Originally Posted by
AntsUiga
Does anyone have any background to explain the brightness?
As an entertainment lighting designer I have some overlaping background. I don't know much about lighthouses though.
A French physicist Augustin-Jean Fresnel invented the lens for light houses.
Theater took the Fresnel lenses from the lighthouses and adapted them to stage lights. Most stage and studio Fresnel lights have a rack that moves the source and reflector towards or away from the lens thereby affecting beam spread angle. We begin to focus a light by pulling the rack back for a narrow beam, and then aim that to the center of the subject. Then we move the rack towards the lens to widen the beam and fill in the surrounding space as needed.
With lighthouses, the lens and reflector revolve around the source, or the reflector and source revolve inside the lens; the distance between source and lens doesn't change.
All elements will effect brightness, where and how the glass is made, the quality of the reflector, the source of the light, cleanliness of lens and reflector, and height above sea level.
The Sea is my Church; the Boat is my Pew.