 By decreasing the wavelength, increasing the numerical aperture from 0.60 to 0.85, and making the cover layer thinner to avoid unwanted optical effects, designers can cause the laser beam to focus on a smaller spot, which effectively allows more information to be stored in the same area.For a Blu-ray Disc, the spot size is 580 nm.This allows a reduction of the pit size from 400 nm for DVD to 150 nm for Blu-ray Disc, and of the track pitch from 740 nm to 320 nm.