errr your concept of light is wrong so i am only going to comment on that. Won't getting into argument of flat earth as @Xulfiqar already proved that.
Please light up entire hall with just single LED bulb. Clearly it is you who is on local kuppi and sasti charas.
Seeing a light/light source is different than getting a light to shine something. I will give a simple example, headlight can shine the road up to 1km (lets say). If same bulb is removed from headlight, it won't shine anything above 3 meters. BUT you can still see the bulb well away from 1km. Lighthouse is not supposed to brighten up whole ocean, boats are supposed to see the light source and they do.
I have got a very powerful LED flashlight and most it can throw its light when humidity and dust are least is 1 kilometer. Why can't it travel 1000 kilometers genius since you want lights of lighthouses on flat earth to be seen thousands of kilometers away?
Because when you shine your LED flashlight, as it travels farther, slightest angle at source makes large angle when distance is increased. Light is not losing its intensity, it is simply getting scattered. If you can really focus all the light into one direction then what you get is called LASER.
If light loses its intensity, we do we see stars that are millions miles away? I am sure atmosphere of earth is not clear.
So please clear your concepts, getting light to shine something up is different than seeing a light source itself. Have you ever been to plane? I can see lights of cities from 39000 feet above ground. Those lights cannot shine the plane but i can see em. I will share some pictures later for you
EDIT: have a look here at laser rangefinder https://en.wikipedia.org/wiki/Laser_rangefinder
It can measure up to 20km distance which means that light is traveling a total of 40km without losing intensity. Its not some special 10000watt bulb that has a lot of intensity, its all magic of lenses to focus and guide the light in one direction
