Abstract
The evaluation of both visual and nonvisual effects from the spectral power distribution (SPD) of outdoor light is critical in lighting design. The dome-light SPD characteristically changes continuously depending on the seasonality, orientation, altitude of the sun or hour of the day. Traditional photopic parameters, such as the illuminance, luminance or correlated colour temperature (CCT), have been widely studied, but presently, there is no melanopic measurement or evaluation method. This article discusses the processes involved in establishing a simple method to determine the SPD of daylight and solar radiation over the skydome in a location to accurately account for the effects of both photopic and circadian levels around a location. Once per month for one year, natural daylight was spectrally measured in the city of Zaragoza (Spain); radiometric and photometric characteristics were analysed by season; and circadian effects were calculated in terms of standard parameters described by the Commission International de l’Eclairage (CIE), factors recommended by normative and scientific backgrounds. Finally, we suggest that the best parameter is the melanopic versus photopic irradiance ratio, which achieves reliable results at simplifying and correlating calculations.
Highlights
The sun is the main source of natural light on Earth; and as natural light passes through the atmosphere, its energy is manifested in the different types of radiation along the electromagnetic spectrum, measured from the ground
The Commission International de l’Eclairage (CIE) defines the Standard General Skies in the CIE S 011:2003/ISO 15469:2004 [1] as a mathematical model based on the variation in three characteristics: sky clearness and brightness, both derived from a comparison of direct normal and diffuse horizontal irradiance (W/m2 )
The methodology of this research was based on the analysis of the radiometric behaviour of the daylight at a location, which serves to model their circadian contribution at this same point
Summary
The sun is the main source of natural light on Earth; and as natural light passes through the atmosphere, its energy is manifested in the different types of radiation along the electromagnetic spectrum, measured from the ground. The amount of visible energy that reaches us depends on the atmosphere. Visible energy can be absorbed, reflected and scattered in all directions by gas and dust particles and clouds of water vapour. The characteristics of the entire sky can change within minutes, so overcast, partly cloudy and clear skies are highly dynamic due to winds. The Commission International de l’Eclairage (CIE) defines the Standard General Skies in the CIE S 011:2003/ISO 15469:2004 [1] as a mathematical model based on the variation in three characteristics: sky clearness and brightness, both derived from a comparison of direct normal and diffuse horizontal irradiance (W/m2 )
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