The formula for the brighter patches resulting from constructive interference and darker patches resulting from destructive interference in a diffraction grating is:
dsin(θ) = nλ
Here, d is the spacing between the grating, θ is the angle of light, n is the fringe order and λ is the wavelength. N has integer values only.
Destructive interference occurs between the fringes, so the formula for destructive interference becomes:
dsin(θ) = (n+1/2)λ, where n is again an integer.
