Visible
In the visible, the natural sky background is dominated by the light diffusion, with some emission lines, esp. toward the red end of the spectrum ( R and I bands).
sigma-clipping method to reject the astronomical objects. Results for zenithal surface brightnesses are listed in Table 3. It shows that La Silla has an excellent sky in terms of darkness.
The sky brightness was measured on all the moonless archive images of the SuSI-2 instrument with exposure time longer than 200s. The background was estimated using an iterative