From a diameter-limited sample of 86 ‘ face-on ’ spiral galaxies , the bulge-to-disk size and luminosity ratios , and other quantitative measurements for the prominence of the bulge are derived .
The bulge and disk parameters have been estimated using a seeing convolved Sérsic r ^ { 1 / n } bulge and a seeing convolved exponential disk which were fitted to the optical ( B,R , and I ) and near-infrared ( K ) galaxy light profiles .
In general , early-type spiral galaxy bulges have Sérsic values of n > 1 , and late-type spiral galaxy bulges have values of n < 1 .
Use of the exponential ( n = 1 ) bulge model is shown to restrict the range of r _ { e } / h and B / D values by more than a factor of 2 .
Application of the r ^ { 1 / n } bulge models results in a larger mean r _ { e } / h ratio for the early-type spiral galaxies than the late-type spiral galaxies .
Although , this result is shown not to be statistically significant .
The mean B / D luminosity ratio is , however , significantly larger ( > 3 \sigma ) for the early-type spirals than the late-type spirals .

Two new parameters are introduced to measure the prominence of the bulge .
The first is the difference between the central surface brightness of the galaxy and the surface brightness where the bulge and disk contribute equally .
The other test uses the radius where the contribution from the disk and bulge light is equal – normalised for the effect of intrinsically different galaxy sizes .
Both of these parameters reveale that the early-type spiral galaxies ‘ appear ’ to have significantly ( > 2 \sigma in all passbands ) bigger and brighter bulges than late-type spiral galaxies .
This apparent contradiction with the r _ { e } / h values can be explained with an iceberg-like scenario , in which the bulges in late-type spiral galaxies are relatively submerged in their disk .
This can be achieved by varying the relative bulge/disk stellar density while maintaining the same effective bulge-to-disk size ratio .

The B / D luminosity ratio and the concentration index C _ { 31 } are , in agreement with past studies , positively correlated and decrease as one moves along the spiral Hubble sequence towards later galaxy types .
Although for galaxies with large extended bulges , the concentration index no longer traces the B / D luminosity ratio in a one-to-one fashion .
A strong ( Spearman ’ s r _ { s } =0.80 ) and highly significant positive correlation exists between the shape , n , of the bulge light profile and the bulge-to-disk luminosity ratio .

The absolute bulge magnitude – \log n diagram is used as a diagnostic tool for comparative studies with dwarf elliptical and ordinary elliptical galaxies .
At least in the B -band , these objects occupy distinctly different regions of this parameter space .
While the dwarf ellipticals appear to be the faint extension to the brighter elliptical galaxies , the bulges of spiral galaxies are not ; for a given luminosity they have a noticeably smaller shape parameter and hence a more dramatically declining stellar density profile at larger radii .