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The tidal disruption of a star by a supermassive black hole and consequent accretion can lead to a transient electromagnetic flare in multiple bands. However, the origin of the detected emission from such tidal disruption events (TDEs) remains an open question. In this talk, I will discuss the potential emission mechanisms in TDEs during accretion disk formation, implied by series of 3D radiation-hydrodynamic simulations. We find that circularization of stellar debris is not prompt. A more circularized accretion flow only forms after about one month following the initial energy dissipation, lagging behind the fallback rate peak. The circularization shocks are an important emission source rather than accretion itself. Photons produced by shocks in the inner accretion flow are reprocessed by an optically thick layer formed during circularization. The photosphere is asymmetric, leading to angular-dependent light curves. By varying the viewing angle, we can reproduce optical events that are either X-ray bright or X-ray dim. We also construct broad band broadband spectral energy distribution (SED) from simulations. At multiple epochs, the SED peaks in the extreme UV, producing optical and UV photometry that are overall consistent with observed TDEs. We also found including pre-peak UV photometry can improve blackbody temperature measurements.