In answer to your question, I'll give you distances from a central point based on different heights for the lamps.
Lamps Distance from Almaren
100 ft. 215 ft.
500 ft. 1073 ft.
1000 ft. 2145 ft.
1 mi. 2.15 mi.
10 mi. 21.45 mi. (See where this is going?
)
25 mi. 53.91 mi.
75 mi. 161 mi.
100 mi. Guess.
450 mi. 965 mi.
1850 mi. 3967 mi. (About the distance they are in the text, assuming Earth and Arda are the same.)
Let's take a look at 15 degrees, for giggles.
100 ft. 374 ft.
500 ft. 1866 ft.
1000 ft. 3732 ft.
1 mi. 3.74 mi. (I know you're surprised.)
10 mi. Really?
25 mi. 93.3 mi.
75 mi. 280 mi.
100 mi. Just Stop...
450 mi. 1680 mi.
1075 mi. 4012 mi.
Honestly, I don't really have a problem going lower than 15 degrees, closer to 10 would be fine for me as long we put a valley between to avoid having to get the light over mountains.
100 ft. 567 feet
500 ft. 2835 feet
25 mi. 142 mi.
75 mi. 425 mi.
450 mi. 2552 mi.
700 mi. 3967 mi.
EDIT: Well, that doesn't look at all like it should. For those who want to try to boil their eyes reading all that, the first number is the size of the lamps, the second, their distance from Almaren.