  The current sparse wavelength range coverage of exoplanet direct imaging
observations, and the fact that models are defined using a finite wavelength
range, lead both to uncertainties on effective temperature determination.We
study these effects using black-bodies and atmospheric models and we detail how
to infer this parameter. Through highlighting the key wavelength coverage that
allows for a more accurate representation of the effective temperature, our
analysis can be used to mitigate or manage extra uncertainties being added in
the analysis from the models. We find that the wavelength range coverage will
soon no longer be a problem. An effective temperature computed by integrating
the spectroscopic observations of the James Webb Space Telescope (JWST) will
give uncertainties similar to, or better than, the current state-of-the-art,
which is to fit models to data. Accurately calculating the effective
temperature will help to improve current modelling approaches. Obtaining an
independent and precise estimation of this crucial parameter will help the
benchmarking process to identify the best practice to model exoplanet
atmospheres.
