At the solar surface the magnetic field is bundled into discrete elements o
f concentrated flux, often referred to as magnetic flux tubes, which cover
only a small fraction of the solar surface. Flux tubes span a whole spectru
m of sizes, ranging from sunspots to features well below the best currently
obtainable spatial resolution.
Whereas sunspots have been well studied, our knowledge of the true brightne
ss of small-scale magnetic features is hampered by the insufficient spatial
resolution of the observations. A better understanding of the thermal and
magnetic properties of these small-scale features, however, is crucial fur
an understanding of (climate-relevant) long-term solar irradiance variation
s.