We present a measurement of the energy spectrum of the light mass group of
cosmic rays (protons and helium) with the High Altitude Water Cherenkov (HAWC)
Observatory in the energy interval from $10$ TeV to $200$ TeV. The spectrum
covers the energy range between direct and indirect measurements, where
precision data on the composition of cosmic rays are needed. The spectrum was
constructed by applying an unfolding technique on a proton plus helium
enriched sub-sample ($>90\%$ abundance) of cosmic ray air showers selected
from the HAWC cosmic-ray data. The subset contains $3.8 \times 10^{9}$ air
shower events with primary energies in the interval $1$ TeV to $300$ TeV
and zenith angles less than $16.7$ degrees. Mass selection was performed
using an analysis of the lateral age parameter of air shower events, based
on both CORSIKA/QGSJET-II-03 simulations and event-by-event measurements
on the lateral structure of the shower front and the primary energy of
the showers.