Fabry-Perot resonators or interferometers (FPI) have existed for a long time and act as light accumulators. However, their applications have been limited to the allowed resonance modes in the cavity, which are defined by the specific free-spectral range of the FPI. We show here a novel concept involving a light "capacitor" capable of accumulating light over a wide spectral range, at any given repetition frequency. This device is actually an FPI in which a high chirped mirror (chirped fiber Bragg grating or chirp multi-layer coated mirror) is added to remove the wavelength dependence of the mode resonances, enabling a single very large broad-band mode. This "modification" does not affect the amount of light which can be accumulated, i.e. it does not reduce the Q-factor of the cavity. We show here the theoretical concept of such a device and experimental results demonstrating this principle.