The light level the authors used was 20 times lower than that produced by a streetlight, showing that even small changes can have an impact on animal development.
Abstract: Nature v494, pp 284–285 (21 February 2013). <doi:10.1038/494284d>
Original article: Dominoni, D, M Quetting, and J Partecke. 2013. Artificial light at night advances avian reproductive physiology. Proceedings Royal Society B v280, n1756, pp20123017. <doi: 10.1098/rspb.2012.3017>