  The goal of this paper is to characterise the light variation properties of
Mira variables in the Small Magellanic Cloud. We have investigated a combined
optical and near infrared multi-epoch dataset of Mira variables based on our
monitoring data obtained over 15 years. Bolometric correction relations are
formulated for various near-infrared colours. We find that the same bolometric
correction equation holds for both the bolometricly brightest and faintest
pulsation phases. Period-bolometric magnitude relations and period-colour
relations were derived using time-averaged values. Phase lags between
bolometric phase and optical and near-infrared phases were detected from the
O-rich (the surface C/O number ratio is below unity) Mira variables, while no
significant systematic lags were observed in most of the C-rich (the C/O ratio
is over unity) ones. Some Miras show colour phase inversions, e.g., $H-K_{\rm
s}$ at its bluest while $J-H$ and $J-K_{\rm s}$ are at their reddest values at
about the bolometricly brightest phase. Their occurrence conditions were
studied but no clear direct or indirect trigger was found. A large NIR colour
change unassociated with stellar pulsation was observed in Miras with long
secondary periods, and its possible explanation is described.
