Its body is mostly solid black, with the exception of white discoloration around its pectoral fins and a lateral line of reflective scales.

It is most notable for the bioluminescent organs located underneath its eyes, which it uses to find prey, evade predators, and communicate with other members of its species.

Another difference is that the white spot at the upper corner of the opercle in P. palpebratum is smaller and less drastically colored in P. steinitzi, and is sometimes not present at all.

"[5] As one of the more derived members of Anomalopidae, the flashlight fish shares several synapomorphies with P. palpebratum, Krytophaneron, and Phthanophaneron, including smaller and more numerous scales.

With a latitudinal range between 21°S and 45°N, it has been collected from various islands, including Réunion and Comoros, to as far east as Maldives, as well as north to Somalia, Oman, Israel, and Egypt.

Although it has been observed to share these caves with soldierfish (Myripristinae) and squirrelfish (Holocentrinae), it displays territorial aggression towards other members of its species.

It was initially listed as Data Deficient by the IUCN, but its status was changed to Least Concern in 2020 after an evaluation found wide geographic distribution and no major threats to its survival.