I'm currently running a Vosla +100 H4 bulb in my motorcycle headlamp. Vosla's data sheet gives B3 and Tc values of 130 and 200 (at 13.2V) respectively for the low beam filament. I've currently got ~195 hours on the low beams at 13.8V so I figure I'm doing pretty well in terms of longevity.

It got me to wondering how the bulb manufacturers arrive at their B3 and Tc values. Do they take a sample set of bulbs and simply keep them on to see how long it takes for 3% and 63% of the bulbs to fail, or do they use computer modeling, or a combination of those?

Also, why 3% and 63% in particular and not, say, 5% and 75%?

Thanks in advance.