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The effect of test distance on the CN lantern results

Published online by Cambridge University Press:  06 September 2006

JEFFERY K. HOVIS  and
SHANKARAN RAMASWAMY
JEFFERY K. HOVIS
Affiliation:
School of Optometry, University of Waterloo, Waterloo, ON, Canada
SHANKARAN RAMASWAMY
Affiliation:
School of Optometry, University of Waterloo, Waterloo, ON, Canada
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Abstract

The purpose of this study is to determine how the viewing distance affects the pass/fail results of the CN Lantern (CNLan). The CNLan is a color vision test designed for the railway industry. It presents 15 triplets of colored lights that could be any combination of red, green and yellow. The test was viewed from 4.6 m and 2.3 m. Sixty-seven color-defectives participated in the first part of the study. Sixty-six percent of the subjects repeated the experiment 10 days later. There was a significant (P < 0.05) decrease in the mean number of errors from 7.6 to 4.3 as the distance decreased. There was also a corresponding increase in the percentage of subjects who passed from 9.0% at 4.6 m to 20.9% at the 2.3 m viewing distance. None of the subjects who passed at the longer distance failed at the shorter distance. The replication results were statistically identical to the first session (P > 0.05). Decreasing the CNLan viewing distance by 50% does decrease the number of errors and increase the pass rate. This indicates that some color-defectives could work in the railway yards where the sighting distances for the signal lights are shorter than on the main track.

Keywords

LanternColor vision testRailwayCN LanternColor vision standards
Type
TESTING AND METHODS
Information
Visual Neuroscience , Volume 23 , Issue 3-4 , May 2006 , pp. 675 - 679
Copyright
© 2006 Cambridge University Press

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