Knowledge of the solar irradiance background is of great importance to solar and stellar physics. In particular, its contribution to the solar oscillations power spectrum is highly relevant as it represents the ultimate limit to the sensitivity of solar oscillations' observations. An analysis of the power spectra of the solar photometric data coming from four different instruments - two space-borne (ACRIM and IPHIR) and two earth-based instruments (SLOT and LOI-T) - has been performed to obtain the upper limit to the solar irradiance background's spectrum. These observations have been compared to a numerical model computed for the non-coherent solar surface phenomena, namely granulation, mesogranulation and supergranulation. There is an overall good agreement between the general trend of the model and the observed data.