Correspondence: A panoramic light meter

Abstract

The selection of papers chosen for issue 54(7) of Lighting Research and Technology leads me to suggest that we are on the verge of a breakthrough that has the potential to transform how practitioners make use of measurement to relate lighting technology to its applications. This has arisen because several companies have recently introduced 360-degree panoramic cameras which comprise a pair of backto-back 180-degree digital cameras in a compact device. Such a camera can be mounted on a tripod to produce a high dynamic range image of the entire three-dimensional (3-D) field, and this image can be downloaded as a single file to a screen device, such as a laptop or phone, for a range of viewing options. The two papers in that issue by Li and Cai1,2 introduce a procedure by which a practitioner can use an illuminance meter, or better a luminance meter, to calibrate such a camera to generate panoramic luminance files that can be linked to Radiance software to enable direct measurement of metrics such as relative visual performance or unified glare rating. The ability to measure such aspects of lighting in actual applications, which could include variations of sunlight and daylight, has the potential to transform the enforcement lighting standards in workplaces. But that would be just the start. Practitioners would be able to routinely examine how the 3-D light field influences the appearance of lit objects, which might range from 3-D work tasks to peoples’ facial features, and to explore how the differences of appearance may be described in terms of flow of light concepts, such as modelling or 3-D lighting patterns that may be specified by vector and scalar illumination metrics.3 Furthermore, the technique devised by James Duff and his colleagues4 for separating the direct and indirect flux fields could be applied to enable ambient illuminance at a measurement point to be recorded in terms of mean indirect cubic illuminance,5 or for the mean room surface exitance3 for an indoor space to be readily determined. Practitioners would be able to assess the role of lighting diversity (as opposed to uniformity) for achieving controlled distributions of visual emphasis for selected target objects, and to specify distributions of target/ambient illuminance ratio3 values for application in lighting projects using the Lighting Design Objectives (LiDOs) Procedure.3 Lighting standards specified in terms of ambient illuminance would be enforceable, and a whole range of LiDOs that practitioners might choose to specify for specific applications would become verifiable. This development in camera technology could lead to the prime objective of lighting practice switching from imparting visibility to tasks to creating luminous environments for people to respond to a distinct step closer.