Wouldn't the rooms inside need more lighting then? I wonder about where the break even point is on those differences. I'm not educated in this area enough to even guess.
I assume they mean on the bits that don't have windows. Though caution would be required there; you have to be very careful about tall building cladding material (see https://en.wikipedia.org/wiki/Grenfell_Tower_fire).
Lighting, incidentally, is practically _free_ these days. An EU 'A' rated LED bulb has to do 210 lumens per watt. So the equiv of an old-fashioned 100W incandescent uses 7.5W.
