Contributed talks II: Characterizing terrestrial illumination: Spectral, angular, spatial, and temporal variability

Area of Science:

• Environmental Science
• Human Physiology
• Chronobiology

Background:

• Terrestrial light changes spectrally, spatially, and temporally due to diurnal cycles and atmospheric conditions.
• Light exposure acts as a crucial "zeitgeber" (time giver), influencing human physiology and behavior by regulating biological rhythms.

Purpose of the Study:

• To analyze spectral light-field data outdoors from dawn to dusk under varying weather conditions.
• To investigate the physiological implications of light variations on circadian regulation via photoreceptors.
• To compare spectral differences between diffuse and directional light components and assess haze effects.

Main Methods:

• Collected spectral light-field data over four days in Delft (sunny and cloudy) and Newcastle (overcast).
• Decomposed light fields into diffuse and directional components to analyze spectral composition.
• Examined variations in α-opic illumination vectors and their alignment with photoreceptor sensitivities.

Main Results:

• Overcast conditions showed reduced light variability due to increased scattering, altering spectral composition.
• α-opic illumination vectors varied with weather, aligning with photoreceptor sensitivities under clear and cloudy skies.
• Haze shifted chromaticity towards blue, potentially increasing melanopic efficiency, but dawn/dusk light variations are more significant for circadian regulation.

Conclusions:

• Weather significantly impacts terrestrial light's spectral and directional properties, influencing photoreceptor responses.
• While daily light fluctuations are substantial, dawn and dusk light transitions are the primary drivers of circadian rhythm regulation.
• Understanding light variability is crucial for comprehending its role in human biological timing.