Figure 1
Spectral power distribution of the high (17000 K) correlated colour temperature lamps. The spectral power distributions of typical 3000 K and 4000 K fluorescent lamps are plotted for comparison.
Table 1
Horizontal and vertical desk illuminance values on the intervention and control floors.
| Floor | Average horizontal illuminance at working plane (SD) | Average % daylight contribution to horizontal illuminance (SD) | Average vertical illuminance at the eye position (SD) | Average % daylight contribution to vertical illuminance (SD) |
| A. Intervention (17000 K) | 311 lux (112) | 13% (10) | 170 lux (85) | 40% (33) |
| B. Control (2900 K) | 354 lux (45) | 11% (10) | 128 lux (44) | 55% (32) |
Table 2
Distribution of Modified Columbia Scale scores examined by group and time period.
| Baseline | Study End (3 months) | % change | Unpaired t test (df = 67) | Paired t test (df = 22) | Paired t test (df = 45) | Unpaired t test (df = 67) | |||||
| Item No. | Description | Control (n = 23) | Intervention (n = 46) | Control (n = 23) | Intervention (n = 46) | Control | Intervention | Baseline comparison | Control change | Intervention change | 3 month comparison |
| mean (SD) | mean (SD) | mean (SD) | mean (SD) | t statistic | t statistic | t statistic | t statistic | ||||
| 1 | Fatigue/tiring easily? | 2.9 (0.9) | 2.9 (1.1) | 2.7 (1.1) | 2.1 (1.0) | 7.6 | 26.9 | -0.16 | 0.93 | 4.04** | 1.76 |
| 2 | Trouble concentrating | 2.5 (1.1) | 2.9 (1.2) | 2.5 (0.9) | 1.8 (0.9) | 1.7 | 36.8 | -1.23 | 0.21 | 5.84** | 3.46* |
| 3 | Physical clumsiness? | 2.0 (1.1) | 1.7 (1.0) | 1.6 (0.6) | 1.5 (0.9) | 21.7 | 13.7 | 1.02 | 1.93 | 1.48 | -0.70 |
| 4 | Decreased daytime alertness? | 2.7 (1.1) | 2.5 (1.2) | 2.1 (0.8) | 1.8 (0.8) | 21.0 | 28.1 | 0.74 | 2.73 | 3.96** | 0.45 |
| 5 | Trouble with memory? | 2.4 (1.3) | 1.9 (1.1) | 2.1 (0.8) | 1.5 (0.7) | 12.5 | 21.3 | 1.65 | 1.07 | 2.80 | 0.38 |
| 6 | General feelings of weakness | 2.0 (1.1) | 2.0 (1.0) | 1.7 (0.7) | 1.4 (0.8) | 17.0 | 26.7 | 0.33 | 1.56 | 3.60* | 0.67 |
| 7 | Light-headed & dizzy | 2.2 (1.4) | 2.1 (1.3) | 2.0 (1.1) | 1.4 (0.8) | 9.8 | 33.7 | 0.26 | 1.10 | 4.04** | 1.74 |
| 8 | Lethargy/sluggish feelings? | 3.0 (1.0) | 2.7 (1.3) | 2.3 (0.8) | 1.8 (0.8) | 23.5 | 31.7 | 0.93 | 3.43* | 5.07** | 0.55 |
| 9 | Sleepiness in day | 3.0 (1.2) | 2.8 (1.2) | 2.6 (1.0) | 1.9 (0.7) | 14.5 | 31.0 | 0.66 | 2.47 | 4.90** | 1.55 |
| 10 | Work performance | 7.0 (1.7) | 6.4 (1.5) | 7.3 (1.6) | 7.6 (1.4) | 4.4 | 19.4 | 1.45 | -1.16 | -6.07** | -2.72 |
| 11 | Alertness and concentration | 6.2 (1.8) | 6.1 (1.9) | 6.8 (1.7) | 7.5 (1.8) | 9.9 | 22.9 | 0.23 | -2.13 | -4.34** | -1.57 |
| Combined Score (first 9 items) | 22.7 (7.5) | 21.5 (8.3) | 19.5 (5.2) | 15.4 (5.7) | 14.3 | 28.6 | 0.59 | 2.60 | 5.22** | 1.53 | |
* = p < 0.05, ** = p < 0.001 equivalent after applying Bonferroni correction
Table 3
Distribution of selected SF-36 combined measures by group and time period.
| Baseline | Study End (3 months) | % change | Unpaired ttest (df = 67) | Paired ttest (df = 22) | Paired ttest (df = 45) | Unpaired ttest (df = 67) | |||||
| Item No. | Description | Control (n = 23) | Intervention (n = 46) | Control (n = 23) | Intervention (n = 46) | Control | Intervention | Baseline comparison | Control change | Intervention change | 3 month comparison |
| mean (SD) | mean (SD) | mean (SD) | mean (SD) | t statistic | t statistic | t statistic | t statistic | ||||
| GH | General Health | 65.5 (22.4) | 67.8 (20.5) | 70.3 (22.0) | 73.8 (17.0) | 7.4 | 8.7 | -0.44 | -1.57 | -2.33 | -0.25 |
| V | Vitality | 43.2 (23.5) | 48.4 (20.4) | 50.5 (19.0) | 62.1 (17.1) | 17.0 | 28.4 | -0.94 | -1.95 | -4.44** | -1.25 |
| SF | Social Functioning | 63.6 (27.7) | 75.0 (25.4) | 81.0 (19.5) | 85.6 (17.7) | 27.4 | 14.1 | -1.71 | -3.35* | -3.09 | 1.11 |
| RE | Role Emotional | 77.5 (29.1) | 80.8 (23.8) | 80.4 (27.9) | 86.1 (19.5) | 3.7 | 6.5 | -0.50 | -0.56 | -1.53 | -0.39 |
| MH | Mental Health | 62.8 (22.2) | 64.3 (20.5) | 67.8 (16.8) | 73.3 (15.8) | 8.0 | 13.9 | -0.28 | -1.78 | -3.42* | -0.93 |
* = p < 0.05, ** = p < 0.001 equivalent after applying Bonferroni correction
Table 4
Areas of substantial improvement in the intervention group compared to baseline measures (where a concomitant improvement was not observed in the control group).
| Area | Description | Percentage Improvement over baseline measure |
| Fatigue | Item of original Columbia Scale | 26.9% |
| Concentration | Item of original Columbia Scale | 36.8% |
| Daytime Alertness | Item of original Columbia Scale | 28.1% |
| Feelings of Weakness | Item of original Columbia Scale | 26.7% |
| Light-headedness | Item of original Columbia Scale | 33.7% |
| Sleepiness | Item of original Columbia Scale | 31.0% |
| Work Performance | Additional item (derived from WHO-HPQ) | 19.4% |
| Alertness & oncentration | Additional item | 22.9% |
| Vitality | Combined measure from SF-36 | 28.4% |
| Mental Health | Combined measure from SF-36 | 13.9% |
Table 5
Trouble concentrating or thinking clearly at baseline, week 7 and week 14 by group. Mean score derived from the Columbia Scale according to response to the second question, "Over the last 3 days how much have you been bothered by trouble concentrating or thinking clearly? Possible answers and scoring: 1 = not at all, 2 = a little bit, 3 = moderately, 4 = quite a bit, 5 = extremely.
| Time point | Control (n = 23) | Intervention (n = 46) |
| mean score (SD) | mean score (SD) | |
| Baseline | 2.5 (1.1) | 2.9 (1.2) |
| Week 7 | 2.6 (1.1) | 1.9 (0.9) |
| Study end (Week 14) | 2.5 (0.9) | 1.8 (0.9) |
Figure 2
Percentage change in reported 'trouble concentrating or thinking clearly' during the preceding 3 days. The plot shows data from 7 and 14 weeks after baseline in control and intervention groups (error bars represent 95% confidence interval for the mean change).