Brights are a car’s headlights when you switch them to the strongest setting — the beam that reaches far down the road. In American English, drivers say turn on your brights or dim your brights (meaning switch them back to the lower lights). You use them on dark, empty roads; you turn them down when another car is coming, so you do not blind the other driver. This is a plural-only use: we say the brights, not a bright, for this meaning. It is simply the adjective bright plus -s. In British English, people more often say full beam or main beam; brights sounds American, though British speakers will still understand it. That is not the same as the bright lights of a big city, and it is not the brights you separate in the washing machine (the colourful clothes). Here it is only the strong headlights.