Just wanted to report back success here. I did order an EL1499ICA online, although what was shipped was an EL1499ICA-L, noted only on the mfr site as an economy version - but looked dimensionally similar to the original specs. I scheduled to have the electrician do it, less about the electrical than worrying about traversing 20' of attic and accidentally stepping through the ceiling drywall somewhere. Was very simple 10 minutes for the electrician to swap out the entire housing. Before he came, I did look at the housing and there is no way to remove the rectangular sealed box to just replace the transformer - it's basically riveted shut. He was the original electrician from the remodel - said 1 in a 100 of these fails, no good reason... I asked about what happens if one of the downstairs transformers fails, given no attic. He did confirm he could also access from the can itself via the ceiling, as brickeyee said, but it just takes more time and effort that way. I did see that removing three screws allows the can to drop out, although it did seem quite a pain to try to unscrew the old transformer from the housing blind (when your hand and screwdriver have reached into the opening). Would be a very challenging DIY attempt. Replacement housing works great, and learned a few things as a general DIY-er. Thanks, esp brickeyee, for the advice.

One thing that might help with high load-related dimming is a multivolt ballast. I am not sure. They operate on voltages between 120 and 277. It has never been clear to me if they adjust to differing voltages in a discrete or continuous fashion and how fast the adjustment is. Maybe someone else will know that detail. On-off is probably killing your tubes On the other hand, good program-start ballasts are recommended for occupancy sensor use. At some point, you begin to measure fluorescent lamp life in "starts" instead of hours. I wish that I could be more certain that the T8 ballasts will eliminate your noise problem completely. All I can say is that I don't hear mine at all. I know, however, that I have some high frequency hearing loss. Any good new electronic ballast operates above 20kHz for efficiency purposes. They are more likely to cause EMF or RFI problems than audible noise. (They need to be designed to avoid frequencies that cause EMF and RFI problems.) If you buy your ballasts locally, you could just change over one of your three and disconnect the other two for sound testing purposes. If it does not work for you, maybe you can get the store to agree, beforehand, to take the ballasts and lamps back. One thing in your favor is that your lumnaire appears to have non-shunted sockets and is wired for rapid-start/program start. There are some wiring diagrams (and other information that might be of interest) in this link: http://www.lighting.philips.com/pwc_li/us_en/connect/advance/assets/1-01_to_1-69_Atlas2012.pdf I like ballasts that will continue to operate the rest of the lamps if one goes out. Not all do that. I bought two boxes of ten (one each 1 or 2-tube and 3 or 4 tube) on ebay for $10 or less/ballast. I have a lot of linear fluorescent that came with my house and garage. Your light quality is likely to be greatly improved with the T8 tubes. I think that high CRI tubes are available in T12 format, they are not as common as for T8. Look for a high-quality lamp. I bought a bunch of GE SPX tubes. (SP are lower CRI). Other manufacturers have other notations. Color is largely a matter of taste. I like a more natural, daylight color. If you ballasts qualify for the NEMA Premium Ballast program, you are more likely to have good quality. Here is a link that might be useful: NEMA Premium Ballast

davidr - you are correct in that new cans will have a tighter light distribution than the old squares. The reason for the switch is that one of the old squares flickers and spits - so that there is a wiring or fitting problem there. Accordingly I have removed the bulb on that one unit. I thought that if I am going to replace one unit that I might as well replace all of them at the same time or it might not look good. In addition an electrician told me that the old square lights are "dangerous" as they dont have thermal cut-offs and are thus fire hazards....

In both fixtures there is a black, white, and green and then there is a red wire that runs between the 2 original light fixtures themselves. The light fixtures are the old fixtures that will hold just one bulb and they have screws attached to the back that you attach the wires to. We were going to replace the 2 fixtures with the new ones and then run additional lights from there. We were going to use the same cables and just run new cables to the additional lights. Someone told me that we can leave the 2 original fixtures there and just add new wire to one of the lights and wire in the new light doing a "daisy chain" but my husband has now detached all the wires and has no idea how to even attach the two lights back to the way they were originally. Does the red wire normally attach with the black or the white wire?