Design and validation of a compact embedded photometric device for real-time daylighting computing in office buildings

Abstract

Studies have shown that the exposure to daylight can have substantial visual/non-visual benefits for building occupants. To optimise daylighting provision while maintaining a comfortable visual environment, daylighting control systems have been investigated by architectural design and academic research for a number of years. However, real-time regulation of daylighting in buildings requires transient daylighting simulation with high accuracy and, daylighting simulation, as performed to date, is significantly impacted by the employed sky luminance distribution models which only crudely reproduce the real sky characteristics due to oversimplification and limited luminance sampling inputs. In this paper, an embedded photometric device is proposed to combine high dynamic range (HDR) imaging based highresolution sky luminance monitoring with quasi real-time on-board daylighting computing, composed of a low-cost image sensor and a field programmable gate array (FPGA) microprocessor. A deliberate calibration procedure of the whole imaging system, regarding its spectral response (spectral correction error f'1 = 8.89%), vignetting effect and signal response, was formulated and validated experimentally. The device was made to measure a wide luminance range (150 dB) including that of the direct solar disk, sky vault, and landscape simultaneously. Finally, experiments during predominant clear and overcast sky conditions were conducted respectively to assess its performance in daylighting simulation, both qualitatively and quantitatively. The experimental results demonstrated its quality in solar tracking as well as its capability to reduce daylighting simulation error to 1 7 ∼ 1 3 of that of a common practice using the conventional Perez all-weather sky model for workplane illuminance calculation in office buildings.

Split-pane electrochromic window control based on an embedded photometric device with real-time daylighting computing

“…The design of the automated EC glazing integrates an embed-ded photometric device (EPD) [41] that is attached on the glass, with its imaging system targeted towards outdoors as illustrated in Figure 1, to control glazing tints to improve visual comfort for occupants, as a standalone system. The EPD acts as both a sensing unit and a controller for the EC glazing.…”

“…The EPD, proposed and demonstrated by Wu et al [41,42], mainly comprises a low-cost image sensor, lens, and a field pro-grammable gate array (FPGA) processor. The imaging system of the EPD was deliberately calibrated in the spectral response, vignette effect, signal response curves, and geometric mapping.…”

“…Although the EPD was demonstrated in its capability of real-time lighting simulation of workplane illuminance by Wu et al [41,45] in several studies, a cross comparison experiment was conducted to further assess the performance of EPD in WPI, image rendering, and DGP calculation in the testbed with static tinted EC glazing.…”

HDR Imaging for Luminance and Melanopic Radiance: Cameras and Spectral Power Distributionsract Title

“…Second, the camera spectral responsivity does not necessarily align with the sRGB responsivity. For instance, Wu et al indicated that the spectral responsivity of the camera can have severe disparity with the RGB colour space as manufacturers aim to achieve compelling colours (Wu et al, 2019). As a result, different cameras, with different spectral responsivities, might have varying capabilities in terms of luminance distribution measurements.…”

Spectral tuning of luminance cameras: A theoretical model and validation measurements

“…Moreover, Wu et al . 18 indicate that the spectral responsivity of the camera can have a severe disparity with the RGB colour space as manufacturers aim to achieve compelling colours. The sRGB colour space is a rendered or output-referred colour space designed for an output medium, 11,17 while HDR images are scene-referred images because the pixels are directly related to the radiance of the captured scene 11 .…”