Lights
What Is a Sectored Light? How to Use Sector Lights
Published · Last checked October 2026
A sectored light shows different colours, or is visible or hidden, depending on the bearing you view it from. Typically a white sector marks the safe approach, with red and green sectors either side warning that you have strayed off the line. Sectors are given on the chart and in the light list as true bearings from seaward towards the light. Watching the colour change tells you which side of safe water you are on, even when you cannot see anything else.
How sector lights work
The lighthouse or beacon has coloured screens in front of the lamp, so it shows one colour over one arc and another colour over a neighbouring arc. On the chart you will see the sectors drawn as coloured arcs around the light, with the boundaries marked. The light's description lists the colours, for example 'Oc WRG 10s', meaning occulting white, red and green every 10 seconds, showing different colours on different bearings.
Common types
- Directional light (Dir): a narrow white sector along a channel, with red and green sectors either side. Often very precise.
- Danger sectors: a red sector covering an area with rocks or shoals; stay in the white.
- Obscured sectors: where the light is hidden by land or deliberately blanked off.
- Intensified sector (Intens): brighter over a particular arc, usually to reach further along an approach.
Reading sector bearings
Sector limits are always given as true bearings from seaward towards the light, read clockwise. That catches people out: if the chart says white from 040° to 050°, you are in the white sector when the light bears between 040° and 050° from you.
| Bearing of light from you | Colour seen | Meaning |
|---|---|---|
| 041° to 044° | Green | You are off the line; move back towards the white |
| 044° to 046° | White | On the safe approach |
| 046° to 049° | Red | You are off the line on the other side |
Which side the red and green fall varies with the light, so always check the chart. Many follow the local lateral convention, with red on the port side and green on the starboard side for a vessel heading in, but not all do.
Using them in practice
- Plan the approach in daylight: note the sector bearings and colours in your pilotage plan.
- Get into the white sector well before the narrow part of the approach.
- Steer to keep in the white, checking your compass heading against the expected bearing.
- Correct gently if the colour changes, allowing for tidal stream.
Sector lights pair well with a leading line by day. Learn more in the night sailing lesson and the light characteristics guide.
Range and visibility
Coloured sectors are usually visible over a shorter range than white. The light list gives a separate nominal range for each colour, for example 'W15M R11M G11M', so you may see the white sector well before the red or green. Also remember that the light can be obscured by land or haze near the edges of the coast. In good visibility, a lighthouse may appear above the horizon as a loom of light before the lamp itself is visible, so do not mistake the loom for the sector you are in until you can see the light clearly.