It definitely does not apply to restaurant kitchens. For older buildings not at all -- plenty of totally windowless and even basement kitchens -- and even for

It definitely does not apply to restaurant kitchens. For older buildings not at all -- plenty of totally windowless and even basement kitchens -- and even for newer buildings I think "serving station open to the restaurant floor" counts as "natural light" (and actually isn't all that bad). Where I just had lunch they get natural light whenever a waiter opens the door to bring some food out. Source: I live in the EU and have been inside a lot of restaurant kitchens in both Germany and Hungary.