Physics Photo of the Week

March 3, 2006

Full Cutoff Light Fixtures

Through an arrangement with Progress Energy - the electric utility company that serves the Asheville, NC area - full cut-off exterior lighting has just been installed.  This is a step in saving energy.  Traditional exterior lighting uses a diffuser that extends below the fixture and sends light in all directions: down, sideways, and up into the sky.  The modern fixtures have been designed so that the light output from the fixture is only directed down where it is needed, not sideways and not upward.  Note that the window to emit the light is flat and flush with the fixture.  The source of light is completely enclosed in the fixture, thus preventing light from escaping in the unwanted directions. 

These full-cutoff fixtures are a partial answer to light pollution.  Excessive stray light is blocked by the cut-off design from lighting up the skies.  The cut-off design thus prevents some of the urban glow radiating into the skies and making stars and planets next to invisible for anyone living near an urban environment.  They are also more effecient at doing the job of lighting the ground where the light is needed.  Compare the night-time illumination effectiveness of one of these new fixtures (below left) with the traditional non-cut-off fixture (below center).  Compare the full cut-off shielding of the new fixtures (Photo above) with the design of a traditional fixture (below right) that sends the light in all directions rather than down where it is needed.  The new fixtures consume the same wattage as traditional fixtures, but are more efficient at lighting and preventing light pollution and wasted energy.

Illumination from a new fixture

Illumination from a traditional fixture

Traditional fixture that is not shielded.  This is the same fixture as the center photo.

Full cut-off exterior lighting is now regularly installed in many new shopping centers.

Our thanks go to
the Campus Greening Crew: Amanda Davis, Julia York, and Liina Laufer under the supervision of Jessica Wooten and  Stan Cross; Greg Sterken of Progress Energy; and WWC Facilities Director Paul Braese for their work researching the replacement of the traditional pole lighting with the full cut-off fixtures.  May dark skies prevail!

All Photos by Donald Collins

Physics Photo of the Week is published weekly during the academic year on Fridays by the Warren Wilson College Physics Department.  These photos feature an interesting phenomena in the world around us.  Students, faculty, and others are invited to submit digital (or film) photographs for publication and explanation.  Atmospheric phenomena are especially welcome.  Please send any photos to

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