Table 1.
Mean ± standard deviation (SD) errors in photopic illuminance measurements, relative to a calibrated meter (Gigahertz-Optik), from six Daysimeter (Daysimeter-D) and six Actiwatch Spectrum devices under diffuse illumination from six different practical light sources.
| Source | Calibrated light meter (lux) | Daysimeter (lux) | Daysimeter measurement error (%) | Daysimeter measurement range (lux) | Actiwatch (lux) | Actiwatch measurement error (%) | Actiwatch measurement range (lux) |
|---|---|---|---|---|---|---|---|
| Philips | 427 | 430±5.83 | 0.65±1.37 | 422 – 440 (range = 4%) | 585±20.5 | 37.1±4.80 | 564 – 619 (range = 9%) |
| F32/T8/TL/735 (3500 K fluorescent) | |||||||
|
| |||||||
| GE | 193 | 191±2.37 | −1.21±1.22 | 188 – 195 (range = 3%) | 332±13.5 | 71.9±6.99 | 309 – 349 (range =11%) |
| F55BX/AR/FS (9000 K fluorescent) | |||||||
|
| |||||||
| Sylvania LU 250 (high pressure sodium) | 103 | 96.4±2.49 | −6.70±2.41 | 92.1 – 99.0 (range = 7%) | 40.2±1.54 | −61.1±1.49 | 38.3 – 48.3 (range = 20%) |
|
| |||||||
| Daylight | 1944 | 1950±31.4 | 0.29±1.61 | 1920 – 1991 (range = 4%) | 3886±160 | 99.9±8.20 | 3649 – 4141 (range = 12%) |
|
| |||||||
| Beta Edge 5760 K | 75.4 | 71.5±0.89 | −5.27±1.18 | 70.2 – 72.5 (range = 3%) | 81.9±6.39 | 8.54±8.48 | 73.4 – 89.7 (range =18%) |
| LED | |||||||