Lights on vessels must be displayed at night or in restricted visibility, per COLREGs

When must lights be displayed on vessels? A simple rule that saves lives

Picture this: you’re at the helm as the sun slips below the horizon. The water takes on a glassy, dark blue, and you notice a faint shimmer ahead—the outskirts of a vessel, maybe a fishing boat or a sailboat tacking along. In moments like these, lights aren’t decorative accents; they’re life insurance. The key rule is straightforward: display lights at night or in restricted visibility.

Let me explain why that matters and what it looks like in practice.

Why lights exist in the first place

Navigation lights are like a language you speak with other mariners. They tell you:

• that a vessel is there at all,

• roughly how big it is, and

• which direction it’s heading or what action it might take next.

This isn’t a fancy suggestion, it’s a safety protocol. When visibility is limited—by darkness, fog, heavy rain, or spray—your lights become a beacon that helps others predict your path and avoid a collision. It’s the maritime equivalent of turning on headlights when fog rolls in on a country road.

Restricted visibility: what counts?

So, what exactly is “restricted visibility”? It’s not a weather forecast, it’s a practical condition that reduces how well you can see other boats, obstacles, or land features. Fog thick enough to blur silhouettes, heavy rain, snow, mist, smoke, or any combination that limits how far or how clearly you can perceive other vessels. If you’re in that situation, you must display lights as if you were navigating in the dark—even if the sun is up but the sky is dull and hazy.

This distinction is important. Daylight reduces the need for lights because natural light helps you see vessels from a distance. But when visibility dips, lights kick in as your crucial cooperative signal.

Not every bad weather moment means lights must come on

It’s tempting to think, “If it’s stormy, lights should be on.” Not quite. The safest rule is to switch to lights when visibility is restricted, not merely when the weather looks ominous. For example, you might be in bright sunlight with rain showers; if the rain reduces visibility in a way that makes other boats harder to see, you should display the proper navigation lights. If you’re in open, clear conditions with good daylight, you generally don’t need to rely on navigation lights for visibility purposes. The point is to be responsive to what you actually see and what other mariners can see.

Harbors aren’t magic shields

Some folks imagine lights are only essential in harbors or at night close to land. The truth is broader: the rule applies wherever you’re underway and visibility is restricted. On the open sea or a river, a vessel could be approaching from far away in fog. In that moment, your lights help others interpret your size, speed, and intended maneuvers. The coast guard knows this, and so do skippers who respect the COLREGs. The goal isn’t to police the harbor alone; it’s to keep the whole waterway safer, 24/7, in all kinds of conditions.

What lights actually look like on vessels

If you’ve ever wondered what “displaying lights” means in practice, here’s a crisp snapshot:

• Sidelights: A red light on the port (left) side and a green light on the starboard (right) side. These tell others which way you’re oriented.

• Masthead light: A white light positioned high forward, visible from ahead and to the sides. It signals that the vessel is underway.

• Stern light: A white light placed toward the stern (rear) of the vessel, visible behind you.

• Anchor light: A white all-around light that means “I’m anchored.” You’ll see this when a vessel is stationary in open water or in a crowded harbor.

There are also other lights for specific situations (like when a vessel is not under way or when it’s a tug, a fishing vessel, or a sailing vessel), but the core idea remains simple: lights should show your presence, position, and potential motion, especially when others might not see you clearly.

How this plays out on the water: quick scenarios

• A small fishing boat in fog: The fog muffles sounds and eyes better not rely on the senses alone. The fishing boat should show its navigation lights so approaching vessels can gauge distance and direction, reducing the risk of a close-quarters situation.

• A sailboat at dusk: Even as daylight lingers, the moment light fades, a sailboat should have its lights on if it’s under way. The white masthead light and side lights let others know you’re moving and roughly where you’re headed.

• A powerboat leaving a marina in a light drizzle: You might still be within the visible range of nearby craft, but restricted visibility due to drizzle means you should switch on the appropriate lights to communicate your presence and your intended action.

• A vessel anchored in a busy channel at night: An anchor light helps approaching traffic distinguish a stationary target from a moving one, a crucial difference in a choke point or narrow passage.

A few practical tips to stay shipshape

• Check your lights before you head out. A quick routine—switch, look, adjust—can save you from a blinding mistake or a near-miss.

• Keep lenses clean. A dirty lens dims the signal you’re trying to send, which defeats the purpose of the light.

• Carry spares. Bulbs burn out, wiring wears, fuses pop. Having replacements on board isn’t overkill; it’s common sense.

• Test electrical circuits. If a light doesn’t come on when it should, troubleshoot promptly. A faulty light is a blind spot for others.

• Know your vessel’s lighting requirements. Different boats and different activities call for different light configurations. It’s not just about turning something on; it’s about the right light at the right height and in the right color.

A quick, practical takeaway

The core idea is simple and elegantly practical: you must display lights at night and any time visibility is restricted. Daytime conditions without heavy haze or fog generally don’t demand lights for visibility, but if conditions change and visibility drops, lights come on. It’s all about making your location obvious to others and guiding their expectations about what you might do next.

A few thoughtful musings

If you’ve ever driven a car with headlights in fog, you know the difference they make. The same logic applies on the water—except with more moving parts, more variables, and a life vest in the mix. The rules of the road are human-friendly at heart: they translate to a universal signal language. When you show your lights, you’re not just following a rule—you’re signaling a shared intent to navigate safely together.

Embracing the rhythm of the sea

One of the overlooked beauties of the COLREGs is how they blend precision with practicality. The requirement to display lights at night or in restricted visibility isn’t about rigidity; it’s about a dimension of timing that respects the ebb and flow of weather, traffic, and human judgment. You get a sense for the rhythm of the water—the way sounds travel differently over dusk-tinted waves, how a distant glow hints at a vessel’s approach, how a small sail silhouette can suggest a larger story about its course.

If you’re new to this, start with the big picture: lights signal presence and intention in conditions where sight is compromised. Then layer in the details—positions, colors, and the concept of “underway” versus “anchored.” You’ll find the pieces click into place, and the rule becomes less about memorization and more about naturally staying predictable and safe on the water.

A final thought

Safety on the water isn’t about checking boxes; it’s about a mindset. The lights you display aren’t just legal requirements; they’re signals of consideration for every other mariner you share the water with. When you’re out there, night or in restricted visibility, think of your lights as a lighthouse you carry with you—a quiet, steady reminder that visibility is a shared responsibility.

If you’re curious to deepen your understanding, keep an eye on the common-sense details that often show up in real-life stories: positioning, timing, and the subtle cues other vessels use to interpret your moves. Those cues are the practical heartbeat of COLREGs in action. And with lights dawned or dusk-shaded, you’ll be navigating with clarity, confidence, and a touch more grace on every voyage.