The relation between light and darkness relates to "direction". Light travels in all angles and all directions from the source. Shadows, however, are not omni-directional; they only travel away from a light source.
A light that only travels across or down or over or up is not any true light. It may be redirected light, but the source of light shines in all directions. The only shapes like triangles or lines that occur naturally are shadows.
Light does not discriminate, shadow-makers do. Light does not favor directions, shadow-makers do. Don't try to choose and pick so much. Just shine everywhere.