on the other.
i still prefer the common t12 tubes.i have always bought them on closeout sale when the stores change suppliers.no power compacts showing up like that as they are often special order and expensive.

Oh wow I never knew these were in a class of there own called PLL fluorescents!  So I googled PLL and am finding bits and pieces, no wiki articles or whatnot,  so are they basically a normal output tube of its own custom thickness (not T5,T8,orT12) and bent into that shape?  I remember back in early 1990's my first compact fluorescent was a 9 watt one that plugged into a boxy ballast with a screw in base.  So PLL is Phillips specifically?  Very interesting!  We're they used in commercial way before they were tweaked to aquarium required spectrum?  Thanks a ton again. Oh and I stand corrected, they do have 2 pins per tube...not like a neon sign...they have the square arrangement or straight line pin arrangement for the 4 pins at the single base of the tube! Yes I prefer regular old stylel T12 too!  These PLLs were quite delicate!  The lady broke a few snapping them into the far end support...they snapped right in half (the long 96 watters) at that glass junction opposite the base end! And she would be trying to be careful and become quite upset being they are expensive and that's definitely not covered by warranty!

I've seen the PL-L 55w ones used in those parabolic troffers here. Those have four pins arranged in a straight line.