Abstract: The invention relates to a device and a method for spectroscopic measurement of the spectrum of a light beam. According to the method, one detects the dispersed light fluxes of said beam on an imaging device comprising a matrix of photodetectors (23) with active columns (11). According to the invention, said imaging device (10) is directed so that one wavelength is allocated to a line (27) of photodetectors (12). One determines for each light flux (i=1, 2, . . . , n) the exposure time ?i necessary to measure a maximal intensity Imax and the sub-matrix Mi (13, 24-26) of photodetectors (12) associated with said light fluxes. One allocates to the sub-matrix Mi (13, 24-26) of photodetectors an exposure time ?!i so that ??i is the largest integer divider of the total integration time T smaller than ?i. During the integration time T of said spectrum, one measures and one resets, at each time ??i with i=(1, 2, . . .