LT Telescope and IO:O Throughput

We measure the absolute photon efficiency of the Liverpool Telescope using observations of photometric standard stars and a throughput model of the IO:O instrument. Over a period of one year following mirror re-coating the telescope transmission is in the range 73--79% over 4000-10000 Angstroms. Transmission in the u'-band (~3500 Angstroms) is slightly lower at 65%. Immediately following mirror re-coating the throughput is shown to be consistent within 4% to predictions for two reflections from bare-aluminium-coated optics. The telescope throughput (two reflections) degrades at a rate ~0.0002 mag/day. Also presented are the effective wavelengths and widths for the u',g',r',i',z',B,V broad-band filters, taking into account all optical components of the system.