A bandwidth meter method and apparatus for measuring the bandwidth of a spectrum of light emitted from a laser input to the bandwidth meter is disclosed, which may comprise an optical bandwidth monitor providing a first output representative of a first parameter which is indicative of the bandwidth of the light emitted from the laser and a second output representative of a second parameter which is indicative of the bandwidth of the light emitted from the laser; and, an actual bandwidth calculation apparatus utilizing the first output and the second output as part of a multivarible equation employing predetermined calibration variables specific to the optical bandwidth monitor, to calculate an actual bandwidth parameter. The apparatus and method may be implemented in a laser lithography light source and/or in an integrated circuit lithography tool.