  We compute the production rate of photons in the ionizing Lyman continua
(LyC) of H I (lambda < 912 A), He I (lambda < 504 A), and He II (lambda < 228
A) using recent stellar evolutionary tracks coupled to a grid of non-LTE,
line-blanketed (WM-basic) model atmospheres. The median LyC production
efficiency is Q_LyC = (6+/-2)x10^60 LyC photons per Msun of star formation
(range [3.1-9.4]x10^60) corresponding to a revised calibration of
10^{53.3+/-0.2} photons/s per Msun/yr. Efficiencies in the helium continua are
Q_HeI ~ 10^60 photons/Msun and Q_HeII ~ 10^56 photons/Msun at solar metallicity
and larger at low metallicity. The critical star formation rate needed to
maintain reionization against recombinations at z = 7 is rho_SFR = (0.012
Msun/yr/Mpc^3) [(1+z)/8]^3 [(C_H /3) (0.2/ f_esc) for fiducial values of IGM
clumping factor C_H = 3 and LyC escape fraction f_esc = 0.2. The boost in LyC
production efficiency is an important ingredient, together with metallicity,
C_H, and f_esc, in assessing whether IGM reionization was complete by z ~ 7.
Monte-Carlo sampled spectra of coeval starbursts during the first 5 Myr have
intrinsic flux ratios of F(1500)/F(900) = 0.4-0.5 and F(912^-)/F(912^+) =
0.4-0.7 in the far-UV (1500A), the LyC (900A), and at the Lyman edge (912A).
These ratios can be used to calibrate the LyC escape fractions in starbursts.
