Just one incubator. What Size Light?

I know what I am using now for my clones and it works well. I took a few flouro tubes and they are doing me just fine. I want to get some Christmas presents ready for a few friends and was wondering what size CFL you would use for a single incubator dome and tray full of clones to grow them nice and strong and healthy. I want to do as little as possible and get as little as possible because this setup will only be for about amonth, but it is really important to have healthy strong clones without overkill by providing more lumans than they can use or need. So if you had to choose what size cfl would you go with? Aftwerwards I'll just use the cfls to replace some of my incandesent bulbs.