Safety and comfort while driving at night depend on the visual detection of objects, which is based on contrast. The performance of this visual task is related to the relative contrast sensitivity of the lighting system provided, which is a function of roadway or background luminance of disability glare from luminaires by specifying a minimum value of effective relative contrast sensitivity for a particular road class is proposed. A simple formula has been derived for the effective relative contrast sensitivity of a lighting system by using curve-fitted, standardized data. Glare control by limiting the relative contrast sensitivity can be achieved by a permissible glare formula or a diagram. The method is demonstrated by examples. Relative-contrast-sensitivity glare control can also be combined with a method that is based on limiting the threshold increment of a critical-size object. The relative-contrast-sensitivity method and the visibility-index method both use the same concept of contrast-sensitivity change with glare.