The power draw of the steaming light is not much of a concern, if your engine has a charger.

I don't think powerboats are really looking for lights up off the water. I look for masthead lights, and I see them frequently, although the light usually turns out to be a plane, helicopter, star, tower or something

You can even mistake a traffic light on land for another boat

By the way, I called Sea Dog about their new LED lights C-147 mentioned above. The guy wasn't familiar with the product but eventually told me they don't make an LED stern light. I haven't been able to find this line of products for sale anywhere yet.