Methods to Describe and Measure Lighting Conditions in Experiments on Non-Image-Forming Aspects

Abstract

Research indicates that spectral distribution and the direction of the light received at the eye are relevant parameters in studies looking into non-image-forming effects. Nonetheless, lighting conditions are often described with vertical illuminance at the eye and correlated color temperature only, both of which are integral measurements that are not appropriate to give information about the spatial distribution of light and its spectrum. This article describes approaches for spatially and spectrally resolved measurements to properly quantify lighting conditions in research on nonimage-forming effects. The overview of measuring methods indicates that the spectral irradiance, when combined with a luminance image of the lighting setting, is an adequate measure in a large number of research approaches. Nonetheless, lighting conditions in experimental setups with different light sources or various surface reflectances require a higher resolution of detail. Four examples of devices are presented that can be applied in different experimental setups or lighting settings. A decision scheme is included to support the selection of the most suitable measuring equipment. The article concludes with a proposal for analysis and representation of the measurements.

Calculating luminous flux radiated to a camera lens via high dynamic range photogrammetry

“…A recent study proposed a concept of light incidence (J=dφ/dΩ), which is the incident luminous flux from a field of view of interest (or a portion of it) to a measurement point (e.g., meter sensor, human eye, or camera lens), evaluated per unit solid angle of view, similar to the definition of incident light intensity. 13,14 Moreover, Cai 6 developed HDR photogrammetry for measurement of synchronous per-pixel luminance and geometry (in the world coordinates XYZ of object space) of any target point in the field of view, using different types of lenses (including a 4.5-mm circular fisheye lens, a 10-mm fisheye lens, a 10- to 20-mm zoom lens, and a 30-mm standard lens). With self-calibrations, Cai’s HDR photogrammetry can be used on any type of camera and lens suitable for HDR imaging.…”

Human-Centric Lighting: Foundational Considerations and a Five-Step Design Process

“…It should also be understood that instantaneous measurements may not be representative of mean light exposure, which is almost always transitory and varies with things such as view direction, instantaneous daylight exposure, and lamp aging factors such as lumen depreciation and spectral changes with time. There are recommendations for measurement and reporting of light exposure in experiments ( 42 , 43 ), with some recommendations being transferable to field settings. Spectral lighting software is available to investigate some of these measures via simulation ( 44 , 45 ).…”

Human-centric lighting: Myth, magic or metaphor?

“…Clearly, quantifying the biological potency of light is still in its infancy. The scientific community is confronting how to characterise light for research, 65,77–80 with considerations that apply equally to integrative lighting. Despite the knowledge gaps, however, in the next section we hope to offer relief by explaining that it is possible to apply a core set of principles to the practice of integrative lighting.…”