I like to have at least three replacements for each fixture, with some exceptions.

There's an F8T5 nightlight in our bathroom that I found a bunch of replacements for, so that lamp can be replaced about 25 times.
I found a great deal on F17T8s, so I have a 30pk case for a F17T8 lamp displaying a few boxes of computer mice
I have a 3x40W PL desk lamp that I only have three replacements for

I have a lifetime supply of F40T12's, F32T8's, & F20T12's .. I'll go EOL long before there'd be any chance of using them all up (even if I was to run my lights 24/7 I'd still be fine)
The only thing I'd like to get a couple more of are certain colors of F54T5. (if I'm going to do it, need to do it before the end of the year when the bulb-ban kicks in) Prices on eBay are too high anymore, so I'll have to look elsewhere.

We've got a big box of lampses for the general purpose lights in our flat that will outlast us. 

It depends of the lamp. With incandescent lamps that are mostly used around the house I originally had about 10 lamps of each shape and purpose. But as time goas by I get more when I find them for free  in the lamp recycling box because why not, some times I find rare ones too, at least I save them from going to the lamp recycling factory which will crush them to get the different types of metals in them.  

That's only if it's financially worth their while to do it, otherwise they'll end up in landfill. 

Too many!  , I’d probably have a life time supply of all lamp types if they were just for use in the house!

The way things are going with the phase outs…. As many as physically possible!!!!

We're already at the saturation point with lampses.!

Too many. And I'm a dingus and keep grabbing more. I burn through incans the most so I just collect a steady flow of whatever modern stuff I can find at restores/dollar stores. I prefer the behavior/color/CRI of incans for some types of lighting (bedrooms, bathrooms kitchens). I also like to use high wattage (300 watt) in attics and closets. Since they receive little use. Why not. I use CFLs in some spots mostly for nostalgia reasons and have a small stockage of spares for that. I don't stock many LEDs unless they're unique. No point since I can just get them from the store.

I got a bunch of random mercury lamps that will probably last me forever. I got a bunch of halides. And HPS. I need to get a case of 100, 150 and 70 watt HPS. I have yet to find any. It's honestly a lot easier to find mercury lamps than it is to find HPS. Which is kind of annoying sometimes considering how common HPS is.


Linear fluorescent is a nightmare. I have a lot of them. And having to move them around is annoying. But without them I wouldn't be able to keep my stuff running. I actually need a case of F40T12 and F32T8. I have a bunch of randoms but about 80 percent of them are used. I don't really care about brand or color as long as they aren't watt savers or complete junk. I have yet to just find a full case of F40s or F32s laying around.

Lots...mainly HIDs of any type. I have enough to outlast probably three generations of humans! 

 I don't keep too many replacements for stuff around the house . With the life ratings of decent HID , 3 spares should last 15-20 yrs. running D2D ! I don't keep any for the readily available lamps  .