It's not the full model. What looks to you like a straight beam of light is actually not that at all. It can be refracted, which in effect curves it. Nearly all light, even laser beams, is the radiation of wave emissions from a source. The nature of waves is that they spread as they travel. A laser spreads little but it does spread. A lighthouse beam in reality is somewhat spreadier than you might think. An ocean is colder than the air above, usually. This causes the air near the ocean to be denser; the air a little above gradually less dense. This forms a lens that can bend light beams. It's like the desert mirage effect caused by hot ground and air at a different, graded, temperature.

In my case I see mirages too but it's from the cheap whiskey.