 different observation conditions: Dark conditions with nominal HV (black), 0-0 $\times  \textit{NSB}_{\text{Dark}}$ with nominal HV (blue), 0-0 $\times  \, \textit{NSB}_{\text{Dark}}$ with reduced HV (green) and 0-00 $\times  \textit{NSB}_{\text{Dark}}$ with UV-pass filters (red). 