Rio 180 Lighting Question

[Andeekaii]

I've just purchased a Rio 180, but i've noticed it has 45W/895mm T5 tubes?!
On my current 3ft tank i have a Sylvania Grolux 39W/850mm Tube, and a Phillips 39W/850mm.
I wanted to get the same lights for my rio but I can't get them in that size on lampspecs. After further reading it seems juwel use a custom size. Great.

My question is: Can i use the 39W bulbs on the Rio 180 45W light unit?

Otherwise i'm going to have to DIY some kind of mount and put my original 39w tubes and 39w starter in.

Thanks, Andy