  We have measured the bar lengths and widths of 125 barred galaxies observed
with CCDs. The dependence of bar strength (identified with bar axis ratio) on
morphological type, nuclear activity, central and mid-bar surface brightness is
investigated.
  The properties of the bars are best explained if the sample is divided into
early- (< SBbc) and late-type galaxies, and into active (starburst, Seyfert or
LINER) and normal galaxies. We find that galaxies with very long bars are
mostly active and that normal late-type galaxies have a distinct behavior from
the three other groups of galaxies. We confirm earlier findings that active
late-type galaxies tend to have both stronger and longer bars than normal ones.
An important result of this paper is that early-type galaxies do not share this
behavior : they all tend to have strong bars, whether they are active or not.
We also find correlations between bar strength and relative surface brightness
in the middle and at the edge of the bar, which are not followed by normal
late-type galaxies.
  These results are interpreted in the light of recent numerical simulations
and paradigms about galaxy evolution. They suggest that normal late-type
galaxies represent the first stage of galaxy evolution, and that bars in early-
and late-type galaxies do not have the same properties because they have a
different origin.
