The MacBook Air 2018 is advertised as 12 hours battery life, the MacBook Pro as 10 hours. This official Apple testing is done using 3/4 brightness setting. Since the maximum brightness of both models differs (300 vs 400 nits). I.e. the testing is at 3/4 * 300=225 nits on the MacBook Air and 3/4 * 500=375 nits on the MacBook Pro.
Which model has better battery life when both screens are set to the same brightness at 250 nits?