Spectral resolution is limited optically by the grating properties. The limit of resolution is determined by the Rayleigh criterion as applied to the diffraction maxima, i.e., two wavelengths are just resolved when the maximum of one lies at the first minimum of the other. This resolution is quantified by the grating resolvance:

$$ \Delta\lambda_{\text{optic}} = \frac{\lambda}{R} $$

Where:

• $\Delta\lambda_{\text{optic}}$ [m]: Optically-limited spectral resolution.
• $\lambda$ [m]: Wavelength of interest.
• $R$: Resolvance