New spotlight bar accepts two cables, but existing florescent bar light contains 6

Yes, the three cables currently at the light are the feed in, feed out, and switch line. You probably will see all the reds together in a connector block. This is how it needs to stay. Then in the N of the old fitting will be two blacks/blue, and in the L will be a black (should be sleeved or overlapped red/brown) or a brown. You need to take the florescent down keeping a note of what is the N and L, then just put new fitting up, the reds still all in a connector, the earths in the earth terminal the two blacks in the N terminal and the sleeved black into the L terminal. Hope this helps

Hi you have three pairs of (fat) cables coming into the fitting both have red/brown and black/blue. One comes from the supply which will be red/brown = live and black/blue = neutral – One goes on to the next light which will be red/brown = live and black/blue = neutral – One will come from the light switch the red/brown is live to the switch and the black/blue is live return from the switch (which should have some red/brown tape/sleeving on it letting you know its live) so when the switch makes the live returns up the black/blue cable which makes the light work. Therefore the three reds are common and are connected together two blacks/blues go to the neutral and one black/blue goes to the live. The trick is identifying the switch wire, if it hasn't got any tape/sleeve on it it might be turned over on the end. If you haven't taken it apart yet mark the black/blue cable on its own that will be the switch live connect that to live. All of the remaining black/blues connect in the neutral. All of the reds are common and get connected together not to the fitting. Hope this helps you get your head around it. :)