Continuous Overcast Daylight Autonomy (DAo.con): A New Dynamic Metric for Sensor-Less Lighting Smart Controls

ABSTRACT

Daylight dynamic metrics are useful tools for quantifying the switch-on time or the dimming of electric lighting according to the architectural scenario. A variant of these metrics can also be used to define strategies to control the lighting fixtures, dimming the luminous flux with no need for external input and reducing therefore the energy consumption of the lighting systems. Given this context, a new approach is proposed, Continuous Overcast Daylight Autonomy (DAo.con), defined as the percentage of occupied time when an illuminance threshold is met by daylight alone under continuous overcast sky conditions, considering a partial credit linearly to values below the threshold defined. This concept acts as an algorithm which adjusts the luminous flux of the luminaires according to the Daylight Factors measured or simulated, considering user requirements and ignoring any internal device for actively measuring the lighting conditions. The Daylight Factors can be modified according to the use of shading devices that affect to the indoor natural light. Accordingly, this algorithm can significantly reduce the embodied cost of the lighting smart controls, promoting their spread and its implementation in building refurbishment, while the energy consumption in electric lighting is reduced by up to 76% for large windows and by up to 65% for medium-sized openings. The results show that the use of this algorithm in office environments with LED fixtures can promote energy savings of up to 7.8 W/m² for locations with predominantly clear skies and up to 5.7 W/m² for northern latitudes with mainly overcast skies.

KEYWORDS:

• Daylighting
• energy management
• daylight factor
• daylight autonomy
• indoor lighting

Abbreviations

DF	=	Daylight Factor
DA	=	Daylight Autonomy
DAcon	=	Continuous Daylight Autonomy
DAo	=	Overcast Daylight Autonomy
DAo.con	=	Continuous Overcast Daylight Autonomy
sDA	=	Spatial Daylight Autonomy
wfi	=	Weighting factor
Lz	=	Luminance at the zenith
Ei.o	=	Indoor illuminance calculated under overcast sky
Eo.o	=	Outdoor illuminance calculated under overcast sky
Emi.o	=	Indoor illuminance measured under overcast sky
Emo.o	=	Outdoor illuminance measured under overcast sky
Eml	=	Indoor illuminance under electric lighting
Et	=	Illuminance threshold

Acknowledgments

The authors wish to express their thanks for all the technical and financial support provided, including the research project: CARELight_Lite: Biodynamic lighting for circadian rhythm regulation of healthcare personnel in Pediatric Intensive Care Units (Ref PI-0136-2019). The authors are grateful to all those who collaborated in this research project, especially to Blas de Lezo for encouraging this article.

The authors also wish to thank the Junta de Andalucía and the University of Seville for providing the test cell facilities which made it possible to validate the metrics used in this research.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The results presented were funded by the Agencia Estatal de Investigación (AEI) and the Ministerio de Ciencia e Innovación (MCIN) of the Government of Spain through the research projects CHRONOLIGHT: Biodynamic wide spectrum lighting for biological chronoregulation and pathogens neutralization in hospital facilities (Ref PID2020-117563RB-I00) and NEUROLIGHT: Efficient design for biodynamic lighting to promote the circadian rhythm in hospital facilities (Ref PDC2021-120807-I00).