How bright is a firefly? Resolving a century of overestimation

A firefly flash contains roughly 108–1011 photons—far fewer than the 1013–1014 photons implied by Coblentz's 1912 report of 1/50–1/400 candlepower for Photinus pyralis. We trace this discrepancy to selective citation of the upper end of Coblentz's range and to systematic biases in early visual photometry. We derive a theoretical bound from luciferase abundance and quantum yield. We also measure flash brightness directly with a lux meter and reanalyze two historical datasets. These independent lines of evidence all fall well below the historical candlepower values. The error persisted because modern bioluminescence research often reports quantum yields and relative intensities; reconstructing absolute photons per flash also requires in vivo substrate turnover or measurement geometry, so the comparison with early photometry was rarely made directly.