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.