Module 12 - Visual Aids to Navigation
Sector Lights in Navigation: Red, White and Green Explained
Quick answer
A sector light shows red, white, or green over different bearings. The colour you see tells you whether you are in the planned sector, near a channel edge, or standing into danger.
- White often marks the preferred safe-water sector.
- Red or green sectors usually warn that you have moved out of the intended line.
- Always check the chart: sector colours are guidance, not a replacement for pilotage planning.
Many navigation lights show different colours in different directions, called sectors. Sector lights help vessels follow a safe approach line or keep clear of dangers. A white sector often marks the preferred or safe water, while red and green sectors warn that you are outside the safe track or approaching a danger.
Sector boundaries are shown on the chart as dashed lines radiating from the light. The colours are given as abbreviations: W (white), R (red), G (green). When the light changes colour, you have crossed a sector boundary and should check your position immediately.
In pilotage, sector lights are useful because they provide continuous feedback. If the planned approach keeps you in the white sector, seeing red or green tells you that tide, leeway, or steering error has pushed you off track.
Worked pilotage example: your harbour plan keeps the yacht in the white sector on the leading approach. If the light changes from white to red, hold your nerve, check the charted sector boundaries, then make the planned correction back toward the white sector rather than guessing from colour alone.
A colour change is useful feedback: it tells you that your bearing from the light has moved into a different sector.
Key points
- White sector often = safe channel
- Red/Green sectors often = warning of danger or channel limits
- Sector boundaries shown as dashed lines on chart
- Colour change = you have crossed a sector boundary
- White is often preferred water, but the chart remains the authority
Common mistakes
- Treating all white sectors as automatically safe without checking the chart.
- Forgetting that the colour depends on where your boat is relative to the light.
Quick practice check
Try a few questions before you move into the full module.
1. What is the main purpose of a sector light?
2. On an approach planned through the white sector, what does a change from white to red normally mean?
3. Why should you not assume every white sector is automatically safe?
Common questions
What is a sector light in navigation?
A sector light is a navigation light that shows different colours in different directions. The colour you see helps identify safe water, channel limits, or nearby danger.
What does it mean when a sector light changes from white to red?
It means you have crossed a sector boundary. Red often warns that you are leaving the safe sector or approaching a danger.
Keep revising this topic
Last reviewed: 5 July 2026 by Day Skipper Revision
Practise pilotage with visual aids
Sector lights make more sense when combined with leading lines, clearing bearings, buoyage, and safe-water planning.