Abstract
Natural illumination changes smoothly in chromaticity and illuminance through the day, yet we are largely unaware of all but the most rapid changes, at dawn and dusk. Previously, we have shown that discrimination of abrupt temporal changes in illumination chromaticity depends on the chromaticity of the reference (adapting) illumination; for more extreme chromaticities, changes towards neutral chromaticities are less easily discriminated than changes away from neutral (Aston et al., submitted). Here we examined discrimination of smooth temporal changes in illumination chromaticity along the daylight locus. We aimed to determine the minimum detectable velocity of chromaticity change in daylight metamers in an immersive illumination setting. Participants sat in a 2 m3 enclosure with matte white walls, illuminated by spectrally tunable LED lamps (Ledmotive; www.hi-led.eu). In each session, the participant first adapted for 2 minutes to the reference chromaticity (with correlated colour temperature (CCT) of 2000 K, 6500 K or 14000 K). Each trial began with 5 seconds of chromatic noise illumination, followed by a smooth change in illumination chromaticity away from the reference point along the daylight locus; the amount of change varied across trials while the duration was held fixed, or vice versa. Pilot results (n=4 participants) show that smooth change detection thresholds for bluish changes along the daylight locus are higher at 2000K than at 6500K and 14000K, consistent with the suggestion that illumination changes towards neutral are less easily detected than changes away from neutral.
Acknowledgement: EC H2020-MSCA-ITN (DyViTo)