Recently, I performed experiments to characterise the ultraviolet-A response in a smartphone camera (with the lens still attached). This question focuses on Figure 2 of my paper "Characterization of a Smartphone Camera's Response to Ultraviolet A Radiation" - please note, I am only posting this link to show the figure.
In figure 2, the transmission of UVA through the lens drops significantly at wavelengths of less than about 370nm, not shown in the paper is that several lenses were tested with similar results. However, with the lens in place, UVA radiation from a monochromator at wavelengths as low as 320nm still cause saturation of the silicon-based CMOS image sensor despite the heavy attenuation at wavelengths lower than ~370nm.
What is reason for heavily attenuated UV radiation at 320nm causing as strong response as for far less attenuated UV radiation at 380nm?