Landing Lights Off
A report on the research flying by RAE Bedford (BLEU) - TR 81025 - ‘Economic Cat 3’, suggests that landing lights were not used for any approach. However this was probably due to assessments of different approach and runway lighting configurations and intensity - landing lights off to minimise scientific variability.
The most usable intensities for the runway were a graded change from ‘low’ centreline, ‘medium’ TDZ, and ‘higher’ edge lights; generally both the runway and approach lights set to lower intensities than might be considered.
The report did discuss a small trial involving use of landing lights (possibly without or only with very low intensity runway lights, also with floodlights without runway lights). There were few benefits from these other than at very low altitude when the landing lights enhanced ground texture - for manual landings.
Generally the suggestions were that the reflected dazzle of landing lights was less disturbing than having incorrect, too bright approach and runway lights.
Personal recollection was that landing light dazzle on the approach reduced the height of first contact with the approach lights; and during landing in variable thickness fogs the changing light intensities from the reflections could disturb awareness of the runway lighting pattern. Thus use of landing lights at night could reduce time available for assessing the visual scene - critical decision making, and any benefit during the flare would only apply to pure unaided visual landings (none authorised ?), with potential for distraction in variable fog - blowing snow, etc.
The manufacturer is unlikely to advise - operational issue / approval; thus it depends on the operator or regulator. Requirements vary considerably; those who have considered the research and feedback from other operators, and those who intuitively - erroneously require max approach / runway brightness, and landing lights without considering any negative effects.
Landing lights off.