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The use of range lights in nautical navigation involves the visual determination of the vertical alignment of two points of light, in order to indicate the centre of the channel. In two experiments it is shown that this vernier alignment task is more accurate if illuminated linear stimuli are used as range lights. Experiment 1 involved a laboratory simulation and experiment 2 involved a field test with full sized range lights. The average reduction of error through the use of linear stimuli over the standard point stimuli, for navigational alignments at a distance of one-half nautical mile from the range lights, was 69-4%. This suggests that a marked safety advantage might accrue from the use of linear range lights for nautical navigation purposes.