Abstract

We evaluate the daylight performance visual comfort buildings by measuring light in luminance and illuminance using luminance and lux meter respectively. Detailed measurements of illuminance in a space using these methods on a grid can be time-consuming, while luminance meters to measure luminance values are quite expensive. Recent studies indicate that luminance-based metrics have the best fit to occupant responses in visual comfort surveys. But High Dynamic Range (HDR) techniques can quickly capture a large field of view at a high resolution and can be done with DSLR cameras that are more accessible than luminance meters. This research goes one step further to evaluate the HDR acquisition method using even more accessible smartphone cameras. The method includes calibration of the HDR images using lux meters which are affordable and easily available. A variety of smartphone cameras were evaluated in a wide range of brightness conditions in a scene. The error between the low-cost HDR approach and the conventional approach of HDR imaging is determined and a method for correction factors is proposed. Vignetting corrections for the smartphone camera lens have been demonstrated. A visual comfort survey of a primarily daylit workshop space is done to document as a test case to evaluate the feasibility and accuracy of the low-cost HDR approach. Lux meter for calibration of HDRI images is found to be reasonably accurate (average error of 7%). Of the 6 smartphones studied, the maximum luminance was captured by iPhone 6 and which could only capture 17% of the measured luminance. The fisheye lens used in this study increases the FOV from 68º (no fisheye) to 136° (with fisheye) but the FOV outside 100° was not useful due to large vignetting effect.