Range of lighthouse on Chanonry Point

Having noted that I could see lights on an oil rig that I worked out was 10 miles away, I wondered about the nominal range of this lighthouse as being 15 nautical miles. I've been trying to find out the power of an LED replacement bulb but that's hard because it is less electrical power for the same brightness as an old-fashioned bulb. I found a similar lighthouse that used to have a 250 Watt incandescent bulb. I was going to do an inverse square law calculation based on this power but the problem is that 250W of electrical energy in does not mean 250W of light energy out. It has taken me into territory about human perception of light that involves lumens. More research needed.