New parameters to evaluate the capability of a daylight-linked control system in complementing daylight

The use of daylight-linked controls (DLCs) can be a valuable design strategy to improve lighting conditions of indoor environment and to obtain considerable energy savings. These systems continuously adjust luminaires flux emission to maintain a constant illuminance level at the workplane, accounting for daylight availability. However, depending on their setting and operating conditions, they can provide more or less light than necessary, determining light excess or deficit at the workplane. Generally, the quality of control strategies is measured through achievable energy savings, but this approach is too inaccurate, since it does not inform about the ability of the system to provide adequate lighting conditions. Given that, the paper proposes new indices to describe DLCs performances: Daylight Integration Adequacy (DIA), Percentage Light Deficit (LD%), Percentage Intrinsic Light Excess (ILE%) and Percentage Light Waste (LW%). DIA (and complementary parameters DIA− and DIA+) describes the occurrence of different control operating conditions (ideal functioning, intrinsic light excess, light deficit and light waste) during a specific period. LD%, ILE% and LW% define the quantity of wasted or lacking light. Moreover, a simple case study is presented, in order to demonstrate the simplicity in calculating these parameters and their usefulness. •Achievable energy savings are not sufficient to describe daylight-linked controls performances.•New parameters are proposed to describe daylight-linked controls performances.•DLCs operating conditions are: ideal functioning, light deficit, intrinsic light excess, light waste.•New parameters describe the occurrence of operating conditions during a given period.•New parameters quantify light excess, light waste and light deficit in terms of light exposure.