The paper (which is very short) said 500-700nm and referenced an older (1997) paper that reported on a bunch of UV and visual emitting living systems. I looked there but didn’t pinpoint an answer. It did mention that the emission doesn’t usually have sharp peaks (as the reason they trade spectral resolution for sensitivity). It seems like the emitting molecules are large, so it’s probably pretty broad.

Anyway… that made me nice and sleepy.