Light containing two spectral lines of unknown wavelengths \(\lambda_1\) and \(\lambda_2\) (where \(\lambda_1 > \lambda_2\)) is incident normally on a diffraction grating with line spacing \(d\). A detector observes that the \(m\)th-order principal maximum of \(\lambda_1\) occurs at the exact same diffraction angle \(\theta\) as the \((m+1)\)th-order principal maximum of \(\lambda_2\). Which of the following expressions represents the difference in wavelengths, \(\Delta \lambda = \lambda_1 - \lambda_2\)?