We present our measurements of the H$alpha$, [OIII], and [OII] luminosity functions as part of the Lyman Alpha Galaxies at Epoch of Reionization (LAGER) survey using our samples of 1577 $z = 0.47$ H$alpha$-, 3933 $z = 0.93$ [OIII]-, and 5367 $z = 1.59$ [OII]-selected emission line galaxies in a single 3 deg$^2$ CTIO/Blanco DECam pointing of the COSMOS field. Our observations reach 5$sigma$ depths of $8.2times10^{-18}$ erg s$^{-1}$ cm$^{-2}$ and comoving volumes of $(1-7)times10^{5}$ Mpc$^3$ making our survey one of the deepest narrowband surveys. We measure the observed luminosity functions and find best-fits of $phi^star = 10^{-3.16pm0.09}$ Mpc$^{-3}$ and $L^star = 10^{41.72pm0.09}$ erg s$^{-1}$ for H$alpha$, $phi^star = 10^{-2.16^{+0.10}_{-0.12}}$ Mpc$^{-3}$ and $L^star = 10^{41.38^{+0.07}_{-0.06}}$ erg s$^{-1}$ for [OIII], and $phi^star = 10^{-1.97^{+0.07}_{-0.07}}$ Mpc$^{-3}$ and $L^star = 10^{41.66pm0.03}$ erg s$^{-1}$ for [OII], with $alpha$ fixed to $-1.75$, $-1.6$, and $-1.3$, respectively. An excess of bright $> 10^{42}$ erg s$^{-1}$ [OIII] emitters is observed and may be due to AGN contamination. Dust corrections are applied assuming $A_{rm{H}alpha} = 1$ mag. We also design our own empirical rest-frame $g - r$ calibration using SDSS DR12 data, test it against our $z = 0.47$ H$alpha$ emitters with $z$COSMOS $1$D spectra, and calibrate it for $(g - r)$ between $-0.8$ and $1.3$ mag. Dust and AGN-corrected star formation rate densities (SFRDs) are measured as $log_{10}rho_{rm{SFR}}/(rm{M}_odot rm{yr}^{-1} rm{Mpc}^{-3}) = -1.63pm0.04$, $-1.07pm0.06$, and $-0.90pm0.10$ for H$alpha$, [OIII], and [OII], respectively. We find our [OIII] and [OII] samples fully trace cosmic star formation activity at their respective redshifts in comparison to multi-wavelength SFRDs, while the H$alpha$ sample traces $sim 70$ percent of the total $z = 0.47$ SFRD.
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