The Dimensional Projection Principle is formally established: every observable in the 4D interior is a projection of 5D void geometry onto the bubble wall. The velocity v=3c is derived from dimensional analysis. The 2/pi phase boundary correction is derived explicitly as the mean projection of a curved spherical surface. A new testable prediction is presented: circumferential stretch — a sin(theta)cos(theta) residual in the CMB two-point correlation at large angular scales not present in standard inflationary cosmology. Part of the Unified Light Framework series. All papers CC0.