What is the minimum amount of light that must enter a living space?

As for the amout of light that is required it is not regulated however every municipal jurisdiction that regulates building construction has a regulation regarding the amount of window space each living unit must have. In most areas it is 10% of the floor space of that unit, however this may vary depending upon the regulations.Window space can be measured and regulated. Light may possibly be measured but it is impossible to regulate it. Hope this helps. Bob the builder.