Mammoth Hot Spring Historic District Acorn Lights Improvement Project

Side-by-side comparison of original lamps (left) and new LED fixtures (right).

NPS/Renkin/Waller

The “acorn” lights are located along the esplanade and around the parade ground in Mammoth Hot Springs. The first of these lights were installed in the 1930's when the present entrance to Mammoth from the North Entrance was formalized. Additional lamps were added in the 1960's to line the north and east sides of the parade ground. They are a contributing feature to the Mammoth Hot Springs Historic District, but not to the Fort Yellowstone National Historic Landmark. These lights provide formal landscape elements that become bright beacons at night in a small developed area surrounded by wilderness.

At the time the lights were installed there was little understanding or attention given to preserving the natural night-time environment, or how to direct light for safety and efficiency. The lights are too far apart to provide a continuously-lit pedestrian walk. Each of the 33 acorn fixtures originally carried a 175w mercury vapor lamp. These lamps were inefficient, overpowered, toxic, and were banned in the US in 2008.

The goal of this project was to improve energy efficiency of the Mammoth acorn lights by removing old technology mercury vapor lamps and replacing them with the best available technology in lighting while maintaining the historic significance of the fixtures and minimizing light pollution.

Criteria for Success

• Light fixtures remain in the same locations on the original poles and are an appropriate architectural style for Mammoth Hot Springs Historic District. 
• Fixtures are fully shielded to minimize upward light pollution that impacts the dark night sky and outward glare that is obtrusive and harmful to wildlife and humans. 
• New lamps are the most energy efficient available (LEDs), provide appropriate lumen output, light distribution, and spectrum.