Glare due to high luminance ratios is a common problem in buildings with windows, clerestories or skylights. A number of advanced window and skylight systems are being developed as part of an ongoing study aimed at reducing glare and improving lighting quality. To evaluate the effectiveness of these alternative systems, researchers must measure luminance distributions (a.k.a. luminance maps) under real daylight conditions, over different times of the day and throughout the year. To do that, CLTC researchers have developed a simple, effective, automatic technique using HDR time-lapse photography and a means of validating the measured results using high-accuracy, calibrated luminance meters. Anothai Thanachareonkit, Ph.D, presented these findings at the 2011 CISBAT conference, where she won a Best Poster Award.

Click on the image above to see the poster. Graphic designer: Kathreen Fontecha.

The goal of this project is to develop an accurate, automatic means of measuring luminance distributions for daylighting performance assessment.

DESCRIPTION:
The approach is based on the use of a Canon point-and-shoot digital camera with the Canon Hack Development Kit (CHDK), which allows use of UBASIC scripts that automatically set exposure to prescribed values and take photographs at prescribed time intervals. The photographs are automatically transferred to a remote computer using a wireless memory card; they are then combined into luminance distributions using Photosphere software.

RESULTS:
With the appropriate calibration, the luminance values acquired using this technique are reasonably close to those gathered with a conventional spot luminance meter.