Purpose: Direct measurement of the transmission of light through the human lens is not possible in vivo unless invasive techniques are used. In the current study, a reliable in vivo estimate of the transmission of blue light through the lens was assessed by comparing an indirect and noninvasive method based on autofluorescence measurements with a direct method. Methods: Total transmission of blue light was measured in human donor lenses using a direct method applicable only in vitro and compared with transmittance estimates made by an in vivo applicable autofluorescence technique. Results: Human lens transmission of blue light decreases with age by 0.7-0.8% per year at 480 nm. The comparison of methods showed that the autofluorescence-based method correlated significantly with the direct measurements (R = 0.83, p <0.001) and acceptable agreement between the two methods was found. Discussion: In conclusion, the human lens transmittance of blue light can be measured reliably in vivo. This enables the possibility to correct for retinal light intensities when studying the mechanisms of the circadian rhythm in clinical studies and related disorders and in addition when working with clinical and experimental methods affected by retinal blue light intensities.