How do you tell cardinal marks apart at night?

By the number of quick white flashes, arranged like the hours on a clock face. East gives three flashes (3 o’clock), south six plus a long flash (6 o’clock), west nine (9 o’clock), and north flashes continuously. The long flash after the six is there so you do not mistake a six for a three or a nine.

What is the difference between a Q and a VQ light?

The frequency. Q (quick) is 50 or 60 flashes per minute, VQ (very quick) is 100 or 120. Cardinal marks use either, depending on the buoy, but always with the same flash count for a given direction.

Which marks show a white light?

Cardinal marks, the isolated danger mark and the safe water mark. Each has a different rhythm so they cannot be confused: cardinals flash fast (VQ or Q), isolated danger is Fl(2), and safe water shines calmly (isophase, occulting, a long flash every 10 s, or Morse „A”).

Light characteristics

At night you recognise a mark not by its paint but by the rhythm and colour of its light. On the chart and in the list of lights the rhythm is written in abbreviations. Here is what the important ones mean, and what they look like in the IALA system.

The abbreviations to know

Code	Name	What it means
F	fixed	Shines continuously, no breaks.
Fl	flashing	A short flash, a longer pause. Less light than darkness.
Fl(2)	group flashing	A group of flashes (here two), then a pause. Fl(2) is the isolated danger mark.
Fl(2+1)	composite group flashing	A group of two flashes, then one more. The preferred channel mark rhythm.
LFl	long flash	A single flash lasting at least 2 seconds.
Q	quick	50 or 60 flashes per minute, continuous or in groups.
VQ	very quick	100 or 120 flashes per minute. The cardinal mark rhythm.
Iso	isophase	Light and darkness of equal length.
Oc	occulting	More light than darkness: short eclipses.
Al	alternating	Changes colour, like the blue and yellow of the wreck buoy.
Mo(A)	Morse code	The light transmits a Morse character, here the letter „A”: a short flash and a long flash. One of the safe water mark options, alongside Iso, Oc and LFl.10s.
every 10s	period	The full light cycle takes that many seconds. For example „Fl(3) 10s”.

Cardinal marks: flashes like a clock face

The four cardinal marks all show a white light; what separates them is the number of quick flashes, arranged like hours on a clock: east is three flashes, south six, west nine. North flashes without a pause. After the six comes a long flash, so you do not confuse it with a three or a nine. Watch the difference below.

North cardinal mark (N) VQ or Q

East cardinal mark (E) VQ(3) every 5 s or Q(3) every 10 s

South cardinal mark (S) VQ(6)+LFl every 10 s or Q(6)+LFl every 15 s

West cardinal mark (W) VQ(9) every 10 s or Q(9) every 15 s

The rhythm in the animation is illustrative (shortened so a cycle is watchable). The binding record is the one in the list of lights and on the chart.

Frequently asked questions

How do you tell cardinal marks apart at night?: By the number of quick white flashes, arranged like the hours on a clock face. East gives three flashes (3 o’clock), south six plus a long flash (6 o’clock), west nine (9 o’clock), and north flashes continuously. The long flash after the six is there so you do not mistake a six for a three or a nine.
What is the difference between a Q and a VQ light?: The frequency. Q (quick) is 50 or 60 flashes per minute, VQ (very quick) is 100 or 120. Cardinal marks use either, depending on the buoy, but always with the same flash count for a given direction.
Which marks show a white light?: Cardinal marks, the isolated danger mark and the safe water mark. Each has a different rhythm so they cannot be confused: cardinals flash fast (VQ or Q), isolated danger is Fl(2), and safe water shines calmly (isophase, occulting, a long flash every 10 s, or Morse „A”).