  The astrophysically very interesting Li I 671 nm line has been observed with
high spatial resolution in solar granulation with the intention to diagnose
departures from local thermodynamic equilibrium (LTE) in the line formation.
The spectral feature is very weak, so this is also a test on the limits of such
observations. The observations of the Li I line and other weak lines nearby are
compared with the results of synthetic line calculations in three-dimensional
granulation simulations. The dependence of line-centre velocities on
photospheric continuum brightness is well described by the simulations. The
observed equivalent width of the Li I line show an approximately flat
dependence on continuum brightness, contrary to the theoretical LTE results.
Detailed modelling of the line radiative transfer, with an approximate
inclusion of three-dimensional effects, gives a better agreement with
observations. The match is not perfect and various interesting reasons for this
are considered. However, the possibility of systematic errors caused by the
sensitivity of the Li I equivalent width to continuum placement calls for
cautiousness in the conclusions.
