Question: Suppose you see a crescent Moon; how much of the Moon's entire surface (the full globe of the Moon) is in daylight?

The crescent moon corresponds to the illumination in a percentage greater than 0% until before being illuminated at 100%, which corresponds to a phase between new moon and full moon. The moon does not have its own light but reflects the one it receives from the sun. The moon in this phase shows a semicircle that increases progressively, each day the luminous surface increases and thus the reflected light.