I suppose there is a point to testing the extended envelope of the IFR configuration.
It must be remembered though that many of the 412 aircraft (and others) leave their night suns on permantely thus flying all airpspeeds and profiles by day and night.
Detrement in climb gradients would be the same, the aircraft and night sun don't know if its dark or not.
There are aircraft configurations out there that have Climb Detrements attributed to the aircraft because of external equipment fitted without the extended flight testing.
At the end of the day it comes down to the wording; "IFR operation is prohibited with Nightsun
Searchlight
installed."
The bigger factor to this is the following scenerio;
Crew receive callout which is an IFR flight, they install Night Sun to aircraft planning to fly enroute IFR and then when visual use the night sun for the landing phase. Pretty normal, would you say.
Q: What would happen if there was an incident? - Would the insurance company still pay up?
Food for thought!