Osram have given their standard H4 bulbs a 250/400 hour B3 rating (B3 the length of time that 97% of bulbs last - the two numbers are for each filament). For the Nightbreakers, they give it a 80/200h B3 rating, so half the lifespan, possibly less.
They do come out top in most of the reviews for bulbs though, so you have to weight up the benefit against the lesser lifespan.
"Y mae dafad ddu ym mhob praidd"
1972 4/4, 1981 MGBGT, 1984 FLHT1340, 1980 XLH1000, 1990 ZX10
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