In physics, a Bragg plane is a plane in reciprocal space which bisects a reciprocal lattice vector, ${\displaystyle \scriptstyle \mathbf {K} }$, at right angles. The Bragg plane is defined as part of the Von Laue condition for diffraction peaks in x-ray diffraction crystallography.

Considering the adjacent diagram, the arriving x-ray plane wave is defined by:

Where ${\displaystyle \scriptstyle \mathbf {k} }$ is the incident wave vector given by:

where ${\displaystyle \scriptstyle \lambda }$ is the wavelength of the incident photon. While the Bragg formulation assumes a unique choice of direct lattice planes and specular reflection of the incident X-rays, the Von Laue formula only assumes monochromatic light and that each scattering center acts as a source of secondary wavelets as described by the Huygens principle. Each scattered wave contributes to a new plane wave given by:

The condition for constructive interference in the ${\displaystyle \scriptstyle {\hat {n}}^{\prime }}$ direction is that the path difference between the photons is an integer multiple (m) of their wavelength. We know then that for constructive interference we have:

where ${\displaystyle \scriptstyle m~\in ~\mathbb {Z} }$. Multiplying the above by ${\displaystyle \scriptstyle {\frac {2\pi }{\lambda }}}$ we formulate the condition in terms of the wave vectors, ${\displaystyle \scriptstyle \mathbf {k} }$ and ${\displaystyle \scriptstyle \mathbf {k^{\prime }} }$:

Now consider that a crystal is an array of scattering centres, each at a point in the Bravais lattice. We can set one of the scattering centres as the origin of an array. Since the lattice points are displaced by the Bravais lattice vectors, ${\displaystyle \scriptstyle \mathbf {R} }$, scattered waves interfere constructively when the above condition holds simultaneously for all values of ${\displaystyle \scriptstyle \mathbf {R} }$ which are Bravais lattice vectors, the condition then becomes:

An equivalent statement (see mathematical description of the reciprocal lattice) is to say that: