  Barnes-Evans type relations provide an empirical relationship between the
surface brightness of stars and their color. They are widely used for measuring
the distances to stars of known radii, as the Roche-lobe filling secondaries in
cataclysmic variables (CVs). The calibration of the surface brightness of field
dwarfs of near-solar metalicity with spectral types A0 to L8 covers all
secondary spectral types detectable in CVs and related objects and will aid in
the measurement of their distances. The calibrations are based on the radii of
field dwarfs measured by the Infrared Flux Method and by interferometry.
Published photometry is used and homogenized to the Cousins Rc and Ic and the
CIT JHK photometric systems. The narrow band surface brightness at 7500A is
based on our own and published spectrophotometry. Care is taken to select the
dwarfs for near-solar metalicity, appropriate to CVs, and to avoid errors
caused by unrecognized binarity. Relations are provided for the surface
brightness in V, Rc, Ic, J, H, K and in a narrow band at 7500A as functions of
V-K and of spectral type. The method is tested with selected CVs for which
independent information on their distances is available. The observed spread in
the radii of early M-dwarfs of given mass or luminosity and its influence on
the distance measurements of CVs is discussed. As long as accurate
trigonometric parallaxes are not routinely available for a large number of CVs,
the surface brightness method remains a reliable means of determining distances
to CVs in which a spectral signature of the secondary star can be discerned.
