We present optical ( U BV RI ) sky brightness measures from 1992 through 2006 .
The data are based on CCD imagery obtained with the CTIO 0.9-m , 1.3-m , and 1.5-m telescopes .
The B - and V -band data are in reasonable agreement with measurements previously made at Mauna Kea , though on the basis of a small number of images per year there are discrepancies for the years 1992 through 1994 .
Our CCD-based data are not significantly different than values obtained at Cerro Paranal .
We find that the yearly averages of V -band sky brightness are best correlated with the 10.7-cm solar flux taken 5 days prior to the sky brightness measures .
This implies an average speed of 350 km s ^ { -1 } for the solar wind .
While we can measure an enhancement of the night sky levels over La Serena 10 degrees above the horizon , at elevation angles above 45 degrees we find no evidence that the night sky brightness at Cerro Tololo is affected by artificial light of nearby towns and cities .