# Encyclopedia of Color Science and Technology

2016 Edition
| Editors: Ming Ronnier Luo

# Luminance Meter

• Bor-Jiunn Wen
Reference work entry
DOI: https://doi.org/10.1007/978-1-4419-8071-7_359

## Definition

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.

## Introduction

The luminance of a light source (integrating sphere with known output aperture) is determined from the measurement geometry and illuminance measured by a photometer. The luminance of the light source is obtained as
$${L}_v=\frac{E_v{D}^2}{A}$$
(1)
where Ev is the illuminance at a distance D between the aperture plane of the source and the photometer; and A is the area of the source aperture. The distance A depends on the radius of the limiting aperture r 1 , the radius of the source r 2 , and the physical distance d between the source and the aperture according to Eq. 2.
$${D}_2={r}_1^2+{r}_2^2+d$$
(2)
Equation 2 is accurate within ±0.01 % for distances that are more than one decade greater than the radius [1].

## Applications

An imaging luminance measurement device (ILMD) is capable of measuring illuminance in an image. It can automatically quantify the light distribution or light uniformity. This is much more powerful than the conventional single-point luminance meter. For example, an ILMD is utilized for the fast imaging luminance measurement of flat panel displays [2]. Figure 1 depicts measurement of the luminance of vertical or horizontal patterns on a display with an ILMD in a slightly tilted position [2]. The subsequent image processing includes calculating the spatial frequency response (SFR) of the image using a slanted-edge algorithm, obtaining resolution at a specified decrease (e.g., 50 %) in the SFR of the device under test (DUT), and finally, specifying resolution in the sharpness of the DUT.
In addition, an automatic measurement system based on an ILMD also measures the photometric properties of road and tunnel lighting systems [3, 4]. Figure 2 depicts an automatic system for this purpose. Compared with a single-point luminance meter, an ILMD is more precise and time-saving for measuring road and tunnel lighting.

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. [3] 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.

## References

1. 1.
2. 2.
SID IDMS Information Display Measurements Standard, v1.03, 1 June 2012Google Scholar
3. 3.
Hsu, S.W., Chung, T.Y., Pong, B.J., Chen, Y.C., Hsieh, P.H., Lin, M.W.: Relations between flicker, glare, and perceptual ratings of LED billboards under various conditions. In: CIE Centenary Conference, Paris (2013)Google Scholar
4. 4.
CIE 194: On Site Measurement of the Photometric Properties of Road and Tunnel Lighting (2011)Google Scholar