 Interference fringe spacing

The distance between adjacent bright interference fringes, or between adjacent dark interference fringes, measured along a specified direction. For the symmetric crossing plane waves in wave interference, measured along $x$, $\Lambda =\lambda /(2\sin \theta )$. Bright-to-dark separation is $\Lambda /2$. As $\theta$ tends to zero the spacing diverges; at $\theta =0$ the phase difference is spatially constant and there are no periodic bands.