Patent ID: 7569316

Claim:
An image forming medium, comprising a substrate; and an imaging layer coated on or impregnated into said substrate, wherein the imaging layer comprises an imaging composition comprising a photochromic or photochromic-thermochromic material dissolved or dispersed in a solvent or polymeric binder; wherein the photochromic or photothermochromic material is selected so that: the imaging composition is imageable by light of a first wavelength and erasable in a short time period by a combination of heat and light of a second wavelength such that the simultaneous erase using a fixed amount of heat energy and light energy of the second wavelength leads to a higher degree of erase than if the fixed quantity of heat energy and light energy of the second wavelength were applied sequentially; wherein the short time period is the time period for the maximum absorbance of the imaging composition in the region 400-800 nm to be reduced from its initial absorbance to one half of the initial absorbance, in about 10 minutes or less; the image forming medium exhibits a reversible transition between a colorless and a colored state; and the imaging composition exhibits an erase enhancement factor (EF) of greater than 1, wherein: EF is equal to a half-life expected (t exp ) divided by a half-life observed (t obs ), t exp is equal to the product of t L2 and t H2 divided by the sum of T L2 and t H2 , t L2 is a half-life for erasure by light alone, and t H2 is a half-life for erasure by heat alone.