Fireflybob, when I was last involved with RAF teaching (2003) it was and I doubt it will have changed., conspicuity being the overriding consideration. Also no mucking about with switches etc. on the runway, so all checks done while stationary, brakes on, before takeoff or clear of the runway after landing. Less scope for errors and being head-down while moving on the ground.
Ryan5252, apologies, I stand corrected then, although I am talking here about being dazzled i.e. vision adversely affected, not just noticing a flash in my peripheral vision. I have been dazzled by airliner taxi/ landing lights at night, but never by light aircraft in daylight. But then I never need to wear sunglasses either so you are probably right, it's variable.