Lanterns are dimmed by default and only shine brighter when someone walks across. Hence, two motion detectors at different heights are installed on each lamppost. As the lanterns only shine brighter when both motion detectors recognize movement, nocturnal animals can pass the lanterns at any altitude without increasing the light’s intensity. Furthermore, they are not disturbed by the additional light, as it is only emitted in the parts of the light spectrum that are visible to us humans, but not to insects.
In comparison to “energy out of footsteps”, this method utilizes more energy as the amount needed is not converted from the passing person. However, abstinence from the energy-saving variant ensures that fewer surfaces are sealed, as the motion detectors are installed on the lampposts and not on the ground.