A masthead light is a white light placed over the fore and aft centreline of a pleasure craft, shining constantly and so affixed as to show the light from straight ahead and to either side of a pleasure craft.
The arc of the lights and color allows you to determine the direction a vessel is moving. How good are your lights? You should test them to see how visible you might be at night. Whether on a trailer or at the marina, switch on your lights and see how well they can be seen. Walk away from the boat or row away, if you are at anchor or at a mooring, and see how visible the lights are as you move further away. How easy are they to see against the background of lights on shore?