In uk.d-i-y WM wrote:
Here in the UK, at my local Tesco supermarket I saw some GLS bulbs
which has a glass envelope that were slightly smaller than usual.

What's the idea behind this?

Wouldn't a 100W filament make a smaller bulb glass envelope get
hotter than the larger standard envelope.

And therefore wouldn't this make the life shorter?

No.
You simply increase the filliment thermal conductivity to the outside,
by various means - usually the problem is isolating it from the
environment - making the filliment cooler is easy.

I don't know exactly what this will do to efficiency, it's horribly
complex.