A Better Photometric Index of Photo-Biological Effect on Visual Function of Human Eye: Illuminance or Luminance?

Jianqi Cai,Wentao Hao,Shanshan Tang,Jiajie Fan,Rongrong Wen,Yutong Li,Shanshan Zeng,Ping Tang,Lijun Pan,Ya Guo

doi:10.1109/access.2019.2953552

Abstract

The illuminance index has been widely used in the field of photometry, although the luminance contains more information on not only light intensity but also light direction. In this study, we clarify which photometric index is more competent to describe the influence of lighting environment on human eye. In this study, we propose a novel methodology to investigate the photo-biological effect of the lighting environment by human factor experiment. With the human factor experiments performed on 20 participants, we compare the variations of ocular responses during the Landolt-rings-counting visual task in lighting environments with similar illuminance while distinct luminance changes. With the same Correlated Color Temperature (CCT) and Spectral Power Distribution (SPD), optical performances with similar illuminance values present quite different influences on ocular responses, and the response variations are found to vary with luminance values. It is implied that the regularity of luminance influence on the ocular responses to lighting environment is likely to be dependent on luminance value instead of illuminance, and the photometric index luminance seems more appropriate to be used to assess the lighting quality in standards.

Highlights

Photometry is the foundation of optical measurement since it proposes definitions of physical indices and provides guidance for the design and production of optical instruments [1], [2]
Through comparing the influence of illuminance and luminance on ocular physiological parameters, this study figures out the key photometric index which presents obvious influence on human eye
The lighting environments are constructed by two kinds of lamps with similar illuminances but obviously different luminance on six desks

Summary

Introduction

Photometry is the foundation of optical measurement since it proposes definitions of physical indices and provides guidance for the design and production of optical instruments [1], [2]. The popularity of illuminance is likely to be the convenience of its measurement and data handling, since its definition is the luminous flux (radiation power perceived by human eye). The illuminance contains information of light intensity as a photometric index. Another photometric index luminance describes the brightness of the lighting environment or lighting source [6]–[8]. The definition of luminance is the luminous flux reflected from a certain surface (light intensity from the unit surface light source in certain direction). The photometric index luminance contains information of light intensity and light direction. The luminous flux of light source and reflection surface is likely to change in different directions [9], [10].

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