Period Sky brightness (mag/arcsec²) Annual increase (%) Cause References Pristine Mt. Graham, AZ, USA 2000 – 2008 21.5 – 21.8 0 solar activity Pedani 2009 Hawaii, USA 1986 – 1996 21.3 – 21.9 0 solar activity Krisciunas 1997 Cerro Tololo/Chile 1992 – 2006 22.0 – 21.2 0 solar activity Krisciunas et al. 2007 Kitt Peak/Mt. Hopkins, AZ, USA 1988 – 1999 Δ 0.1 – 0.2 1 – 2 ordinances Massey and Foltz 2000             Urban Flagstaff, AZ 1974 – 1982 Δ 0.4 5 Lockwood et al. 1990 IAO, India 2003 – 2007 21.3 – 21.1 5 Stalin et al. 2008 Mt. Wilson, USA 1973 – 1999 19.8 – 18.8 3.6 city lights Los Angeles Teare 2000 1900 – 2000 Δ 2.7 2.5 city lights Los Angeles Garstang 2004 Mt. Hamilton, CA, USA 1950 – 1975 21.9 – 20.6 5 city lights Walker 1973 Ekar, Asiago, Italy 1960 – 1995 21.6 – 20.2 10 city lights Cinzano 2000 G. Haro, Mexico 1994 – 1997 20.5 – 20.0 19 city lights Carrasco et al. 1998 NAO, Japan 1958/1978/1989 20.5/19.5/17.6 5 – 17 city lights Tokyo Isobe and Kosai 1998             Worldwide Expert guess 3 Narisada and Schreuder 2004             Indirect (energy consumption) UK Campaign to Protect Rural England (CPRE) 1993 – 2000 4 DMSP data CPRE 2003 UK McNeill 1984 – 1999 1.86x lmh 4.2 street light McNeill 1999 UK Fouquet/Pearson 1950 – 2000 5x lmh 3.3 overall energy consumption for light Fouquet and Pearson 2006 USA 1967 – 1970 20 energy + efficiency Riegel 1973 France 1990 – 2000 3 energy ADEME 2007 Germany 1950 – 1990 8 energy + efficiency Hänel 2001

Note: IAO India = Indian Astronomical Observatory, NAO Japan = National Astronomical Observatory of Japan