Figure 1
Luminette light glasses [Lucimed, Villers-le-Bouillet, Belgium; (A)] and short-wavelength filter glasses [MelaMedic, Viborg, Denmark; (B)].
Table 1
Mean ± SD (range) diary-derived sleep timing variables, on week days and weekends.
| WEEK DAYS | WEEKENDS | |
|---|---|---|
| Bed time (clock time) | 23:36 ± 01:00 (21:42–02:42) | 00:18 ± 00:48 (22:00–01:30) °°° |
| Sleep onset latency (min) | 13 ± 10 (1–48) | 11 ± 7 (1–35) °°° |
| Sleep onset time (clock time) | 00:18 ± 00:54 (22:30–03:12) | 00:48 ± 00:48 (22:30–02:12) °°° |
| Awakenings (n) | 0.6 ± 0.5 (0.0–2.0) | 0.6 ± 0.7 (0.0–2.7) |
| Time spent awake (min) | 12 ± 19 (1–110) | 12 ± 11 (2–45) |
| Wake up time (clock time) | 07:12 ± 00:36 (05:54–08:42) | 08:00 ± 01:06 (03:30–10:18) °° |
| Get up time (clock time) | 07:36 ± 00:42 (06:36–09:42) | 08:36 ± 00:54 (06:24–10:36) °°° |
| Difference wake-get up time (min) | 22 ± 18 (2–91) | 38 ± 35 (0–178) °°° |
| Sleep duration (h) | 6.9 ± 0.1 (4.1–8.1) | 7.2 ± 0.1 (5.0–8.9) § |
| Subjective sleep quality (1–10) | 6.2 ± 1.2 (4.0–9.0) | 6.2 ± 1.3 (3.3–9.0) |
| *Naps (n) | 0.5 ± 0.5 (0.0–1.0) | 0.3 ± 0.4 (0.0–1.0) |
| *Nap onset time (clock time) | 15:42 ± 01:36 (14:12–20:00) | 14:06 ± 02:18 (07:48–16:54) |
| *Nap offset time (clock time) | 16:36 ± 01:48 (14:42–21:18) | 15:00 ± 02:30 (08:24–18:12) |
| *Nap length (min) | 50 ± 28 (15–105) | 46 ± 37 (10–115) ° |
[i] * n = 20 for week days and n = 11 for weekends.
Significance of the difference between week days and weekends: § 0.05 < p < 0.1 (trend), ° p < 0.05, °° p < 0.01, °°° p < 0.001.
Note: Significance levels remained unchanged or improved when analyses were repeated having removed the student with recent intercontinental travel, whose diaries are also responsible for most of the extremes observed in the ranges.
Figure 2
Diary-derived sleep onset time on week days (A; p = 0.4, n.s.) and midsleep on free days (B; p = 0.0022; * p = 0.008 on post-hoc analysis) by Horne–Östberg class, with MM meaning definitely morning, M moderately morning, I intermediate, E moderately evening, and EE definitely evening.
Figure 3
48-hour actigraphy plots of four students [student 1: female, 23 yrs, moderately morning, Pittsburgh Sleep quality Index (PSQI) normal, Epworth Sleepiness Scale (ESS) normal; student 2: female, 24 yrs, intermediate, PSQI abnormal, ESS normal; student 3: female, yrs, intermediate, PSQI normal, ESS normal; student 4: female, yrs, intermediate, PSQI normal, ESS normal] marked alternatively in grey and white. Sleep onset times from the corresponding sleep diary are marked as blues asterisks, wake up times as red circles, and naps as green lines. The two black circles mark a night awakening in Student 1 and a slightly disturbed sleep onset in Student 3.
Figure 4
Proximal skin temperature over time (from 22:00 to 06:00 hours) in a 22-year old female student (A) and a 23-year old female student (B) whose sleep onset timing on that day (broken vertical line) was 01:35 and 23:30, respectively. In both instances, declared sleep onset timing immediately preceded/accompanied a dip in proximal temperature. The sudden and large decrease in temperature in plot B at around 05:30 was most likely due to displacement of one of the three sensors.
Figure 5
Diary-derived sleep onset latency, in minutes, prior to and during the course of chronotherapy (p < 0.05), adjusted for time of the week.
Figure 6
Bed time, sleep onset time, wake up time and get up time over the course of 14 days in the 23-year old female student who had recently returned from Asia. The commencement of chronotherapy (broken vertical line) seemed to regularize her sleep-wake timing. Saturdays and Sundays are marked on the x axis.