So the same clock have now bought but in business. It is great if you know what it may be that you sometimes glows in the dark and then again not. I have found the error very quickly. The wallpaper is almost white, thus reflecting the light from the clock to the sensor. And the clock will no longer be lit up. Then I have a piece of scotch tape taken on the adhesive side made a big black spot and glued over the Senor. Lo and behold, now she goes on when it is dark and off when light shines. Just great'm more than thrilled.