Vehicle optical unit comprising, a housing on which a window is fixed, an incandescent lamp arranged inside a concave reflector reflecting the light produced by the lamp, the reflector and the lamp being arranged inside the optical unit so that the light produced by said lamp is reflected in the direction of the window, the reflector comprising an outer edge defining an opening of the reflector through which the light reflected by said reflector exits towards the window, the optical unit further comprises an LED fixed on an electronic card, the LED and the electronic card being arranged outside the reflector and in the optical unit, said optical unit comprising a screen wall extending from a part of the outer edge of the reflector towards the glass, along the outer edge located between the reflector and the electronic board so as to prevent air heated by the lamp to move directly towards a part of the electronic card leaving the reflector, preferably the part of the electronic card comprising the LED; the optical unit comprising a light guide illuminated by the LED, a support of the light guide holding said light guide in position, said support comprising the screen wall; the housing comprising a bottom wall arranged opposite the opening of the reflector, the electronic card being fixed to the bottom wall, the light guide having an L shape of which a first branch has one end facing the LED and a second branch which extends from the first branch at a distance from the electronic card and on the side opposite the bottom wall relative to this electronic card, the light guide support being fixed to said electronic card or to the housing; the optical unit being characterized in that the support has an L shape equivalent to the "L" shape of the light guide, comprising respectively a first branch and a second branch respectively following the first and the second branch of the light guide, means for holding the light guide, and a fixing tab extending from the second branch of the support up to the electronic card or the housing, the screen wall extending between the fixing tab and the second branch. the optical unit comprising a light guide illuminated by the LED, a support of the light guide holding said light guide in position, said support comprising the screen wall; the housing comprising a bottom wall arranged opposite the opening of the reflector, the electronic card being fixed to the bottom wall, the light guide having an L shape of which a first branch has one end facing the LED and a second branch which extends from the first branch at a distance from the electronic card and on the side opposite the bottom wall relative to this electronic card, the light guide support being fixed to said electronic card or to the housing; the optical unit being characterized in that the support has an L shape equivalent to the "L" shape of the light guide, comprising respectively a first branch and a second branch respectively following the first and the second branch of the light guide, means for holding the light guide, and a fixing tab extending from the second branch of the support up to the electronic card or the housing, the screen wall extending between the fixing tab and the second branch.