I am a light, set up to guide and warn the mariner from danger. I am exhibited, as a

I am a light, set up to guide and warn the mariner from danger. I am exhibited, as a beacon, upon headlands, and in places of maritime resort, from sea-marks to far-off buoy. I am exhibited, also, to show the way into harbours, and along channels, into rivers. I am a light, to point out firm land, from false lights, which are exhibited, to mislead. I am a light, to show white, green,