I know that this may be hard for some of you to answer but this question came to me when I accidently smashed my pink Toshiba F40T10 fluorescent tube.
It could be a special bulb burning out, The cap breaking off the glass envelope, A rare fixture getting replaced with LED, or perhaps the thing that's happened to many of us at least once, accidently dropping or smashing a special or rare light bulb.

For Ria and myself it has to be the loss of 'Thomas' 

I wrote a poem dedicated to him at the time, and I thought it was on the message boards somewhere. 

But here it is again:

Our oldest lamp filled up with smoke
Poor Thomas has gone and broke
There was the sound of a crack
Now we’ll never get him back
At nearly 70 years old
They’re no longer sold

At the time of writing he was our oldest blub but now we've got older ones in our collection. 

Throwing away some of my first bulbs ever.

I found out today that the garage I had to keep all my streetlights in over the winter flooded and then froze. I can't get to them right now, but most of my street light fixtures ended up at least partially underwater so their ballasts are probably ruined. Kind of thinking I'm just going to quit collecting after this, I'm still a bit shocked it happened.

Including the MH 115?

That and the 50w HPS one was high enough up on a shelf it was alright, the rest of them though I don't know.

At least those might be good.

The ballast wires became exposed on my vintage 3 lamp preheat F40T12 light, now I have to replace all of the wires and that's gonna be hard. I also have to replace the capacitor in the ballast as it also went bad. I plan to put 2 of my 1970's vintage rapid start ballasts in it for now as I don't have any other preheat ballasts. It sucks but when I have the time, I am gonna repair the ballast.

When I realised that the optic style of traffic signals can't run the halogen lamps they were designed to use for extended on times, followed by extended off times, as the unit is sealed and thermal expansion cracks the lens.  (on the roads the lamps are either not on long enough, or off long enough for it to be an issue)

When the original refractor on my M-250R2 was totaled by SmashEx years ago.