Capitol Illumination

As I've walked in the dim pre-dawn light up to the Capitol during daylight saving time, I've crossed paths with scores of my Architect of the Capitol (AOC) colleagues as they head home after a full night's work. These AOC employees work each night to get the buildings of Congress and the Supreme Court ready for another day – by cleaning, repairing and maintaining them – without interfering with the work of these institutions.

While I pass my colleagues on the sidewalk walking up the hill, I watch the stars disappear from the sky as the sun's light brightens it. This week, I've also watched as the lights that illuminate the Capitol Dome at night shut off, leading me to wonder about why they're turning off at that moment, and who's making it happen.

The AOC Office of the Chief Engineer had answers to all my questions. They told me about the history of lighting in the Capitol, around the Capitol and the lighting of the Dome.

In the past, the exterior and even interior of the Dome were lit only during rare night sessions of Congress, for special occasions or holidays. Today, however, the exterior of the Dome is lit from dusk to dawn, every day of the year. These lights come on automatically, with the timing controlled by an astronomical time clock located in the basement of the Capitol. The lights that shine on the great fresco Apotheosis of Washington inside the Dome and illuminate the grounds around the Capitol are also controlled by that clock.

The exterior lights allow you to see a circle of columns at the very top of the Dome known as the tholos, which holds the Statue of Freedom above the Dome. Inside the tholos is what is called a convene or session light. Traditionally, it's been lit at night to signal that either the House or the Senate, or both, are in session.

When the Capitol was built, there was no reliable supply of artificial light, so the building includes skylights, cupolas and even interior light wells to provide natural light to the many rooms within. Any original lamps first burned candles or whale oil – replaced in the 1830s by kerosene, which wasn't as smelly and sooty. In the 1840s, kerosene was replaced with the newest form of fuel: natural gas.

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One remarkable feature of the Capitol's original Bulfinch Dome in 1847 was the sight of Crutchett’s Lantern, a gas lantern which included reflectors that threw light into the Rotunda at night and could be seen miles away.

This culminated in the hanging of a gas lantern that was 6 feet wide and 20 feet tall from a 100-foot-tall pine mast atop the old wooden Dome of the Capitol, which started the tradition of placing a light at the highest point of the Capitol.

Even after the introduction of electric lights, they weren't consistent enough in quality to replace gas lighting until the late 1800s. The first incandescent lights in the Capitol were installed in 1885, near the Senate Chamber, and they quickly replaced all the gas lights, so that by 1898, almost all of the Capitol was lit by electric lights.

In 1905, the Washington Times reported that on the evening before Teddy Roosevelt's inaugural ceremony, "four powerful naval searchlights poured tremendous candlepower upon the Dome," although it was still not regularly lit. For the second inauguration of Woodrow Wilson in 1917, there is a report of the Dome exterior being lit by electric floodlights, and in August of that year, it was decided that the Dome should be lit every night until midnight to "inspire the patriotic sentiment of visitors and troops passing through the city."

The practice continued through and after World War I, with advances in technology allowing smaller, more efficient floodlights to be used. There were other reasons to continue lighting the building, such as making it visible to small planes, which were became more common after American aviator Charles Lindbergh crossed the Atlantic.

During World War II, however, the Dome was again blacked out from December 1941 through May 1945. In 1990, the lights were again updated; 60 incandescent fixtures were replaced by 38 high-intensity discharge (HID) fixtures. The new lights greatly reduced the maintenance time due to the long life of the new metal halide lamps and they reduced energy usage by 45 percent.

I'm impressed by the improvements the AOC has made throughout history to illuminate the Capitol for those who work in it and those who visit and view it from outside. As I learned, there's far more than meets the eye in the lighting of the Capitol, from the clock in the Capitol basement to the modern light fixtures hidden on the roof of the building.