got pull over!!!!

So, I was on my way home yesterday when I stopped at the red light, all of a sudden a cop parked drive behind me at the red light and the next thing I know was he told me to pull over. I asked him what was the reason he pulled me over for and he told me it was because I have white bulbs for my brake light. I was kinda shock because I been driving with white bulbs like forever and I never got pull over before but why now. Anyways, he gives me a citation for it.