The photocathode defines the detector's spectral sensitivity, and PhotonPix can be ordered with one of four PHOTONIS HiQE cathodes so the response can be matched to your excitation and emission wavelengths. The plot shows the available sensitivity curves: Blue and Aqua for the UV to blue-green region, Green for the central visible band, and Red for extended sensitivity towards the near-infrared. Each variant covers the full ⌀17 mm active area, so the choice of cathode affects only the spectral response — dead time, timing resolution and count-rate capability are unchanged. Dark count rate does scale with the red sensitivity of the cathode, from below 100Hz for Blue and Aqua to below 1000 Hz for Red, so the narrowest cathode that covers your wavelength range gives the best signal-to-background ratio. If your application falls between two curves, we can advise on the best compromise before you order.