Effect Of Five Different Light Sources On Matching 25-Pair Telephone Cable.

Background: Analog telephone service is commonly transmitted using 25-pair telephone cable. The fifty copper wires inside the cable are twisted into twenty-five pairs and organized with a color coding system where each pair has its own two-color combination. Although there are twenty-five different two-color combinations, only ten total colors are used, and it may be difficult to distinguish among many of the pairs. The objective of this study is to determine the effects of five different light sources (illuminant C, an incandescent lamp, a fluorescent lamp, a metal halide lamp, and a sodium vapor lamp) on the ability to accurately distinguish among each of the twenty-five pairs of wires.
Methods: Thirty-three optometry students with normal color vision were tested. Sections of each of the twenty-five pairs of cable were aligned in random order on one side of a poster board and labeled 1-25. On the other side, sections of each pair were aligned in random order and labeled A-Y. Subjects were asked to match each numbered pair of wires with the pair on the other side with the same two-color combination. The test was repeated and timed under each of the five different light sources. Results: Subjects made more errors with sodium vapor which was shown to be a statistically significant difference when compared to the other four illuminants. There were also statistically significant differences in the completion times between many of the illuminants. Conclusions: The source of illumination affects the ability to accurately and efficiently match pairs of 25-pair telephone cable.