  We determine the work functions of the iron arsenic compounds $A$Fe$_2$As$_2$
($A=\mathrm{Ca, Ba, Cs}$) using photoemission spectroscopy to be 2.7 eV for
CaFe$_2$As$_2$, 1.8 eV for BaFe$_2$As$_2$, and 1.3 eV for CsFe$_2$As$_2$. The
work functions of these 122 iron-based superconductors track those of the
elementary metal $A$ but are substantially smaller. The most likely explanation
of this observation is that the cleaving surface exposes only half an
$A$-layer. The low work function and good photoemission cross section of
BaFe$_2$As$_2$ and CsFe$_2$As$_2$ enable photoemission even from a common white
LED light.
