I thought they were going to stop selling T12s a long time ago, but both bulbs and fixtures are still widely available around here.
Lamps of a higher color temperature appear brighter, because they render colors better--so light doesn't seem as "dim". What we call "daylight" can range between 5,000 and 6,500 degrees kelvin... You may see "cool white" or "daylight" used on lamps that fall into this spectrum. While they do provide better color rendering and may appear to be brighter, they can also mess with your circadian rythym if you are in an area lit by them for a while. That is, your body isn't used to seeing "daylight" for unnatural periods of time, and you end up with headaches, fatigue, etc. Most places (especially office buildlings, etc. where people stay for a long time) use the 4100k ones, while you might find 6000k in a paint store.
