Skip to content >>

Visual Signals - Conspicuity

Conspicuity is defined as the "quality of an object or a light source to appear prominent in the surroundings", by CIE publication no. 17.4: International Lighting Vocabulary; 845-11-30.

This has traditionally been treated as a subjective concept; hence there is no readily available measure or assigned units for conspicuity.

The R&RNAV Visual Signalling section has developed a visual conspicuity model called the Marine AtoN Lights Calculator. The idea behind this application is to provide a useful tool and also a learning platform.

Conspicuity encompasses many parameters including:

  • Intensity of light
  • Colour of light
  • Atmospheric visibility/weather conditions
  • Flash character, shape and repetition rate
  • Contrast of light with background lighting (colour and intensity)
  • Size of light source
  • Shape of light source
  • Movement of light and surroundings
  • Observer's eye adaptation state (daylight or night time)
  • Distance from light to observer

This list is not exhaustive but when considering how all these parameters interact, any model will be complex.

Background Lighting Example

Factors affecting Conspicuity

  • Adaptation (eye state)
  • Knowledge/Experience
  • Colour Contrast
  • Illuminance Contrast
  • Illumination (Int/Dist2)
  • Angular subtense
  • Perceived Shape
  • Visibility
  • Distance
  • Flash Profile
  • Colour
  • Intensity
  • Size
  • Shape
  • Rhythmic Character
  • Synchronisation
  • Flooding
  • Movement
  • Background Luminance
  • Rival Lights (Intensity)
  • Colour


Synchronising several AtoN lights can increase conspicuity considerably. This technique is very effective for several buoys marking a channel, for port and starboard port entry lights or for leading lights. When viewed at a distance, the effect of several lights all coming on together over a wide area is highly conspicuous. However, if all AtoN lights in the synchronised group have the same rhythmic character, there can be problems in identifying individual AtoNs within the group. This is particularly relevant in poor visibility, when perhaps only one of the AtoNs can be seen at any one time.

It is possible to retain individual characters within a group of AtoNs and synchronise them at the start of the rhythmic character with the longest period. For this to be practicable, the AtoN characters need to have a common period or exact divisions of the longest period (or exact multiples of the shortest period).

Video: Synchronised Lights Viewing Trial