A lamp, comprising: a half mirror having an upper surface and a lower surface, and configured to reflect a part of light incident to the lower surface and another part to be discharged outside; a reflector disposed below the half mirror in a manner of facing the lower surface of the half mirror; an electrochromic layer disposed between the half mirror and the reflector and covering the reflector; a light source unit emitting light between the half mirror and the reflector; and a controller applying a current or voltage to the electrochromic layer, wherein the electrochromic layer is configured to have light transmittance that changes as a current or voltage is applied, wherein at least a part of the electrochromic layer is converted from one of a first state having a first transmittance and a second state having a second transmittance that is higher than the first transmittance to another, wherein the lamp further comprises a plurality of auxiliary light sources disposed between the electrochromic layer and the reflector, wherein the auxiliary light sources are arranged in a line along one direction, wherein in a state that at least some of the auxiliary light sources are all turned off, wherein the controller sequentially turns on the at least some of the auxiliary light sources in one direction until the at least some of the auxiliary light sources are all turned on, or, wherein the electrochromic layer is provided with a plurality of regions (330a-330e) electrically isolated from one another, wherein each of the plurality of auxiliary light sources is disposed to overlap one of the plurality of regions (330a-330e). a half mirror having an upper surface and a lower surface, and configured to reflect a part of light incident to the lower surface and another part to be discharged outside; a reflector disposed below the half mirror in a manner of facing the lower surface of the half mirror; an electrochromic layer disposed between the half mirror and the reflector and covering the reflector; a light source unit emitting light between the half mirror and the reflector; and a controller applying a current or voltage to the electrochromic layer, wherein the electrochromic layer is configured to have light transmittance that changes as a current or voltage is applied, wherein at least a part of the electrochromic layer is converted from one of a first state having a first transmittance and a second state having a second transmittance that is higher than the first transmittance to another, wherein the lamp further comprises a plurality of auxiliary light sources disposed between the electrochromic layer and the reflector, wherein the auxiliary light sources are arranged in a line along one direction, wherein in a state that at least some of the auxiliary light sources are all turned off, wherein the controller sequentially turns on the at least some of the auxiliary light sources in one direction until the at least some of the auxiliary light sources are all turned on, or, wherein the electrochromic layer is provided with a plurality of regions (330a-330e) electrically isolated from one another, wherein each of the plurality of auxiliary light sources is disposed to overlap one of the plurality of regions (330a-330e).