  We present a scenario for the formation of disks which explains not only the
properties of normal galaxies, but the properties of the population of low
surface brightness galaxies (LSBs) as well. We use a gravitationally
self-consistent model for disk collapse to calculate the observable properties
of disk galaxies as a function of mass and angular momentum of the initial
protogalaxy. The model naturally produces smooth, asymptotically flat rotation
curves, exponential surface brightness profiles over many disk scale lengths,
the Tully-Fisher relation as a function of surface brightness, the observed
distribution of scale lengths and surface brightnesses, and the variation of
rotation curve shapes. In the model, low mass and/or high angular momentum
halos naturally form low surface brightness disks. Theoretical and numerical
calculations suggest galaxy halos should form with a wide range of mass and
angular momenta, and thus, the disks which form within these halos should have
a wide range of surface brightnesses and scale lengths. We use the formalism to
calculate the expected change in the observed luminosity function (LF) and
luminosity density as a function of limiting surface brightness. Current
measurements of the LF may by off by factors of 2 at L*. [SHORTENED]
