title: When yellow lights look red: tinted sunglasses on the railroads.
abstract: OBJECTIVE
  A major Canadian railway company purchased safety eyewear sunglasses that were purported to have a neutral gray tint and that met the North American occupational and fashion sunglass requirements for signal light transmittance. After several weeks, the company began to receive reliable reports from employees that the yellow wayside signal appeared red when viewed through these sunglasses. Furthermore, the lenses themselves appeared to have a greenish brown tint rather than gray as the labeling implied.
  
  
  METHODS
  The transmission properties of the lenses were measured with a spectrophotometer, and color shifts were calculated for both roadway and railway signal lights.
  
  
  RESULTS
  The lenses did have a brown tint and they did meet the North American and European occupational sunglass transmittance requirements for roadway traffic signal lights. However, they did not meet the Australian occupational requirements because the red signal visibility factor was too high. Calculations using typical railroad wayside signal lights showed that the lenses would shift the yellow signal chromaticity coordinates beyond the boundaries for the railway yellow signals and toward the red end of the International Commission on Illumination chromaticity diagram, confirming the employees' reports.
  
  
  CONCLUSIONS
  Although the lenses met the North American and European sunglass transmittance requirements for traffic signal lights, the results showed that these standards are inappropriate for the railroad environment because the yellow wayside signal lights are redder and smaller in angular size than typical North American and European traffic lights. Some suggestions on a modified transmittance requirement are given to avoid this problem in the future.
authors.affiliation: University of Waterloo, School of Optometry, Waterloo, Ontario, Canada. jhovis@uwaterloo.ca
authors.forename: Jeffery K
authors.initials: JK
authors.lastname: Hovis
mesh_terms: D002170:Canada; D003116:Color; D005135:Eye Protective Devices / Q000592:standards*; D006801:Humans; D011890:Railroads; D013053:Spectrophotometry; D013472:Sunlight