Same for you. Need a little more detail to get a point for the one
question listed below.

Nav wrote

DSK wrote:

Bart Senior wrote:


1 pt each
What are the factors that determine a single light's visible range?

The height and the brightness


To be more precise, the height determines the geographic range while
visible range is limited by conditions as well as luminosity and colour.


Cheers (call me Nav)

It is remarkable that you prefer a long winded yet incomplete answer to
that which gives _all_ the factors without being longwinded. Was may
answer not precise enough?

:P

Cheers


Bart Senior wrote:

Same for you. Need a little more detail to get a point for the one
question listed below.

Nav wrote

DSK wrote:


Bart Senior wrote:



1 pt each
What are the factors that determine a single light's visible range?

The height and the brightness


To be more precise, the height determines the geographic range while
visible range is limited by conditions as well as luminosity and colour.


Cheers (call me Nav)

You didn't account at all for the curvature of the earth.

Yes, I do prefer more complete answers. The idea here
is to pass on information to other readers. Details count.

Nav wrote
It is remarkable that you prefer a long winded yet incomplete answer to
that which gives _all_ the factors without being longwinded. Was may
answer not precise enough?

Bart Senior wrote:
Same for you. Need a little more detail to get a point for the one
question listed below.

DSK wrote:
Bart Senior wrote:

1 pt each
What are the factors that determine a single light's visible range?

The height and the brightness

To be more precise, the height determines the geographic range while
visible range is limited by conditions as well as luminosity and colour.

Cheers (call me Nav)

Good descriptive answers Doug, but not quick enough for points.

Not enough information for the one below. No points awarded for it yet.
Care to expand on it?

DSK wrote in message
...
Bart Senior wrote:

1 pt each
What are the factors that determine a single light's visible range?

The height and the brightness

Bart Senior wrote:

Good descriptive answers Doug, but not quick enough for points.

Not enough information for the one below. No points awarded for it yet.
Care to expand on it?

Well, you can get quite dogmatic about determining a light's visible range.
The two keys are height & brightness.

Because the earth (and thus the surface of the sea) is spherical, the
higher the light is, and the higher the observer's eye, the further away it
will come over the horizon. There is a formula for determining this, adding
the two heights and multplying by a factor to get whatever distance units
you like. This is called the geographic range.

Brightness is also specified for major & minor lights, this is the reason
for the elaborate Fresnel lenses on lighthouses... to increase the
effective brightness. Obviously a tiny bulb connected to a AAA battery is
not going to be seen as far away as large halon floodlight connected to
high amp 120VAC. This is termed luminous range, and is usually the limiting
factor. It is affected very much by atmospheric conditions. In most nav
references there are tables for determining the luminous range of a given
light in given conditions.

The visible range of a light is the lesser of the geographic range and the
luminous range under prevailing atmospheric conditions.

If one is navigating towards a landfall, and expecting to see a light
during the approach, it is good practice to work out the visible range of
the light under current conditions, plot it against one's future DR, and
tell the watch on deck when to expect to see it. If a long time goes by and
no light, then it's time to work on an alternate approach... and a good
excuse...

Fresh Breezes- Doug King

2 points to you Doug--an extra point for the lengthy detailed
description.


DSK wrote
Bart Senior wrote:

Good descriptive answers Doug, but not quick enough for points.

Not enough information for the one below. No points awarded for it yet.
Care to expand on it?

Well, you can get quite dogmatic about determining a light's visible
range.
The two keys are height & brightness.

Because the earth (and thus the surface of the sea) is spherical, the
higher the light is, and the higher the observer's eye, the further away
it
will come over the horizon. There is a formula for determining this,
adding
the two heights and multplying by a factor to get whatever distance units
you like. This is called the geographic range.

I'm not entirely sure I understand your method. But you hit thed key
points,
height of eye for the observer, and height of the light are both limited by
the curvature of the earth and the horizon--even if the light is luminous
enough to be seen at greater distances.

I typically calculate the horizon for my height of eye, and also for the
light
based on it's height and add the two together, and check this against the
specs on the light, which is usually greater. The horizon is usually the
limiting
factor for major lights that are visible at greater ranges.

Brightness is also specified for major & minor lights, this is the reason
for the elaborate Fresnel lenses on lighthouses... to increase the
effective brightness. Obviously a tiny bulb connected to a AAA battery is
not going to be seen as far away as large halon floodlight connected to
high amp 120VAC. This is termed luminous range, and is usually the
limiting
factor. It is affected very much by atmospheric conditions. In most nav
references there are tables for determining the luminous range of a given
light in given conditions.


Fresnel lenses are amazing techonology. Have you seen one up close?

The visible range of a light is the lesser of the geographic range and the
luminous range under prevailing atmospheric conditions.

If one is navigating towards a landfall, and expecting to see a light
during the approach, it is good practice to work out the visible range of
the light under current conditions, plot it against one's future DR, and
tell the watch on deck when to expect to see it. If a long time goes by
and
no light, then it's time to work on an alternate approach... and a good
excuse...

Fresh Breezes- Doug King

Bart Senior wrote:

2 points to you Doug

Yeehaw, does this mean I'm winning?!?



I'm not entirely sure I understand your method. But you hit thed key
points,
height of eye for the observer, and height of the light are both limited by
the curvature of the earth and the horizon--even if the light is luminous
enough to be seen at greater distances.

Right... in which case, you might see the "loom" of the light's glow over the
horizon. Very reassuring to see this!



I typically calculate the horizon for my height of eye, and also for the
light
based on it's height and add the two together, and check this against the
specs on the light, which is usually greater.

IIRC you should add the heights first, then calculate the horizon. There is an
exponent in the formula which will throw you off. I'm usually in a hurry and
just interpolate from the tables in the appendix....


Fresnel lenses are amazing techonology. Have you seen one up close?

Yes, been inside one of the big ones. They are amazing.

One of the mysteries of history is what happened to the Cape Hattaras lighthouse
Fresnel lens at the outset of the War of Northern Aggression... some
Confederates thought it would be a good idea to swipe it, since it was very
expensive and, in place, could only benefit the Union Navy. Sketchy research
indicates that they hid it somewhere far inland, possibly on a farm in Vance
County (which means it's most likely under Kerr Lake now). There are still only
a few 1st-order Fresnel lenses on US lighthouses, IIRC the Cape Hatteras light
was only given a 2nd-order after the war.

Fresh Breezes- Doug King

You forgot COLOR!!!!

Cheers

Bart Senior wrote:
2 points to you Doug--an extra point for the lengthy detailed
description.


DSK wrote

Bart Senior wrote:


Good descriptive answers Doug, but not quick enough for points.

Not enough information for the one below. No points awarded for it yet.
Care to expand on it?

Well, you can get quite dogmatic about determining a light's visible

range.

The two keys are height & brightness.

Because the earth (and thus the surface of the sea) is spherical, the
higher the light is, and the higher the observer's eye, the further away

it

will come over the horizon. There is a formula for determining this,

adding

the two heights and multplying by a factor to get whatever distance units
you like. This is called the geographic range.


I'm not entirely sure I understand your method. But you hit thed key
points,
height of eye for the observer, and height of the light are both limited by
the curvature of the earth and the horizon--even if the light is luminous
enough to be seen at greater distances.

I typically calculate the horizon for my height of eye, and also for the
light
based on it's height and add the two together, and check this against the
specs on the light, which is usually greater. The horizon is usually the
limiting
factor for major lights that are visible at greater ranges.


Brightness is also specified for major & minor lights, this is the reason
for the elaborate Fresnel lenses on lighthouses... to increase the
effective brightness. Obviously a tiny bulb connected to a AAA battery is
not going to be seen as far away as large halon floodlight connected to
high amp 120VAC. This is termed luminous range, and is usually the

limiting

factor. It is affected very much by atmospheric conditions. In most nav
references there are tables for determining the luminous range of a given
light in given conditions.



Fresnel lenses are amazing techonology. Have you seen one up close?


The visible range of a light is the lesser of the geographic range and the
luminous range under prevailing atmospheric conditions.

If one is navigating towards a landfall, and expecting to see a light
during the approach, it is good practice to work out the visible range of
the light under current conditions, plot it against one's future DR, and
tell the watch on deck when to expect to see it. If a long time goes by

and

no light, then it's time to work on an alternate approach... and a good
excuse...

Fresh Breezes- Doug King