  Using a simple method to interpret the luminosity function of Ly-alpha
emitters, we explore properties of Ly-alpha emitters from 5.7 < z < 8.8 with
various assumptions about metallicity and stellar mass spectra. We constrain a
mass-to-'observed' light ratio, M_h/L_band. For narrow-band surveys, L_band is
simply related to the intrinsic Ly-alpha luminosity with a survival fraction of
Ly-alpha photons, alpha_esc. The mass-to-'bolometric light', M_h/L_bol, can
also be deduced, once the metallicity and stellar mass spectrum are given. The
inferred M_h/L_bol is more sensitive to metallicity than to the mass spectrum.
We find the following constraints on a mass-to-light ratio of Ly-alpha emitters
from 5.7 < z < 7: (M_h/L_bol)(alpha_{esc}epsilon^{1/gamma})^{-1}=21-38, 14-26,
and 9-17 for Z=0, 1/50, and 1 Z_sun, respectively, where epsilon is the 'duty
cycle' of Ly-alpha emitters, and gamma ~ 2 is a local slope of the cumulative
luminosity function. Only weak lower limits are obtained for z=8.8. Therefore,
Ly-alpha emitters are consistent with either starburst galaxies M_h/L_bol ~
0.1-1 with a smaller Ly-alpha survival fraction, alpha_{esc}epsilon^{1/gamma}
~0.01-0.05, or normal populations (M_h/L_bol ~ 10) if a good fraction of
Ly-alpha photons survived, alpha_{esc}epsilon^{1/gamma} ~ 0.5-1. We find no
evidence for the end of reionization in the luminosity functions of Ly-alpha
emitters discovered in the current Ly-alpha surveys, including recent discovery
of one Ly-alpha emitter at z=7. The data are consistent with no evolution of
intrinsic properties of Ly-alpha emitters or neutral fraction in the
intergalactic medium up to z=7. No detection of sources at z=8.8 does not yield
a significant constraint yet. We also show that the lack of detection at z=8.8
does not rule out the high-z galaxies being the origin of the excess NIRB.
