A luminance meter is a device used to measure the photometric unit, luminance, in a particular direction at a solid angle from a surface. The simplest devices measure the luminance in a single direction, while imaging luminance meters measure luminance in much the same way that a digital camera records color images.
Since the rapid growth of light-emitting diode (LED) technologies, the adjustable lighting on billboards using LED have become increasingly popular. Many of these products are pushed to much higher contrast in spatial and/or temporal configurations to attract attention. However, the glare and/or flicker of the LED sources may produce an uncomfortable visual experience. Therefore, Hsu et al.  proposed a measurement system for regulating between flicker and glare by using perceptual ratings of LED billboards under various conditions. In this research the authors performed both objective and subjective evaluations of flashing LED billboards in interior spaces. The objective flicker and glare evaluations were carried out by taking temporal and spatial measurements respectively. The properties of the flicker and glare values obtained are reproduced under physical conditions. The visual results were modelled by simple equations as a function of objective measurements in terms of a low-pass flicker index and unified glare rating. Thus, an effective method was developed for regulating the degree of flashing LED lighting using an ILMD.
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