Diffraction grating: resolving power

What you are seeing: a transmission diffraction grating with $N$ slits of width $a$ and pitch $d$. The intensity pattern shows the principal maxima and the narrowing of those peaks as $N$ grows (resolving power $R = mN$). Move the two-wavelength toggle to show how a doublet is resolved when $\Delta\lambda / \lambda \gt 1/R$.