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.
Active recall
Section 4 of 6
Explain the main idea from light Sectors in your own words.
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 towards the white sector rather than guessing from colour alone.
Worked example · plan view
The same light can show three colours
Each boat sees the colour shining into its part of the water.
Red
Left of the plan
White
On the planned track
Green
Right of the plan
How to use the colour
- 1Find your boat relative to the light and its charted sector boundaries.
- 2Match the colour you see to the sector containing your boat.
- 3If it changes, check position, depths and your planned correction before steering.
Example only: sector bearings and the safe route come from the chart, not from a universal red-left/green-right rule.
Apply it
Use a sector as a pilotage cue
Your plan expects the light to remain white, but it changes to red earlier than the pilotage notes predict.
- 1
Recognise the cue
The colour change shows that your bearing from the light has crossed a charted sector boundary.
- 2
Control the boat
Reduce uncertainty: check heading, speed, position evidence and the planned safe sector before making a corrective alteration.
- 3
Cross-check
Compare the charted sector arcs with a second fixing method and nearby hazards; do not steer towards white by colour alone.
Sense check: A sector boundary is a line of bearing from the light, not a painted lane on the water, and its safe meaning comes from the chart.
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?
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 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
Sources and factual review
Reviewed 5 July 2026 - Day Skipper Revision.
Practice pilotage with visual aids
Sector lights make more sense when combined with leading lines, clearing bearings, buoyage, and safe-water planning.