Measurements of light at night (LAN) for a sample of female school teachers
Authors: Jennifer A Brons
Mariana G Figueiro
Mark S Rea
Journal: Chronobiology International (2011)
Discipline: BIOLOGY & BIOCHEMISTRY
Keywords: Rotating shiftwork; Breast cancer; Light at night; Satellite photometry; Bedroom brightness
Affiliations: Lighting Research Center, Rensselaer Polytechnic Institute, Troy, New York 12180, USA. 

Abstract:  Epidemiological studies have shown an association between rotating shiftwork and breast cancer (BC) risk. Recently, light at night (LAN) measured by satellite photometry and by self-reports of bedroom brightness has been shown to be associated with BC risk, irrespective of shiftwork history. Importance has been placed on these associations because retinal light exposures at night can suppress the hormone melatonin and/or disrupt circadian entrainment to the local 24-h light-dark cycle. The present study examined whether it was valid to use satellite photometry and self-reports of brightness to characterize light, as it might stimulate the circadian system and thereby affect BC incidence. Calibrated photometric measurements were made at the bedroom windows and in the bedrooms of a sample of female school teachers, who worked regular dayshifts and lived in a variety of satellite-measured sky brightness categories. The light levels at both locations were usually very low and were independent of the amount of satellite-measured light. Calibrated photometric measurements were also obtained at the corneas of these female school teachers together with calibrated accelerometer measurements for seven consecutive days and evenings. Based upon these personal light exposure and activity measurements, the female teachers who participated in this study did not have disrupted light-dark cycles like those associated with rotating shiftworkers who do exhibit a higher risk for BC. Rather, this sample of female school teachers had 24-h light-dark and activity-rest patterns very much like those experienced by dayshift nurses examined in an earlier study who are not at an elevated risk of BC. No relationship was found between the amount of satellite-measured light levels and the 24-h light-dark patterns these women experienced. It was concluded from the present study that satellite photometry is unrelated to personal light exposures as they might affect melatonin suppression and/or circadian disruption. More generally, photometric devices calibrated in terms of the operational characteristics of the human circadian system must be used to meaningfully link LAN and BC incidence. 

Retracted: No

PubPeer comments:
 Readers should be aware that this article was further discussed in four additional pieces also published by Chronobiology International. The first two were published together in the same issue as the original article itself. The first was a  research article written by Richard Stevens: https: doi.org 10.3109 07420528.2011.606945, the second was a  letter to the editor written by Abraham Haim and Boris Portnov: https: doi.org 10.3109 07420528.2011.604591 The third piece was published in a later issue, a  letter to the editor written by Christopher Kyba and Franz Hu00f6lker: https: doi.org 10.3109 07420528.2011.630294 The same issue in which the third piece was published also included a  reply to letter to the editor , by Mark Rea, Jennifer Brons, and Mariana Figueiro (the original paper s authors): https: doi.org 10.3109 07420528.2012.630569 ,