Mean data from Table 2 of Baylor, Nunn & Schnapf (1984). n, the number of records averaged together, varies from 5 to 10 depending on wavelength.
Cynomolgus monkey (Macaca Fascicularis).
Suction electrode (current) recordings made with a light beam passing transversely through rod outer segments.
The λmax value is ~491 nm.
Baylor, D. A., Nunn, B. J., & Schnapf, J. L. (1984). The photocurrent, noise and spectral sensitivity of rods of the monkey Macaca fascicularis. Journal of Physiology, 357, 575-607.