What Norm created was a kind of modified slide projector, which shone three narrow beams of light across the dark harbour. A narrow white beam in the middle was flanked by beam of red to one side and a beam of green to the other. When approaching the harbour now, the captain of the boat simply had to make sure she could see the white light - if she saw red, she needed to go right, green, go left. An elegant answer to a perplexing problem.
Of course, the real trick lay in the lenses used to project the light - normally light breaks up and disperses too much to be of use, but Norm Rumsey's training and background gave him the skills necessary to solve this problem. He had worked for a while designing high quality lenses to assist in making maps from aerial photos, and could turn his expertise at lens design to the 'sector navigation lights', as they became known.