the media it is typically preferred that the light changeable material layer be applied at a thickness that is thin enough to allow transmission of light to adequately read the underlying data upon initial sampling while being dense enough to provide adequate change such as light emission upon oversampling with the same reader for many applications a film thickness of from 50 to 160 nm is found useful for most cds the film thickness is in the range of from about 70 nm to about 130 nm while for most dvd the film thickness is preferably in the range of from about 50 nm to about 160 nm as would be understood by one of ordinary skill in the art the persistence of the activated state of the light changeable material such as a light sensitive material i e the length of time the material is in the activated state versus initial state and the delay in the conversion of the initial state to the activated state i e the length of time it takes the material to enter the activated state from the initial state are important to permit the proper read of the underlying data and for causing a change in the data read upon re sampling given a pit size of 8 u03bcm and a typical rotational speed of 1 2 m sec in a cd rom the preferred delay in a cd is a minimum of about 6 85 u00d7 10 u2212 7 seconds given a pit size of 0 4 u03bcm and a rotational speed of about 3 5 m sec in a dvd the preferred delay in a dvd is a minimum of about 1.