When talking about traffic lights, "lights" is normal (though one would also refer to "a green light" or "a red light"). The slight problem I have with applying this to your sentence is that "the lights" normally refers to the signals controlling the traffic. So, you would expect to cross the road when "the lights" turn red, not green.
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Persian LearnerNothing is more dangerous than crossing a street when the light turns green.Nothing is more dangerous than crossing a street while/when the lights are green.