Correct me if I’m wrong, but ‘at the exact instant of the new moon ‘ it is broad daylight, isn’t it?
Only in the few days just before and after that moment the effect that Dave mentions occurs.
PS: I just checked some definitions of ‘new moon’ and it seems there is a difference between the popular meaning of the phrase (= when the moon starts becoming visible again) and the astronomers definiton (= when the moon is in conjunction with the sun).
From Wikipedia (via Webster’s online).
Traditionally, the lunar phase new moon begins with the first visible crescent of the Moon, after conjunction with the Sun. This takes place over the western horizon in a brief period between sunset and moonset. Therefore the time and even the day depend on the actual geographical location of the observer.
Currently, the new moon is defined by astronomers to occur at the moment of conjunction in ecliptic longitude with the Sun, when the Moon is invisible and a solar eclipse may occur. This moment is unique and does not depend on location. To avoid confusion with the traditional new moon, this may be called the dark moon.
Edit PPS: just realised that the criterion is that the sun and moon are vertically aligned. To some observers that may happen when the moon is just above the horizon while the sun has just set or hasn’t risen yet.