The illumination at a point is inversely proportional to the square of the distance of the point from the light source and directly proportional to the intensity of the light source. Suppose two light sources are $s$ feet apart and their intensities are $I$ and $J$, respectively. Let $P$ be the point between them where the sum of their illuminations is a minimum. The distance of $P$ from light source $I$ will be feet. (Your answer will depend on $I$, $J$, and $s$.)