The finding that with a reasonable effort a layer thickness and/or refractive index variation may be acquired which realizes different internal optical path lengths for impinging radiation whereby fluctuation of spectral sensitivity of the photodetector is reduced is used to provide image sensors with a less fluctuating spectral sensitivity with respect to different wavelengths, or photodetectors with a small fluctuation of the spectral sensitivity from photodetector to photodetector with respect to defined wavelengths, with a reasonable effort.