A thermal activation energy of 1.5 eV for the activation of rhodopsin is needed to reduce the rate of thermal activations below the rate of optical activation at the luminance of the absolute threshold. The thermal energy of 1.5 eV is not inconsistent with the optical threshold energy of about 1.8 eV.
© 1978 Optical Society of America
N. Ben-Yosef and Albert Rose, "Spectral response of the human eye," J. Opt. Soc. Am. 68, 935-937 (1978)