Fig 4. Variation of nocturnal light intensity as a function of cloud cover and baseline level of artificial lighting.
The effect of cloud cover is estimated as the ratio of nocturnal irradiances (clear overcast sky over clear sky) against the baseline irradiance of a nocturnal clear sky during the new moon. (left) untransformed data, (right) log-log transformation. The line represents the model of linear regression (r2 = 0.612).