. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 352 S. M. LINDSAY ET AL. 490 nm light were used at the following irradiance levels (in units of photons irT2s~'): >: 10", x 10", X 10", X 1012, X 1013, X 1013. x 1013, x 1013, x 1013. X 1013, X 1013. Spectral sensitivity: To measure the spectral efficiency of luminescent countershading. dark-adapted animals were first exposed to a 490-nm stimulus (at X 1013 photons m~2 s~') for 25 min to induce counterillumination. Animals were then exposed to ligh
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 352 S. M. LINDSAY ET AL. 490 nm light were used at the following irradiance levels (in units of photons irT2s~'): >: 10", x 10", X 10", X 1012, X 1013, X 1013. x 1013, x 1013, x 1013. X 1013, X 1013. Spectral sensitivity: To measure the spectral efficiency of luminescent countershading. dark-adapted animals were first exposed to a 490-nm stimulus (at X 1013 photons m~2 s~') for 25 min to induce counterillumination. Animals were then exposed to light stimuli at 20-nm increments from 400 to 640 nm. following the general protocol described above: 60 s darkness, 60 s test wavelength stimulus, 60 s darkness, 5 or 10 min of the standard illumination to main- tain the induced countershading state. This process was repeated for each wavelength tested. The average duration of a complete trial was 3 h. The order of test wavelengths was randomized. Because shrimp eyes operate as photon counters, and the total number of photons in a given stim- ulus is a function of both light intensity and wavelength, stimulus irradiance was adjusted at each wavelength using neutral density filters to obtain equal photon irradiance levels at each wavelength. Even so, there were slight vari- ations in stimulus irradiance levels, which ranged from X 1013 photons nT2s~' at 400 nm to X 1013 photons irT2s~' at 620 nm. Bioluminescence data were subsequently corrected as detailed below to reflect a stan- dard irradiance of X 10 photons m Mean bioluminescence was based on the last 20 s of each 60-s test stimulus, and the last 4 min for the standard 5-10-min illumination. Data correction. Because the test stimuli in the spectral sensitivity experiments varied slightly in intensity, all data were corrected to reflect the intensity of bioluminescence at each wavelength based on a stimulus irradiance of X 10° photons m"2 s~'. Data col
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