Methods2.1.1. ParticipantsParticipants were recruited through the subject pool of Univer-sity College London (UCL). The study was approved by the UCLEthics Committee and all participants provided written informedconsent prior to the study. Payment was £8/h. Using the back-ground survey, for each participant, we translated the reportedmetabolic rate into ‘met’ values as given in Annex B of Ref. [39],separately for each of the four time periods enquired about (‘lastten minutes’, ‘between 20 and 10 min ago’, ‘between 30 and 20 minago’, ‘between 60 and 30 min ago’). The values were then aver-aged across the four time periods. The items of clothing participantsreported wearing were translated into a total score of ‘clo’ (clothing)level as defined in Appendix C of Ref. [39]. Each item was translatedinto its corresponding insulation value and those values were thensummed up for each person. We calculated the Body-Mass-Indexusing the standard formula (e.g. Ref. [21]).Of the 32 participants, 18 were male and 14 female; their distri-bution over the two light conditions was the same (nine males andseven females in each condition). Table 1 summarises participants’characteristics.For the BMI, the difference was almost significant, t(30) = −1.84,p = .08. Hence, this variable was retained as a covariate in subse-quent analysis.