Abstract
This report examines published data on the luminous intensity necessary for the detection of a signal on the line of sight. The effects on signal intensity of signal size, colour, surround screens, background luminance, day-night use, driver age, anomalous colour vision and tinted glass are discussed. Using ten conclusions the on-axis intensity for the light distribution for a traffic signal may be deduced for any site conditions. High intensity requirements can result from this procedure and care must be taken to minimise signal range.