The best-fitting 2-dimensional plane within the 3-dimensional space of spiral galaxy disk observables ( rotational velocity v _ { rot } , central disk surface brightness \mu _ { 0 } = -2.5 \log I _ { 0 } , and disk scale-length h ) has been constructed . Applying a three-dimensional bisector method of regression analysis to a sample of \sim 100 spiral galaxy disks that span more than four mag arcsec ^ { -2 } in central disk surface brightness yields v _ { rot } \propto I _ { 0 } ^ { 0.50 \pm 0.05 } h ^ { 0.77 \pm 0.07 } ( B -band ) and v _ { rot } \propto I _ { 0 } ^ { 0.43 \pm 0.04 } h ^ { 0.69 \pm 0.07 } ( R -band ) . Contrary to popular belief , these results suggest that in the B -band , the dynamical mass-to-light ratio ( within 4 disk scale-lengths ) is largely independent of surface brightness , varying as I _ { 0 } ^ { 0.00 \pm 0.10 } h ^ { 0.54 \pm 0.14 } . Consistent results were obtained when the expanse of the analysis was truncated by excluding the low surface brightness galaxies . Previous claims that M / L _ { B } varies with I _ { 0 } ^ { -1 / 2 } are shown to be misleading and/or due to galaxy selection effects . Not all low-surface-brightness disk galaxies are dark matter dominated . The situation is however different in the near-infrared where L _ { K ^ { \prime } } \propto v ^ { 4 } and M / L _ { K ^ { \prime } } is shown to vary as I _ { 0 } ^ { -1 / 2 } . Theoretical studies of spiral galaxy disks should not assume a constant M / L ratio within any given passband . The B -band dynamical mass-to-light ratio ( within 4 disk scale-lengths ) has no obvious correlation with ( B - R ) disk colour , while in the K ^ { \prime } -band it varies as -1.25 \pm 0.28 ( B - R ) . Combining the present observational data with recent galaxy model predictions implies that the logarithm of the stellar-to-dynamical mass ratio is not a constant value , but increases as disks become redder , varying as 1.70 \pm 0.28 ( B - R ) .