1. Navigation
NAU 102
Lesson 11

2. Visibility of Lights When will I see the light?
If you don’t see it when expected, you could be in trouble!
Current range of visibility must be calculated.

3. Range of sighting a light depends on: Atmospheric conditions.
Visibility of Lights
Range of sighting a light depends on:
Intensity of the light.
Atmospheric conditions.
Height of light.
Height of observer.

4. The smaller of the two is the distance we can expect to see the light.
Visibility of Lights
To determine the range at which we’d see a light, we need to calculate:
Geographic Range
Luminous Range
The smaller of the two is the distance we can expect to see the light.

5. = distance of observer to horizon + distance of light to horizon
Visibility of Lights
Geographic Range
Maximum distance an observer could see a light if limited only by curvature of the earth.
= distance of observer to horizon +
distance of light to horizon

6. Visibility of Lights

7. Visibility of Lights

8. Visibility of Lights

9. Visibility of Lights

10. Visibility of Lights Horizon Distance
Horizon Distance (nm) = 1.17 * √height (ft) Or
Horizon Distance (nm) = 2.12 * √height (m)

11. GR = 1.17 * √height of eye + 1.17 √height of light
Visibility of Lights
Geographic Range = Horizon Distance of the observer + Horizon Distance of the light
GR = 1.17 * √height of eye √height of light

12. Visibility of Lights Example:
What is the geographic range of a light that is 70 ft tall for an observer 30 ft above sea level?
GR = 1.17 * √30 ft √70 ft
GR = 6.4 nm nm = 16.2 nm

13. Visibility of Lights

14. Geographic range = 6.4 + 9.8 = 16.2 nm
Visibility of Lights
Example:
What is the geographic range of a light that is 70 ft tall for an observer 30 ft above sea level?
Geographic range = = 16.2 nm

15. Maximum distance light will travel in current visibility conditions.
Visibility of Lights
Luminous Range
Maximum distance light will travel in current visibility conditions.
Depends on intensity of light (nominal range) and clarity of atmosphere (visibility).

16. Visibility of Lights Nominal range A measure of light intensity.
Maximum distance light will be seen if visibility is 10 nm.
Stated in Light List, List of Lights, on chart.

17. Visibility of Lights 360 Chesapeake Light 36 54 17N 75 42 46W
Fl (2) W 15s   0.1s fl 2.9 sec   0.1s fl 11.9 sec
117 19
Blue tower on white square superstructure on four black piles, CHESAPEAKE on sides.
Emergency light of lower intensity will be displayed when main light is
inoperative. RACON: N (- •). HORN: 1 blast ev 30s (3s bl).
Operates continuously.

18. Visibility of Lights Visibility
An estimate of the clarity of the atmosphere.
Particles in the air (fog, haze, smog, etc.) scatter and absorb light.
On any particular day, light from a beacon may travel more or less than the nominal range.

19. Visibility can be estimated using the International Visibility Code.
Visibility of Lights
Visibility can be estimated using the International Visibility Code.

20. Entering arguments: nominal range & visibility.
Visibility of Lights
Luminous Range is calculated using a luminous range diagram in the Light List.
Entering arguments: nominal range & visibility.

21. Visibility of Lights Example
What is the luminous range of a light whose nominal range is 19 nm when visibility is 5 ½ nm?

22. Visibility of Lights Visibility = 5 ½ nm? ANS: LR = 13 nm
Nominal range = 19 nm
Visibility = 5 ½ nm?
ANS: LR = 13 nm

23. Visibility of Lights
Range of visibility is the smaller of Geographic Range and Luminous Range.

24. Visibility of Lights Example
What will be the range of a light that is 70 ft tall with a nominal range of 19 nm for an observer whose height of eye is 30 ft when the visibility is 5 ½ nm?
GR = 16.2 nm
LR = 13 nm
Range = 13 nm

25. Introduction to Navigation
Questions?