Let me start out with the basic equipment of a sailing boat or sailing ship: two sidelights and a sternlight. All powered ships and power boats of reasonable size also need these lights. Together these three lights cover the whole 360 degrees, with one only being visible at any relative bearing except near the transitions (when two may be visible.)†
Firstly, these three lights should be mounted on the hull where they cannot be obscured by sails or boat bits, or in a combined 3-way lantern at the masthead where they also cannot be obscured by sails. Common mistake: Putting lights on the mast spreaders is almost always inappropriate (just think about spinnakers or even the mainsail blocking off the light; never mind the other considerations).
Secondly each light should be associated with a 3D screen that prevents it being seen outside its required arc. Both it and the light may be placed in the lights.x file. This is easy to accomplish, really.† A set of standard screens and standard lights meet the requirement quite easily and are widely applicable (even large ships need only increase the size of the light/screen combination). The layout of a sidelight on a real boat is shown in the diagram alongside.
The designs presented on the Technical Sheet relax the COLREGS requirements to meet the constraints of VS light implementation without incurring excessive size. The proportions of the screen design cut off lights about 22.5 degrees (1 point) beyond the required arc. Similarly, a masthead combination light would also meet the requirement for boats that can choose this option.
Most VS power boats will carry the three lights mentioned above and a mastlight also properly screened to show over the required arc. There is no more difficulty in designing such a light than any of the other three. However, remember to check that no boat parts obscure the sidelights over the required arcs. Sidelights on a short yard on a short stubby mast are possible, but would never be used on a vessel of any size. They would be too difficult to maintain and align. Sidelights are usually mounted towards the outside of the hull or on a large ship on the sides of the bridge. An overtaking light is usually mounted right on the stern or transom, or sometimes in a large ship on the end of an aft superstructure.
Some VS power boats may opt for the sidelights and one all-round white light up the mast, which is slightly simpler. The sidelights must be no higher than 75% of the height of the white light.
If you are designing a very large ship (say QEII or a tanker) or an unusual vessel such as a hovercraft, a submarine or an aircraft carrier, nothing beats reading the actual regulations unless it is looking at the real ship or detailed photographs of it. The number of masts, off-center masts, funnels, conning towers and other curiosities may affect the placement of lights.
Common mistake: some VS boats have a white light stuck on the tip of the bow. This is so wrong it is hard to know what to make of it.
Tiny boats that should not be out at sea at night do not need to carry permanent lights and such VS boats can omit them. Easy. Examples are prams, rowing shells, canoes, rafts, kayaks, inflatable boats, windsurfers, racing dinghies such as the Finn, and jetskis. However if it makes sense, boat designers wonít be too far wrong to include a single all-round white light. It would be absurd to put lights on a racing dinghy or a windsurfer (sailboard), for example.
Note that the lights should be reasonably realistic colours. You will be near enough right if you choose plain red (RGB=255,0,0) and plain green (RGB=0,255,0) for the sidelights. White is easy, just full-on RGB=255,255,255.
IMPORTANT DATA: VS lights work by simply not dimming the objects in the lights.x file as it gets dark (whereas boats, land and sea get darker), so that they show up by contrast. This means that the size of lights must be adequate to the size of ship: an ocean liner needs bigger blobs of color than a runabout in order to show up on scale. This is one of the implications of looking at boats on a screen instead of in reality. Contrast range is limited, and intense illumination (which is what real ships would do) is simply not possible.
Strict compliance with the arc regulations is difficult given the necessary size of the light blobs, but it doesnít matter too much as long as you attempt to get it right. The technical suggestions given are pretty crude but at least donít show lights more than 1 point (22.5 degrees = 1/16 of a full circle) away from where they should be seen. Closer approximations can be achieved in large VS ships with a little design work.
What is impossible to do with current VS is to change the lights according to the vesselís status. Lights are fixed objects in the current version (v3.5). Thus a sailing boat still carries underway sailing lights if it has the engine on, during the day, or even if it is at anchor! It is possible that the definition of a boat could be changed to allow for three sets of light files, displayed depending on boat status in the simulator (daytime - no lights, sailing, powered, anchored).