white_light step has two step-specific arguments to allow
wavelength limits during the flux summation. One or both may be specified.
min_wavelengthis specified, the
white_lightstep will sum from the specified wavelength to either a specified
max_wavelengthor the end of the flux array.
max_wavelengthis specified, the
white_lightstep will sum from either a specified
min_wavelengthor the beginning of the flux array to the specified wavelength.