I follow the guideline that you replace your Reptisun 10.0 tube every 6 months. I use a sharpie and write the date on the tube when I put it in service so I know how old they are. That being said, when I do a change, the tubes are still making light, it's just that we don't really know how much UVB they are still putting out. Can those tubes that I take out of service be used for lighting? I have several under cabinet lights and work lights that use tubes that size and it seems wasteful to throw out a working tube. I don't spend a whole lot of time in those areas, so it's not like I should be exposing myself to harmful amounts of UVB , I wouldn't think.
I wouldn't consider it safe to use them. While they usually are not putting out sufficient amounts of UVB after 6 months for a DRAGONS needs, its still putting out a fairly good amount. I would stay safe and just use normal fluorescent and not try to recycle a use out of the reptisuns.