In Young's double slit experiment, fringes of width \(\beta\) are produced on the screen kept at a distance of 1 m from the slit. When the screen is moved away by \(5 \times 10^{-2}\) m, fringe width changes by \(3 \times 10^{-5}\) m. The separation between the slits is \(1 \times 10^{-3}\) m. The wavelength of light used is .................... nm.