The answer I was looking for is Portland Head. The traditional light at the top of the tower identifies the general location of the harbor entrance. This second light is a Directional Light that aligns with the main approach from offshore for large ships to safely enter the outer harbor. This light is located near ground level beside the fog signals in front of the fog-signal building and has a focal plane 23 feet above sea level. This light displays a narrow beam of three colors; white in the center, red and green on either side. It is illuminated day and night and is high intensity for day visibility with a range of 15 miles for the white and 11 miles for the red and green.
A Directional Light is a modern range light. The older range lights are a combination front light and rear light, aligned to identify the center line of the channel for which they serve. With a Directional Light only one light is needed. These lights have been and are being installed to replace the older range light combinations.
The optics are similar to that used in motion picture projectors to produce a beam with sharp cut-off boundaries between colors. When approaching this light from the right side of the channel one would see the red light only. Moving to the left, both red and white would be seen. Only white would be seen when in the center of the channel. Further to the left the light shows white and green, and green only to the far left. This light has proved to be a valuable aid for piloting large ships in and out of Portland Harbor.
Vega, Co of New Zealand manufactures these and other new design navigation lights.
http://www.vega.co.nz/default.aspx?Page=28