data structures – Algorithm chalenge: find minimum range to cover all houses with light

N houses are located on a straight street which has K streetlights. Each streetlight has range R. Given N and K how to find minimum value for R?

N is an array containing location of each house.
K is an integer value.

I am unable to identify the algo for this. I tried solving by taking location of 1st and last house, then dividing by K, this will give me max range of each streetlight. However, assume N=[3,4,5,10,13] and K=3. With division this wont work.