Sector Lights in Navigation: Red, White and Green Explained
How sector lights work in pilotage, what red, white and green sectors mean, and how Day Skipper students should use light sectors with charts and bearings.
A sector light shows different colours in different bearings
A sector light is built so that it shows different colours from different directions. As your bearing from the light changes, the colour you see can change from white to red or green.
On the chart, each sector is shown with bearings and colour labels. Those charted sectors are the authority; never assume the white sector is safe without checking the charted limits and local notes.
White is often the intended channel, but context matters
Many sector lights use a white sector to mark an intended approach or channel, with red or green sectors warning that you are standing into danger or outside the preferred line.
The exact meaning depends on the harbour or approach. Some sectors mark danger, some mark alignment, and some help separate a safe lead from adjacent hazards. Read the chart and almanac before relying on the colour change.
Use sector lights with bearings and a pilotage plan
A sector light is most useful when it is part of a pilotage plan: expected colour, clearing bearings, transits, depths, buoyage and a decision point if the colour is not what you expected.
At night, identify the light by position, colour, rhythm and period. Do not rely on colour alone if there are other lights, shore lighting, reflections or poor visibility.