Chip wrote...
I *think* thinner glass is a way to reduce stresses from heating.
I *think* a bayonet bulb is likely to be subjected to more
mechanical stress when installed and removed. But I don't know how
much the British equivalent of a 100W A19 weights, and I don't know
if all American A19s weigh about 28 grams.

A standard 100w GLS lamp of store's own brand [Safeway, showing how
long we've had it] weighs 30g (+/- 2g accuracy of the electronic
scales).

100W Osram GLS - made in France - is also 30g on my mechanical dietary
scales.

I suspect that ES lamps are likely to be subjected to more stress on
installation than BC. Not because they need to be but because most people
will screw them down tightly (in the same way thet they over tighten their
taps (AKA faucets) when turning off - to the ruination of tap washers).
Stress on a BC lamp is limited by the contact spring pressure and there is
no temptation to apply any more force once you have rotated the couple of
degrees necessary to engage the pins.

David