Try reading the article. For shafts close to the surface they can use fibre optics to bring in sunlight, deeper down they use LED lights.
There is also the point that sunlight is free, and greenhouses already solve the same problems. The Netherlands already does this to great effect: https://www.nationalgeographic.com/magazine/2017/09/holland-...
No idea if this will ever come to fruition, but these people do seem to have done some homework and have prototypes up and running now.
I think most of our disused mines (by area) are deep, and pretty dark places - don't even need to reach pit bottom for total blackness.
Having been down a mine few times not sure I'd want to farm down there!
Surely the real answer is to grow the same foods in commercial greenhouses, heated via geothermal heat pumps and if we're short of land to do this we can always use golf courses for farming!
I really would not like to have to test the UK's government on security of food supply vs love of golf courses. I suspect I already know the answer to that one and it comes in a variety of pastel tones.
Remember reading somewhere that in the UK we use roughly the same amount to land for golf courses as we do for housing.
Of course not all golf courses are suitable for farming but I'm sure there's plenty in Surrey that are!
https://www.ft.com/content/79772697-54e4-32c9-96d7-5c1110270...