  Far-ultraviolet (FUV) radiation plays an important role in determining
chemical abundances in protoplanetary disks. HI Lyman alpha is suspected to be
the dominant component of the FUV emission from Classical T Tauri Stars
(CTTSs), but is difficult to measure directly due to circumstellar and
interstellar HI absorption. To better characterize the intrinsic Lyman alpha
radiation, we present FUV spectra of 14 CTTSs taken with the Hubble Space
Telescope COS and STIS instruments. H2 fluorescence, commonly seen in the
spectra of CTTSs, is excited by Lyman alpha photons, providing an indirect
measure of the Lyman alpha flux incident upon the warm disk surface. We use
observed H2 progression fluxes to reconstruct the CTTS Lyman alpha profiles.
The Lyman alpha flux correlates with total measured FUV flux, in agreement with
an accretion-related source of FUV emission. With a geometry-independent
analysis, we confirm that in accreting T Tauri systems Lyman alpha radiation
dominates the FUV flux (~1150 - 1700 Angstroms). In the systems surveyed this
one line comprises 70 - 90 % of the total FUV flux.
