Transmittance
We measured the transmittance of our samples with a spectroscopic transmittometer and turned to the Filmetrics F20 UV in the CMi at EPFL. We performed the measurement over the range from 200nm to 1100nm, and then focused on the value obtained at 460nm (see Fig. 1). This is the wavelength that will result in the opening of the light-sensitive ion channels present in the neurons of the transfected mice used in our experiments.