The signature of two different scales of solar granulation in the power spectrum of disk integrated irradiance time series is presented. The fitted timescales for granulation (τGR1≈ 237~s and τGR2≈ 62~s) are in good agreement with the characteristic lifetimes derived from recent image time series of the Sun's surface (Del Moro 2004); and probably linked to magnetic chromospheric structures such as bright points (Harvey et al. 1993).