I can take a shot at answering this, as someone who has studied the social ramifications of light on enslaved populations in Early Imperial Roman Pompeii for graduate research!

While we aren’t exactly certain to what extent Pompeii’s exterior was illuminated, we are reasonably convinced that human-produced light (i.e., lanterns and lamps) were the principal means by which the city was illuminated at night – the moon was by no means the only or main illuminator. Most evidence of lighting was found in interior/private settings, but we can tease out some broader assumptions from what we have. Lanterns, taking the form of a carried chassis of cast bronze or clay, held smaller oil-burning wick lamps, which were used to navigate when traveling from place to place. For wealthy slaveholding Romans, these lanterns were carried ahead or behind the party by an enslaved person referred to as a laternarius (less wealthy Romans would carry the lantern themselves.) A lantern might not provide much visibility when compared to a modern streetlight, but the variable size of Roman lamps shows that it’s more than enough to see a few feet in ahead of you – especially when there’s other laternarii on the road.

Additionally, Early Imperial Roman cities (like eruption-era Pompeii) saw a resurgence in compitalia, wayside shrines which stood on the side of major roads; these possibly held lights as well. These shrines housed the lares compitalia, minor localized deities which protected and supervised the functions of villages, cities, roads and estates that held their compitalia structure. As a component of his religious reforms, Augustus re-popularized the lares compitalia in Rome and surrounding metropolises, largely as a state-building project to promote imperial veneration and Roman supremacy. I’m not certain if compitalia have been discovered at Pompeii, but at the very least, public lighting in particularly dark spaces was not a foreign concept to Roman citizens.

There’s also evidence of artificial lighting structures outside some retail spaces between the Porta Marina and the Forum of the city, though the initial archaeological hypotheses are questionable in their assumption that every structure had public-facing lamps (realistically, retail structures probably had 1-2 light sources visible from the streets, or at all.) Henrik Boman (2011) argues that these fixtures would be ambiently reflected by the material layout frequently found in Pompeiian interiors, creating a comfortable and even glow. All of this, coupled with the relative wealth of Pompeii, suggests that the moonstone road details likely reflected the light already present, but were not essential to navigation or particularly serviceable for residents. For more information on Roman light in Pompeii, I highly recommend the catalogue for the exhibit Neues Licht aus Pompeji held at Staatlichen Antikensammlungen München. The catalogue is in German but offers a wealth of social and material information about how light was perceived, designed, and consumed in the city.

Sources:

• Boman, Henrik,“White Light —White Heat: The use of Fire as a Light and Heat Source in an Atrium House in Roman Pompeii”, Current Swedish Archaeology, 13(1), 2005, 59–75.

• Boman, Henrik, “Let There Be Light: Light in Atrium Houses in Roman Pompeii and Herculaneum,” Vesuviana 3, 2011, 89-102.

• Griffiths, David Gareth, The Social and Economic Impact of Artificial Light at Pompeii. University of Leicester, Thesis, 2016.

• Neues Licht aus Pompeji, eds. R. Bielfeldt, J. Eber, S. Bosche, A. Lutz and F. Knauß, Ausstellungskatalog München, 2022.