Full of Amusement.......In a difficult human way a lot is being learned here......
There are not many koi keepers here on Bito who have to deal with winter extreme........AND I don't know the EXACT science of why koi can make it through the winter....WITH OR WITHOUT sunlight......But my koi do ALL RIGHT (I would prefer to live in Hawaii
)....AND I STILL have my first koi going on 15 years (maybe 16) here in Michigan. During my koi keeping years I have lost several during the winter, but have seen total loss before by other pondkeeps.
The biggest factor for frozen ponds is oxygen ESPECIALLY if your pond is overstocked. Once that ice covers the entire pond and there is no OXYGEN you are flirting with dangerous waters. Which I think is obvious to everyone?
The sad experience I have had with light is when I have had to bring weaker koi in my house FOR THEIR SURVIVAL.....When that happens color can fade....This past winter I had to bring in a 14" Ginrin kohaku back in early Febuary...The color was a strong orange/red....Now most of the color has faded except for the head..I must admit the tank I use for WINTER EMERGENCY is small, which could affect as well......Well at least it's still breathing.
May the force be with you!!! Or the Darkside if it works better for you....LOL.