[See the Page “Ropen Lights seen by a biologist.”]
Cheesman mentioned in her book that “It may be dismissed at once that the flashes were due to any human agency.” She gives a number of reasons for dismissing humans as the cause: It would have required about thirty natives to have coordinated flashing their flashlights, and the lights appeared to be above (not within) the forest. Even if all those natives had climbed trees at night, they would still have been within the tree canopy, not clearly above it. [detailed elaboration by Whitcomb]
She also mentioned that the flash of light lasted for “about four or five seconds.” This is close to the flash-length of the ropen light of Umboi (Siassi) Island, far to the east. It is not, however, close to the indava-light flash that is to the south of Mondo (Mondo is where Cheesman was doing her research, which was on another subject: She was an entomologist).
I noted that she also mentioned that the lights “were showing more or less in a straight line horizontally, and appeared at many points along that line.” Her sighting seems perfectly in harmony with a ropen-light interpretation.