Mysteries of Light

But not too close.

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Scientists in Gaithersburg have built a large black aluminum sphere dubbed "the death star." It leaks a pale blue light on the third floor of Building 226 in the federal government's National Institute of Standards and Technology.

One could perish if trapped inside the sphere. Materials research engineer Joannie W. Chin, who helped build it, gets in every once in a while to clean it out, but only when the juice is off. There's an emergency red kill button in a clear box on a wall outside.

But the star -- technically the SPHERE, for simulated photodegradation by high-energy radiant exposure -- is seldom shut off. Using six powerful mercury lamps totaling 36,000 watts, the sphere simulates sunlight. Twenty-four hours a day. Seven days a week. For the past seven years.

Here, in Room B-349, the sun almost never sets.

The SPHERE "gives you the accelerated effects of the sun," Chin explained last week. "This device is 22 times the strength of the natural sun."

If you stuck your hand inside it, you'd get a bad sunburn. "You probably wouldn't want to do that," she said. "It wouldn't happen instantly." But if you burn on the beach in, say, half an hour, you'd burn in the sphere in a moment or two.

"It's the ultimate tanning booth," another NIST official said.

The sphere, about six feet across, was built to bombard things with ultraviolet light to see how well they hold up over time. The interior of the sphere is coated with a reflective Teflon-like material, Chin said.

One day exposed to the sphere's light is roughly akin to 35 days of normal exposure to the sun, said NIST research chemist Walter Eric Byrd.

The idea is to be able to quickly test plastics, coatings and the like without having to leave them out in the sun for weeks or months or years. "You don't want to wait 15 years to find out if your material will last 15 years," Chin said.