Every lighthouse light has its own characteristics – 1. the number of flashes per minute, 2. it’s range, which is dependent on intensity, lenses, and height, and 3. the number of beams from the light, plus other identifying features.
Flashes per Minute
The number of flashes per minute is regulated by the speed of rotation which is governed by the motor turning gears to drive the light around. The old heavy Fresnel lens lights sat on a bath of mercury and rotated in the early days from a hand-wound clockwork mechanism, later to be replaced by an electric motor, and later to be replaced altogether.
Enclosed lights such as the DCB-10 and DCB-36 (originally used as airport beacons) were only driven by electricity and gearing regulated the speed of rotation.
Each light in a certain area has a unique characteristic.
Picture yourself coming in at night on a boat in the early days. From 10 miles out you see two lighthouses flashing. You know your approximate position but exactly where are you? With the knowledge of the characteristic of each lighthouse flash, you could identify the two lights, and also take a bearing on the lights from your position giving you an even better idea of where you were.
Intensity of the Light
The intensity of the light, and hence the distance it can be seen is regulated by the lenses through which the light must pass. Again, the old Fresnel lenses were made specifically for one location and one height, so that they gave optimum light. They worked well with liquid and gaseous fuels, but were excellent with electric lamps. Some had electric lights of one thousand (1000) watts which produced light beams that projected up to fifteen (15) miles (24 kms), depending on the height.
With the advent of plastic lenses and automation, where light wattage was reduced, the intensity of the lights was cut drastically.
Other Identifying Characteristics
There were other characteristics that marked a light as well. Some lights had twin (two) beams. These were mainly from the old Fresnel lenses which were made with two bullseyes in the center of the lens. One example of that is Pachena Point lighthouse on Vancouver Island, BC. This light was easily identifiable.
Another characteristic was a range. This was a marker light on the light tower, which looked a lot like a port or starboard navigation light, as it only shone in one direction over a range of angle. It was used to identify hazards (red light) or safe passage (green). Ranges usually marked offshore reefs or hazards, or a passage between two offshore reefs or hazards. One example of this is the light at Pulteney Point.
There are other examples of range lights, but I will not go into them here.
A couple of other characteristics of lights which were not used for navigation and were not know by the general public were the masking of the light. As the light rotates on a horizontal plane, it should be visible from all 360 degrees of the circle, but some lights were only meant to shine to seaward.
On McInnes Island, where I was stationed for twenty-five (25) years, the back sectors of the light tower glass were painted over so that the light was not visible deep inside Milbanke Sound. The official government List of Lights-Pacific Coast marked the light as a landfall light (see the Glossary), so we were required to paint out the back side of the lantern as the motor vessel Thomas Crosby V reported that the light was visible from Seaforth Channel near Ivory Island lighthouse.
Another masking of the light was done in the days before the Canadian government decided to try automating the lighthouses. Mariners and the public were not really aware of the necessity for this masking.
In the early days, pre-1970s and automation attempts, the lights were shut off one hour after sunrise and relit one hour before sunset. As the keeper had no idea in which position the lenses of the light would stop. If the light was a large Fresnel lens type and was near any type of burnable landscape, canvas curtains were drawn around the inside of the light tower to prevent the sun from shining through the lens which might have started a fire – like the focused beam from a magnifying glass.
One such type of curtain is visible on the light at Pachena Point in the photo. Not all lights needed curtains because of small size or location (middle of the sea).
So you can see, a lighthouse light has many characteristics which help the mariner. What will they do when all are automated?
The Pachena Point lighthouse photo with the curtain drawn partially around the light (landward side) is from Bob Wilson. When Bob was on Pachena Point in 2009 he wrote some very interesting letters which you can read here. He does not seem to be doing any more letter writing so I asked him if he would write for this website. He did say he was too busy, but if enough comments come in he might change his mind.