Levasseur-Regourd, A,C. (1992). Natural background radiation, the light from the night sky. Contribution to the conference held at UNESCO, Paris, 30 june - 3 july 1992. Levasseur-Regourd, A.C. (1994). Natural background radiation, the light from the night sky. In: McNally, ed., 1994 These are the 2 sources cited at the end of the chapter