Also I am sure that if you have the 54w juwel 1200mm unit you could solder some extra length onto the pins and make a standard 54w t5 tube fit. Its only really the wattage that counts with these things.
There are 3 or 4 manufacturers or Juwel length tubes, Juwel, Arcadia, Geiselman and iQuatics.
The reason they are custom lengths is due to the limited tank volumes you would get using industry standard length tubes, especially in smaller volumes under 300-400 litre. All to do with ratio of width to "pleasing" depth, for industry standard lengths give nothing in 100 litre to 300, litre range. Juwel have, 80l, 125l, 180l, 240l, 260l, 350l. These volumes are possible using standard tubes but tanks, in the above volume range, would look "unpleasingly" shallow. I did post about this, years ago after getting an email (2000' odd) from Juwel why they made their own length tubes.
I am trying to find out who that manufacturer is? I know some other manufacturers make juwel length tubes. But iQuatics are the only ones I can easily find and they are of lower quality. Geiselman I would be interested in. Truth be told I'M a reef keeper and interested in mairne spec tubes.
What do you mean lower quality ? My iQuatics tubes are from Jan 2016 and are still fine. I know this as I recently had a Juwel tube fail, so I played "musical tubes" and there was virtually no difference in brightness between the old tubes and brand new unused tubes.