Help with lights

i’ve a problem with a spot light. I did a cube with dimension 2 centered in (0,0,0). Then i put a spotlight in (5,0,0). The problem is the cube back face (in x negative) is also illuminated as it was the front face (in x positive). Why? I made a picture and put in
Thanks in advance

ops, that happened when using ambient light. Now i’m using only diffuse light and the illumination works properly.