I'll give you an example with a very tight beam - a laser.
Suppose you have a very bright laser with a beam diameter of 3mm. You measure the radiated power at 1m and find it is 1W. Now you shine that laser at a target 8Km away (5 miles) and the spot on the target is 3m across. Not the tightest laser beam, but OK.
The beam now covers a surface area 1,000,000 times larger than it did at 1m. Area = πr2 The total energy is the same (minus air absorption) just spread out over a much larger area. If you took your power meter with a 3mm aperture (same as the beam's original diameter) you'd measure 1 microwatt of power. Got it? The beam now covers 1 million times more surface area so at any given point it is 1 million time less powerful.
Now that we know that - calculate the light power at your target using the inverse square law from 1m to 8000m. Tell me if they are close to the same.
Now I am starting to worry. Maybe you are not trolling, Maybe you are positively, honestly unaware of the difference between
conservation of energy and
inverse square law!
What you are saying, that the same watt of power is there when you look at it 8 km away, is the principle of
conservation of energy! What you are saying that does not apply to spotlights is the
inverse square law! The inverse square law is exactly what you described in your explanation. At a certain distance the energy density will be a million times lower and the area covered will be a million times larger than close to the source.
If you want to apply your inverse square law again, at 16 km the energy density will be a quarter of the energy density at 8 km, and the area covered will be quadrupled. You are giving the textbook example of inverse square law and saying it does not apply. How much lower can you fall?
PS. I do not know what power meter you are using for your thought experiment, but it is definitely something you pulled out of your ... lets say "imagination". The real meter you would have is a light meter, which indirectly measures light density (if you know how to use it), not power.