Abstract
Quantifying and comparing light environments are crucial for interior lighting, architecture and visual ergonomics. Yet, current methods only catch a small subset of the parameters that constitute a light environment, and rarely account for the light that reaches the eye. Here, we describe a new method, the environmental light field (ELF) method, which quantifies all essential features that characterize a light environment, including important aspects that have previously been overlooked. The ELF method uses a calibrated digital image sensor with wide-angle optics to record the radiances that would reach the eyes of people in the environment. As a function of elevation angle, it quantifies the absolute photon flux, its spectral composition in red–green–blue resolution as well as its variation (contrast-span). Together these values provide a complete description of the factors that characterize a light environment. The ELF method thus offers a powerful and convenient tool for the assessment and comparison of light environments. We also present a graphic standard for easy comparison of light environments, and show that different natural and artificial environments have characteristic distributions of light.
Highlights
In diverse fields such as architecture, lighting science, visual ergonomics, environmental psychology and visual ecology, measurements of environmental light are often essential
Quantifying and comparing light environments are crucial for interior lighting, architecture and visual ergonomics
To quantify the biologically most relevant aspects of light environments we developed a technique based on a digital camera with a 180° fisheye lens
Summary
In diverse fields such as architecture, lighting science, visual ergonomics, environmental psychology and visual ecology, measurements of environmental light are often essential. A striking example is the extremely widespread use of lux-meters These measure illuminance with an upward-directed cosinecorrected angular sensitivity [1]. Illuminance readings quantify the light that reaches the environment, usually from above, whereas our experience of a light environment is based on light reaching the eye after it has been reflected, refracted or transmitted by the environment. This is a fundamentally important distinction, because the visual impression we get from the environment is not primarily concerned with the light sources, but with the objects, materials and surfaces that are illuminated
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