Lights to be carried by vessels under the Conservancy bye-laws. - Every steam-vessel navigating the River Thames (except as hereinafter provided) shall, between sunset and sunrise, while under way, exhibit the three following lights of sufficient power to be distinctly visible with a clear atmosphere on a dark night at a distance of at least one mile, namely: (a) At the foremast, or, if there he no foremast, at the funnel, a bright while light suspended at the height of not less than ten feet from the deck, and so fixed as to throw the light from right ahead to two points abaft the beam on either side. (b) On the starboard side, a green light so fixed and fitted with an inboard screen as to throw the light from direct ahead to two points abaft the beam on the starboard side. (c) On the port side, a red light so fixed and fitted with an inboard screen as to throw the light from direct ahead to two points abaft the beam on the port side. (d) Provided, however, that no passenger steam vessel whilst navigating the said river above London Bridge, and when under way, shall be bound to exhibit between sunset and sunrise any other lights than two bright white lights, one at her mast-head, and one at her stem. Steamers towing vessels shall, between sunset and sunrise, exhibit, in addition to the above-mentioned three lights, a white light on the foremast or funnel not less than four feet vertically above the first-mentioned white light, of the like power and similar to it in every respect. Every steam dredger moored in the River Thames shall, between sunset and sunrise, exhibit three bright lights from globular lanterns of not less than eight inches in diameter, the said three lights to be placed in a triangular form, and to be of sufficient power to be distinctly visible with a clear atmosphere on a dark night at a distance of at least one mile, and to be placed not less than six feet apart on the highest part of the framework athwart ships. All barges on the River Thames above Putney Bridge, whether navigated by sail towed by steam or horses, shall, between sunset and sunrise, while under way, exhibit in their bows or on their masts a red light of sufficient power to be distinctly visible with a clear atmosphere on a dark night at a distance of at least one mile. (The report of the committee appointed by the Board of Trade to enquire into the navigation of the Thames, which was presented to both Houses in the summer of 1879, recommended the abolition of this clause, which the committee stated "appears never to have been obeyed." ) All vessels under sail east of London Bridge shall exhibit between sunset and sunrise two lights, viz., a green light on the starboard and a red light on the port side, such lights to be visible on a dark night with a clear atmosphere a distance of at least one mile. Every person in charge of a dumb-barge when under weigh and not in tow shall, between sunset and sunrise, when below or to the eastward of a line drawn from the upper part of Silvertown, in the county of Essex, to Charlton Pier, in the county of Kent, have a white light always ready, and exhibit the same on the approach of any vessel. The person in charge of the sternmost or last of a line of barges, when being towed, shall exhibit, between sunset and sunrise, a white light from the stern of his barge. All vessels and barges when at anchor in the fairway of the river, shall exhibit the usual riding light. All vessels when employed to mark the position of wrecks or other obstructions, shall exhibit two bright lights placed horizontally not less than six feet apart.
    The penalty for breach of any of these bye-laws is a sum not exceeding £5.- (And see RULE OF THE ROAD.)

Charles Dickens (Jr.), Dickens's Dictionary of the Thames, 1881