Pilot reported the airport beacon at LKU is very weak and difficult to see.

Narrative

The airport rotating beacon at Louisa airport (LKU) is very weak and difficult to see in clear weather. The condition has been reported. [Airport personnel] had the lighting system inspected and said the rotating beacon is within specifications.While on several VFR flights into Louisa over the past year or so; the airport rotating beacon is extremely hard to pick up visually. I know where it is located on the airport; and on a most recent approach at dusk it was difficult for myself and another pilot flying with me to see the beacon when we were within 5 miles of the airport setting up for entry on the downwind leg for arrival into Louisa. The beacon lighting appears dim; or the beam an incorrect angle.On this particular flight about a week ago; I was 30 miles South of Louisa setting up for our arrival at near dusk time. A small airport to the east (Bumpass/Lake Anna Airport 7W4) beacon was easily seen at that distance; but unable to see anything around the Louisa airport except for the neighboring cell phone tower lights. When we were about 10 miles south of the airport we turned on the airport runway lighting system to confirm airport location; with no beacon in sight. The Bumpass 7W4 beacon easily seen.On another flight coming into Louisa from the South East it was the same thing. Almost like flying toward a dark hole; the Bumpass/Lake Anna Airport 7W4 beacon was shining brightly; but nothing distinguishable from the Louisa airport. We turned on the airport runway lighting system to confirm airport location for the night landing. I am reporting this as an airport safety issue for all VFR pilots flying at nighttime or dusk; and possibly it should be NOTAM'd since it is so difficult to be visually acquired; and can only be seen for short distances. The beacon is also located on the water tower; which is not very high; and surrounded with tree growth. Not a good location.