  Solar flares radiates energy at all wavelengths, but the spectral
distribution of this energy is still poorly known. White-light continuum
emission is sometimes observed and the flares are then termed "white-light
flares" (WLF). In this paper, we investigate if all flares are white-light
flares and how is the radiated energy spectrally distributed. We perform a
superposed epoch analysis of spectral and total irradiance measurements
obtained since 1996 by the SOHO and GOES spacecrafts at various wavelength,
from Soft X-ray to the visible domain. The long-term record of solar irradiance
and excellent duty cycle of the measurements allow us to detect a signal in
visible irradiance even for moderate (C-class) flares, mainly during the
impulsive phase. We identify this signal as continuum emission emitted by
white-light flares, and find that it is consistent with a blackbody emission at
~9000K. We estimate for several sets of flares the contribution of the WL
continuum and find it to be of ~70% of the total radiated energy. We re-analyse
the X17 flare that occurred on 28 October 2003 and find similar results. This
paper brings evidence that all flares are white-light flares and that the
white-light continuum is the main contributor to the total radiated energy;
this continuum is consistent with blackbody spectrum at ~9000K. These
observational results are important in order to understand the physical
mechanisms during flares and open the way to a possible contribution of flares
to TSI variations.
