Visual Performance for Incandescent and Solid-State Cap Lamps in an Underground Mining Environment

Miners depend most heavily on visual cues to recognize underground mining hazards; consequently, illumination plays a critical role in miners' safety. Some hazards are located in the miners' peripheral field of view (10° to about 60° off axis) or on axis (0°). The objective of this research was to determine if there were visual performance improvements when using solid-state cap lamps with light-emitting diodes (LEDs) as compared to incandescent light bulbs commonly used in miner cap lamps. Recent research has indicated that an increased short-wavelength content of the spectral power distribution of LEDs relative to incandescent lamps improves peripheral visual performance for low-light (mesopic) conditions. The visual performances of nine subjects were quantified by measuring the subjects' speed and accuracy in detecting floor objects located on axis and at ±20° off axis. The objects were located near field (1.83 m) and far field (3.66 m). Upon presentation of the objects, the subjects would count and point to each object using a red-laser pointer. The object detection response time and number of missed objects were recorded. The results of the visual performance comparison for an LED, a prototype LED, and an incandescent cap lamp are presented. There were no missed objects when the subjects used the LED-based cap lamps, but there were three missed-object occurrences when the subjects used the incandescent cap lamp. The mean detection time when using the incandescent cap lamp was 55.3% greater than that of the prototype LED cap lamp and 43.5% greater than that of the LED cap lamp. It can be inferred from these data that the spectral distribution of LED-based cap lamps could enable significant visual performance improvements as compared to incandescent cap lamps.