I can't find the specific wording but my hazy memory of the regs is that for vessels under 20m there is no requirement for you to have your anchor light on when moored in a designated mooring field.

What exactly a 'Designated mooring field' is, I recall is open to interpretation in different parts of the world.

Regulations aside...having your anchor light, or a cockpit light on can only assist you in not getting hit by rum-filled hooligans in dinghys...or even staff shuttles returning to Tortola from places like Norman Island late at night.

Our experience is that around 75% of boats in mooring fields in the BVI have their light on when on a ball...but i'd also add that a fair few of those seem to turn it on at the start of their charter and off again at the end of the week!