  The transverse size of q q-bar fluctuations of a longitudinally polarized
photon is reduced relative to the transerve size of q q-bar fluctuation of a
transversely polarized photon. This implies a model-independent prediction of
the ratio R(W2,Q2)=sigma_L/sigma_T=0.375, or, equivalently, F_L/F_2=0.27, for
x=Q2/W2<<1 and Q2 sufficiently large, while R(W2,Q2)=0.50, if this effect is
ignored. Experimental data from HERA confirm the transverse-size reduction.
