Light interventions
sudden increase
Four ceiling luminaires (research prototypes developed by Bartenbach GmbH, Austria) provided ambient lighting for the test rooms. Each luminaire contained 48 warm-white LEDs (Luxeon Z-ES, 2219 K) and cold-white LEDs (Luxeon Z-ES, 5626 K) which together provided neutral-white light (4026 K; color rendering index: 93; CIE x/y coordinates: 0.379/0.374). Ambient lighting was maintained at a low level throughout the study (100 lx horizontal, at floor level) and met current indoor lighting standards (e.g., unified glare rating < 19, color rendering index > 80).The room lighting was supplemented by a task luminaire (research prototype developed by Bartenbach GmbH, Austria, as part of the EU-funded ‘REPROLIGHT’ project; see Workplace luminaire—profile view (In the present study, the color temperature of lighting was kept constant at 4026 K (color rendering index: 93; CIE x/y coordinates: 0.379/0.374). Spectral power distribution (see Fig. Relative spectral power distribution of the light intervention.Photometrical characterization of the light conditions.Note: measurements at eye level were done in a fixed position (i.e., 120 cm above floor level at the edge of the table with a horizontal viewing direction); measurements at desk level are the average of nine spot measurements equally distributed across the desk surface.Under the stronger light pulse condition, task illumination was initially increased from a corneal illuminance of 130 lx (86 m-EDI) to 1360 lx (900 m-EDI) over a 30-s period and remained there for 29.5 min. To generate a similar perceived sudden increase in task illumination in the weaker light pulse condition, illuminance was first decreased before being rapidly increased. Thereafter, corneal illuminance was to be imperceptibly dimmed to 130 lx over a period of several minutes. By using these lighting control strategies, the two light pulse conditions should be perceived as equal. To derive the appropriate dimming dynamics for the weaker light pulse condition, a small pilot study was conducted within the project team (n = 5 subjects). Finally, the weaker light pulse condition was specified as follows: illuminance was first reduced by 50% to 65 lx at eye level within 30 s and then immediately increased to 870 lx at eye level (576 m-EDI) within 15 s (see Table As discussed earlier