  Kepler produces a large amount of data used for asteroseismological analyses,
particularly of solar-like stars and red giants. The mode amplitudes observed
in the Kepler spectral band have to be converted into bolometric amplitudes to
be compared to models. We give a simple bolometric correction for the
amplitudes of radial modes observed with Kepler, as well as the relative
visibilities of non-radial modes. We numerically compute the bolometric
correction c_{K-bol} and mode visibilities for different effective temperatures
Teff within the range 4000-7500 K, using a similar approach to a recent one
from the literature (Michel et al. 2009, A&A 495, 979). We derive a law for the
correction to bolometric values: c_{K-bol} = 1 + a_1 (Teff-To) + a_2
(Teff-To)^2, with To = 5934 K, a_1 = 1.349e-4 K^{-1}, and a_2 = -3.120e-9
K^{-2} or, alternatively, as the power law c_{K-bol} = (Teff/To)^alpha with
alpha = 0.80. We give tabulated values for the mode visibilities based on
limb-darkening (LD), computed from ATLAS9 model atmospheres for Teff in
[4000,7500] K, log g in [2.5,4.5], and [M/H] in [-1.0,+1.0]. We show that using
LD profiles already integrated over the spectral band provides quick and good
approximations for visibilities. We point out the limits of these classical
visibility estimations.
