TABLE 4.

Daytime sleep and circadian phase markers. Clock time (hh:mm).

	n	7000 K light Mean (SD)	2500 K light Mean (SD)
Daytime sleep
Sleep onset	27	07:45 (0:28)	07:45 (0:32)
Sleep onset latency	27	0:06 (0:06)	0:05 (0:06)
Wake time	27	13:47 (0:57)	13:28 (1:00)
Sleep duration	27	6:01 (0:57)	5:43 (0:58)
Circadian phase
Baseline DLMO	23	21:27 (1:10)	21:30 (1:06)
Final DLMO	18	23:54 (1:23)	23:36 (1:31)
Phase shift (delay)	17	2:43 (1:04)	2:12 (1:14)
Phase angle
Phase angle sleep onset	16	7:36 (1:07)	7:47 (1:27)
Phase angle sleep offset	16	13:37 (2:35)	13:38 (1:55)

Participants with complete data for each variable. Sleep variables derived from averaged actigraphy of the three daytime sleep periods after the night shifts. DLMO, dim-light melatonin onset. Baseline DLMO sampled in the evening one day prior to the first night shift; Final DLMO sampled in the evening on the day after the third night shift. Phase angle calculated as the time interval from final DLMO to sleep onset and offset, derived from actigraphy of the previous daytime sleep period (after the third night shift). There were no significant differences between the light conditions (p > 0.05).