Figure 1
The study setup. The protocol included continuous performance test (CPT), electroencephalogram (EEG), electrocardiogram (ECG), Karolinska Sleepiness Scale (KSS), and visual analogue scale (VAS) for fatigue and sleepiness. EEG, CPT1, and ECG1 indicated that the data acquired during the initial dim period has been used as a baseline for normalization.
Table 1
Photometric values measured at eye level for the 7343 K, 2564 K, and 3730 K light conditions.
| Variable | 7343 K | 3730 K | 2564 K |
|---|---|---|---|
| Color Rendering Index (CRI Ra) | 86.9 | 82.9 | 81.9 |
| Chromaticity coordinates (x,y) 1931 CIE chromaticity coordinates | 0.3023, 0.3117 | 0.3950, 0.3899 | 0.4831, 0.4327 |
| Photopic illuminance (lux) | 333 | 332 | 333 |
| Melanopic lux (α-opic lux) | 342 | 195 | 115 |
| Cyanopic lux (α-opic lux) | 414 | 180 | 73 |
| Chloropic lux (α-opic lux) | 340 | 291 | 259 |
| Rhodopic lux (α-opic lux) | 349 | 236 | 169 |
| Erythropic lux (α-opic lux) | 323 | 319 | 326 |
| Photon density (photons.cm–2.s–1) | 3.14 × 1014 | 2.7 × 1014 | 2.7 × 1014 |
| Irradiance (μW.cm–2) | 117 | 96 | 92 |
Figure 2
Spectral power distribution measured at eye level in the 7343 K, 2564 K, and 3730 K light conditions.
Table 2
Analyses of Variance (ANOVA) results for EEG- alpha, HR, HRV measures, fatigue and sleepiness, and CPT.
| df | Error | F | p | |
|---|---|---|---|---|
| EEG- alpha | ||||
| Light | 2.138 | 44.894 | 28.266 | <.001 |
| Session | 1 | 21 | 3.649 | .070 |
| Trial | 2.797 | 58.74 | 72.806 | <.001 |
| Light × Session | 3 | 63 | 3.949 | .015 |
| Light × Trial | 4.774 | 100.26 | 7.901 | <.001 |
| Session × Trial | 3.115 | 65.419 | .574 | .72 |
| Light × Session × Trial | 5.499 | 115.472 | 1.706 | .132 |
| HR | ||||
| Light | 3 | 63 | 10.256 | <.001 |
| Session | 1 | 21 | 5.507 | .026 |
| Trial | 5 | 105 | .295 | .915 |
| Light × Session | 2.064 | 43.351 | .337 | .723 |
| Light × Trial | 6.626 | 139.153 | .398 | .894 |
| Session × Trial | 5 | 105 | .292 | .916 |
| Light × Session × Trial | 7.337 | 154.078 | 0.633 | .736 |
| LF | ||||
| Light | 2.07 | 43.468 | 7.428 | .002 |
| Session | 1 | 21 | .145 | .707 |
| Trial | 2.133 | 44.802 | 4.792 | .012 |
| Light × Session | 2.043 | 42.908 | .234 | .797 |
| Light × Trial | 6.357 | 133.491 | .768 | .603 |
| Session × Trial | 2.604 | 54.68 | 2.263 | .1 |
| Light × Session × Trial | 5.453 | 114.521 | 1.261 | .283 |
| HF | ||||
| Light | 1.843 | 38.709 | .444 | .629 |
| Session | 1 | 21 | 2.039 | .168 |
| Trial | 2.316 | 48.627 | 9.84 | <.001 |
| Light × Session | 2.216 | 46.531 | .071 | .946 |
| Light × Trial | 3.932 | 82.575 | 1.2 | .317 |
| Session × Trial | 2.264 | 47.553 | .482 | .644 |
| Light × Session × Trial | 5.713 | 119.977 | 1.333 | .25 |
| LF/HF | ||||
| Light | 1.831 | 38.451 | 5.636 | .009 |
| Session | 1 | 21 | .508 | .484 |
| Trial | 2.544 | 53.421 | 2.315 | .096 |
| Light × Session | 1.924 | 40.414 | .542 | .579 |
| Light × Trial | 4.294 | 90.177 | 1.547 | .192 |
| Session × Trial | 2.834 | 59.515 | .975 | .407 |
| Light × Session × Trial | 5.605 | 117.695 | 2.277 | .045 |
| Subjective fatigue | ||||
| Light | 3 | 63 | 12.649 | <.001 |
| Session | 1 | 21 | 16.483 | .001 |
| Trial | 1 | 21 | 45.017 | <.001 |
| Light × Session | 3 | 63 | .547 | .652 |
| Light × Trial | 3 | 63 | 12.045 | <.001 |
| Session × Trial | 1 | 21 | 3.141 | .091 |
| Light × Session × Trial | 3 | 63 | 1.294 | .284 |
| Subjective sleepiness | ||||
| Light | 3 | 63 | 20.632 | <.001 |
| Session | 1 | 21 | 3.012 | .097 |
| Trial | 1 | 21 | 9.991 | .005 |
| Light × Session | 3 | 63 | .2 | .896 |
| Light × Trial | 3 | 63 | 5.552 | .002 |
| Session × Trial | 1 | 21 | 13.975 | .001 |
| Light × Session × Trial | 3 | 63 | 3.451 | .022 |
| CPT mean RT | ||||
| Light | 3 | 63 | 17.282 | <.001 |
| Session | 1 | 21 | 11.26 | .003 |
| Trial | 1.548 | 32.51 | 1.303 | .279 |
| Light × Session | 3 | 63 | 5.185 | .003 |
| Light × Trial | 3.856 | 80.972 | 1.795 | .14 |
| Session × Trial | 2.536 | 53.258 | 1.062 | .365 |
| Light × Session × Trial | 5.2 | 109.201 | 1.577 | .17 |
| CPT accuracy | ||||
| Light | 3 | 63 | .497 | .686 |
| Session | 1 | 21 | 1.072 | .312 |
| Trial | 5 | 105 | 48.146 | <.001 |
| Light × Session | 3 | 63 | .664 | .577 |
| Light × Trial | 7.705 | 161.806 | 2.008 | .051 |
| Session × Trial | 4.482 | 94.126 | 1.192 | .32 |
| Light × Session × Trial | 7.876 | 165.405 | .307 | .961 |
[i] Note. Significant differences (p < .05) are shown in bold.
Table 3
T-test results for EEG-alpha measure, mean RT of CPT, HR, HRV measures, fatigue, and sleepiness during each session.
| Pairs | t | p |
|---|---|---|
| Session 1 | ||
| EEG-alpha | ||
| 7343 K – DL | –5.157 | <.001 |
| 2564 K – DL | –3.670 | .001 |
| CPT reaction time | ||
| 3730 K – DL | –3.229 | .004 |
| 7343 K – DL | –4.053 | .001 |
| 2564 K – DL | –3.817 | .001 |
| HR | ||
| 7343 K – DL | 3.253 | .004 |
| 2564 K – DL | 3.862 | .004 |
| LF/HF | ||
| 2564 K – DL | –3.232 | .004 |
| Subjective fatigue | ||
| 7343 K – DL | –3.893 | .001 |
| 2564 K – DL | –3.792 | .001 |
| Subjective sleepiness | ||
| 7343 K – DL | –5.694 | <.001 |
| 2564 K – DL | –4.557 | <.001 |
| Session 2 | ||
| EEG-alpha | ||
| 3730 K – DL | –3.255 | .004 |
| 7343 K – DL | –8.339 | <.001 |
| 2564 K – DL | –6.485 | <.001 |
| 3730 K – 7343 K | 6.366 | <.001 |
| 3730 K – 2564 K | 4.172 | <.001 |
| CPT mean RT | ||
| 7343 K – DL | –6.014 | <.001 |
| 2564 K – DL | –6.074 | <.001 |
| 7343 K – 3730 K | –3.029 | .006 |
| HR | ||
| 3730 K – DL | 4.372 | <.001 |
| 7343 K – DL | 4.428 | <.001 |
| 2564 K – DL | 3.619 | .002 |
| Subjective fatigue | ||
| 7343 K – DL | –4.302 | <.001 |
| 2564 K – DL | –3.223 | .004 |
| Subjective sleepiness | ||
| 3730 K – DL | –3.111 | .005 |
| 7343 K – DL | –5.936 | <.001 |
| 2564 K – DL | –5.905 | <.001 |
[i] Note. Only comparisons that were statistically significant are shown in the table. Bonferroni correction was applied and p ≤ 0.006 was set as statistically significant.
Figure 3
Means ± SE of normalized alpha power for 3730 K, 7343 K, 2564 K, and DL conditions in each trial for morning (a) and afternoon (b) sessions.
Note: Given that the alpha power was negatively correlated with light-induced alertness, the increment of alpha power indicates a reduction in objective alertness [14, 15, 44, 45].
Figure 4
Means ± SE of the normalized mean RT and accuracy for the 3730 K, 7343 K, 2564 K, and DL conditions in each trial for morning (a and b) and afternoon (c and d) sessions.
Figure 5
Means ± SE of the normalized HR, LF, HF and LF/HF power ratio for the 3730 K, 7343 K, 2564 K, and DL conditions in each trial for the morning (a, b, c, and d) and afternoon (e, f, g, and h) sessions.
Table 4
Means ± SE of the normalized subjective fatigue and sleepiness during each session.
| Light Condition | Session 1 | Session 2 |
|---|---|---|
| subjective fatigue | ||
| 3730 K | 1.153 ± 0.031 | 1.277 ± 0.044 |
| 7343 K | 1.116 ± 0.036 | 1.145 ± 0.048 |
| 2564 K | 1.086 ± 0.039 | 1.215 ± 0.048 |
| DL | 1.321 ± 0.042 | 1.43 ± 0.053 |
| subjective sleepiness | ||
| 3730 K | 1.178 ± 0.056 | 1.363 ± 0.096 |
| 7343 K | 1.043 ± 0.041 | 1.17 ± 0.071 |
| 2564 K | 1.098 ± 0.049 | 1.223 ± 0.085 |
| DL | 1.443 ± 0.068 | 1.595 ± 0.077 |