Sector Lights in Navigation: Red, White and Green Explained

What is a sector light?

A sector light is arranged to show different colours over different bearings. As the vessel's bearing from the light changes, the observed colour can change, giving an immediate indication that the vessel has entered another charted sector.

The chart or official light publication gives the sector limits and light character. Those published details are the authority; a remembered colour rule is not.

Does a white sector always mean safe water?

Many approaches use a white sector to mark an intended line or channel, with red or green sectors indicating adjacent danger. This is common, but it is not universal and does not make every point inside the white sector safe.

Hazards, depth limits, traffic, local directions and the vessel's own draught still matter. Read the chart, sailing directions and harbour information before relying on a colour change.

How should red and green sectors be interpreted?

Red and green sectors often show which side of an intended approach the vessel has reached. Their exact meaning depends on the charted arrangement, not on the lateral-buoy convention alone.

If the colour differs from the pilotage plan, treat it as a position warning. Slow down if safe, confirm the light's identity and re-establish position using bearings, depth, buoyage, radar or another suitable independent cue.

How do sector lights fit into pilotage?

Write the expected colour and the bearings at which it should change into the pilotage plan. Add clearing bearings, transits, depths, buoyage and an abort point so that no single observation carries the whole plan.

At night, identify the light by position, colour, rhythm and period. Shore lighting, reflections, haze and nearby aids can make colour alone misleading. A sector light is powerful evidence when it agrees with the rest of the navigation picture.