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The visibility range is defined from where one can see. And it can be changed by illuminance, the character size, and eyesight and so on. In this paper the visibility range of 120 students is measured for 4 character sizes and 3 illuminations in a classroom. In order to forecast the visibility range of unmeasured data, using least square approximation theory, functions whose independent variable is illuminance and whose dependent variable is the visibility range is proposed. Because the visibility range is invariant according to illuminance, common logarithmic functions for 4 character sizes are used. The small difference between the postulated functions and the measured data verifies the accuracy of the functions. Key Words : Illuminance, Least Square Approximation, the Visibility Range, the Character Size * Corresponding Author : Tae-Hyun Kim (Myongji College.) Tel: +82-2-300-3728 email: kth@mail.mjc.ac.krReceived October 24, 2013 Revised (1st November 28, 2013, 2nd December 6, 2013) Accepted January 9, 2014

Measurement and Forecast of the Visibility Range according to Illuminance and the Character Sizes