Lights. - Circles drawn on charts round a light are not intended to give information as to the distance at which it can be seen, but solely
indicate, in the case of lights which do not show the same characteristics or colours in all directions, the bearings between which
the differences occur.
All the distances given in the Light Lists and on the charts for the visibility of lights are calculated for a height of an observers eye of
15 feet. The table of distances visible due to height, at the end of each Light List afford a means of ascertaining how much more or less the
light is visible should the height of the bridge be more or less. The glare of a powerful light is often seen far beyond the limit of
visibility of the actual rays of the light, but this must not be confused with the true range. Again, refraction may often cause a loight
to be seen further than under ordinary circumstances.
When looking out for a light at night, the fact is often forgotten that from aloft the range of vision is much increased. By noting a star
immediately over the light a very correct bearing mat be afterwards obtained from the standard compass.
The intrinsic power of a light should always be considered when expecting to make it in thick weather. A weak light is easily obscured
by haze, and no dependence can be placed on its being seen.
The power of a light can be estimated by remarking its order, or candle power, as given in the Light Lists, and in some cases by noting
how much its visibility in clear weather falls short of the range due to the height at which it is placed. Thus, a light standing 200 feet above
the sea, and only recorded as visible at 10 miles in clear weather, is manifestly of little brilliance, as its height would permit it to be
seen over 20 miles, if of any power.
The distance from a light cannot be estimated either by its brilliancy or its dimness.
On first making a light from the bridge, by at once lowering the eye several feet and noting whether the light is made to dip, it may be
determined whether the vessel is in the circle of visibility corresponding with the usual height of the eye or unexpectedly nearer the light.