Many popular 4' and 8' fluorescent tubes will no longer be available after July 2012 due to the new standards. Say you have an older fixture with an F34T12/CW tube for example. If it burns out, you'll have three options. One is to install a new ballast that is compatible with a high efficiency T8 tube. This will result in savings but requires the purchase of a new ballast and disposal of the old one, which has an environmental impact as well. Two, purchase a replacement tube compatible with the existing ballast which produces more lumens per watt but costs more and still uses the same amount of energy (such as an F34T12/841 triphosphor tube). Although more efficient, the additional output will probably not be enough to shut off any tubes without changing the layout of your fixtures. A third option is to buy a bulb that is exempt, such as F34T12/CWX because it meets the color rendition standards even though it is actually less efficient. This may be the cheapest option, but in order to account for the lower output, you'll probably need to use the 40W version, which would circumvent the efforts in the 1990s to reduce the wattage of the most common 4' T12 tubes from 40W to 34W.