Front brake and brake light problem

[Krupator_imp]

Last night I was out in the countryside riding on roads without streetlamps and I noticed in my mirrors that using front brake wasn't making my brake light come on. At a stop light or stop sign I can squeeze the lever hard enough to make the light come on, but while moving that amount of brake is only used in highly spirited riding. I think I see what actuates the brake light, but I don't know how to adjust it. Does anybody encountered this before?

I would like to mention that I did a search on the forum and couldn't find anything on this issue. If this has been discussed could somebody please direct me to the thread?