This question is mainly for those of you who maintain fluorescent luminaires, but others feel free to post if you wish.

I maintain a small number (3 to date, more to come) fluorescent night lights. They are in a windowless room in a church basement, and each uses one F15T8 tube. They run 24/7. This past July, one tube went eol, and while changing it, I decided to date it, so that when it fails, I would know how long it lasted. I carefully marked the date with a Staedtler Lumocolor blue felt marker on the glass, in the centre of the tube. Today, I went into that room and decided to look how the date marking fairs out. It has completely faded ; just as if I never marked it. Do any of you mark your tubes with the installation date, and if so, what do you use ? I thought of using a black grease pencil (China marker or Berol Blaisdell) but had none at hand at the moment. Thanks.

I've just used a sharpie, and it seems to hold up alright.  One tip maybe to mark the endcap instead of the glass.

Mark on the socket, not the glass, the strong light would degrade most marker's ink...
The maintenance guy at my work use regular OHP pen and write directly the date in regular numeric form...

Thanks for the info. I will use a black sharpie on the endcaps next time.

I used a sharpie on the glass part they never wore off.

I used a sharpie on the glass part they never wore off.

I have the experience the light is quite aggressive and the ink not much light stable, that's why the socket area should work a bit better. Moreover the socket is usually not as glossy surface, so bond the ink a bit better...

I recently switched to using an electronic spreadsheet to record relamp dates. Only a lighting collector would spend that kind of time, but it works!

I use a sharpie myself.  I will wipe down the area I mark (usually above or below the brand stamp) with windex or whatever glass cleaner I have on hand, and after it has dried, will date it there, and again on the end cap with a smaller sharpie.  Thus far, I have tubes I replaced as far back as 20 years that still are very much readable on the tube. 

I do it slightly different, I have a little `insallation and relamp` date book.
Each of the 37 lamps in use at home is listed with a changing date in the book, this way you can see which manufacturers lamp types last the longest in what ever job its doing.

I have kept this book since starting it in 1995, and over the years it has some interesting results in!