Everyone agrees that the regulations require the lights to be on during night time.
For the regulations, the start and end of night time at the aircraft position is determined at the surface. It also varies from country to country and at times of the year.....one country says 30 min after sunset until 30 min before sunrise, another says sunset to sunrise while yet another uses the first definition during the summer and the second one during the winter.
I have a distant memory of calculating the position of the aircraft at sunrise during a navigation exam but have never used the principle since.
So, for those who leave the lights off by day, when exactly do you turn on the lights and if it is when the sun sets at 35,000ft, isn't this after legal sunset (at the surface)?
Regards,
DFC