Lighting performance and electrical energy consumption of a virtual window prototype

This article discusses the design and evaluation of a virtual window prototype, built using arrays of LED tiles to simulate the light as well as the view of a window. Arrays of white light LED fixtures with adjustable colour temperatures were incorporated to provide direct light into the test room. Lighting performance was evaluated by measuring horizontal illuminance on the workplane, vertical illuminance on the observer’s eye plane, and luminance perceived by the observer at four vertical points. For estimating the electrical energy consumption, real-time power consumption of the entire system was measured, and three daily usage profile scenarios and two annual modes were considered. In addition, five locations were chosen to represent various climate types. The results show that under the maximum setting, the average workplane illuminance was 239lx for the test room used, whereas discomfort glare at the observer’s positions was classified as imperceptible. Patches of direct light on the side walls could be created as an intended effect from installing the direct light source arrays. Variation of average annual space availability within a given location as a function of usage profile is found to be very small; the values are however sensitive to the chosen criterion of workplane illuminance. Based on the designated daily usage profiles and annual modes, the normalised, total annual electrical energy consumption in all climate types is on average within the range of 0.63–0.79, relative to the total electrical energy consumed by the prototype when it constantly displays the maximum intensity setting.