reference will now be made in detail to an embodiment of the present invention , examples of which is illustrated in the accompanying drawings . fig5 is a view illustrating a v - t ( voltage - transmittance ) graph of an lcd device according to the embodiment of the present invention and a v - t graph of an lcd device of the related art . the lcd device according to the embodiment may include a liquid crystal panel and a driving circuit similar to those of the related art . explanations of parts similar to parts of the related art may be omitted . the lcd device according to the embodiment may be operated in a normally white mode . the lcd device according to the embodiment may be operated in an over - driving method . the lcd device according to the embodiment may be operated in a tn ( twisted nematic ) mode or an ecb ( electrical controlled birefringence ) mode . the tn mode lcd device includes a tn mode liquid crystal material interposed between first and second substrates of the lcd device , and first and second alignment layers on inner surfaces of the first and second substrates , respectively . the first alignment layer has a first rubbing direction perpendicular to a second rubbing direction of the second alignment layer . accordingly , tn mode liquid crystal molecules are arranged to be twisted with 90 degrees angle along a direction perpendicular to a plane of the substrates when an electric field between the two substrates is not applied , and arrangement of the tn mode liquid crystal molecules are changed in accordance with the electric filed applied between the two substrates . the ecb mode lcd device includes an ecb mode liquid crystal material interposed between first and second substrates of the lcd device , and first and second alignment layers on inner surfaces of the first and second substrates , respectively . the first alignment layer has a first rubbing direction parallel to a second rubbing direction of the second alignment layer . for example , the first and second rubbing directions are the same direction or opposite direction . accordingly , ecb mode liquid crystal molecules are arranged according to the rubbing directions of the first and second alignment layers , and arrangement of the ecb mode liquid crystal molecules are changed in accordance with the electric filed applied between the two substrates . the lcd device according to the embodiment may be operated in an over - driving method even when white is displayed , differently from the related art . referring to fig5 , while the related art lcd device is operated according to a first graph g 1 , the lcd device according to the embodiment is operated according to a second graph g 2 . the second graph g 2 shows that white is displayed at a first data voltage v 1 having a level higher than 0v which is to display white as shown in the first graph g 1 of the related art lcd device , and black is displayed at a second data voltage v 2 . to set the first voltage v 1 having a level higher than 0v , the lcd device according to the embodiment may have a retardation value of a liquid crystal material more than that of the related art lcd device . the related art tn mode lcd device has a retardation value of a tn mode liquid crystal material of 480 nm , and the related art ecb mode lcd device has a retardation value of an ecb mode liquid crystal material of 275 nm . the retardation value is determined by a expression , r = δn * d ( r is a retardation value , δn is a refraction index difference of an extra - ordinary refraction index ( ne ) and an ordinary refraction index ( no ) of a liquid crystal molecule , and d is a thickness of a liquid crystal layer ). accordingly , the tn mode lcd device according to the embodiment may have a retardation value more than 480 nm , and the ecb mode lcd device according to the embodiment may have a retardation value more than 275 nm . for example , the tn mode lcd device may have a retardation value within a range of about 104 % to 130 % of 480 nm i . e ., about 500 nm to 624 nm , and the ecb mode lcd device may have a retardation value within a range of about 104 % to 130 % of 275 nm i . e ., about 286 nm to 357 nm . to have this retardation value , at least one of the refraction index difference and the thickness of the liquid crystal layer may be adjusted . the second graph g 2 of fig5 is a graph when the tn mode lcd device has a retardation value of about 600 nm . as described above , by adjusting the retardation value appropriately , the lcd device has the second graph g 2 to perform an over - driving method even when displaying white . fig6 is a view illustrating a method of driving an lcd device according to the embodiment of the present invention . referring to fig5 and 6 , black is displayed at a pixel in the previous frame by a second data voltage v 2 . to display white in the present frame , a data voltage , which has a level within a range of equal to or higher than 0v and lower than a level of a first data voltage v 1 , is applied first for a first over - driving time out of a data - applying time . assuming that the data voltage is 0v . liquid crystal molecules rotates faster when 0v is applied than when the first voltage as an original data voltage required to display white is applied , and thus state of the liquid crystal molecules to display white having the first transmittance t 1 is reached faster . if 0v were still applied after the first over - driving time , the liquid crystal molecules would finally have a state to have the second transmittance t 2 , according to a fourth graph g 4 in fig6 , less than the first transmittance t 1 for white . the fourth graph g 4 shows variation of a transmittance when 0v is still applied , based upon the first graph g 1 . accordingly , after the first over - driving time i . e ., the first transmittance t 1 is reached by applying 0v , the first data voltage v 1 is applied for the rest time out of the data - applying time , and thus the first transmittance t 1 is maintained as shown in a third graph g 3 of fig6 . as described above , by setting the data voltage for white to have a level higher 0v , the over - driving can be performed to display white in a manner that the data voltage having a level within a range of equal to or higher than 0v and lower than the level of the data voltage to display white is applied first for the first over - driving time . therefore , a response time for white can be reduced to a time td less than the response time ( tb of fig4 ) of the related art . after the data - applying time , the first data voltage v 1 is stored in the pixel and the first transmittance t 1 is maintained in the present frame . then , to display a gray level darker than white , for example , black in the next frame , a third data voltage v 3 is applied first for a second over - driving time out of a data - applying time . the third data voltage v 3 has a level higher than a level of the second data voltage v 2 as an original data voltage required to display black , to perform an over - driving for black . accordingly , liquid crystal molecules rotates faster when the third data voltage v 3 is applied than the second voltage v 2 is applied , and thus state of the liquid crystal molecules to display black having a third transmittance t 3 is reached faster . after the second over - driving time i . e ., the third transmittance t 3 is reached by applying the third data voltage v 3 , the second data voltage v 2 is applied for the rest time out of the data - applying time , and thus the third transmittance t 3 is maintained . as described in the embodiment of the present invention , the lcd device can be operated in the over - driving method not only when displaying gray levels darker than white but also when displaying black by setting the white data voltage to have a level higher 0v . accordingly , the lcd device can have fast response times for all of gray levels , and display quality can be improved . it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention . thus , it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents .