The light is red is the most common way in American English. We would not say the traffic light, if we're driving and see the light!
I don't think it is just americans that drop the traffic here - I'm English and certainly do it too. I don't believe this is a regional thing either, illexsquid. I learned this word on a bus in Bucarest - having mounted the bus and not knowing how to pay i thought to ask the driver but saw a sign in the glass between his cab and the passengers saying (in romanian) not to talk to the driver, not even 'la semaforul' As my Romanian was basic I first believed it meant not even using hand signals! I looked it up and found it meant traffic lights! It was a hilarious day in retrospect but being unintentional stowaways with my 78 year old disabled mother was not the best moment of the day - unable to pay we got off as soon as we could see a taxi! We later discovered the fine for failing to pay is less than the taxi fare from airport to city centre...
Interesting. "Semaphore" is a computer science term for a sort of signal in implementing locks. Oh, i just looked it up; it's also the word for signal flags on ships. That makes sense.