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The devices, known as pyranometer, measure the amount of solar radiation — or energy — that reaches the surface of the earth each day.

That date went down as one of our darkest days so far this century, according to scientists who use a device called a pyranometer to study the strength and weakness of the sunlight that reaches ground level.

You don’t need a pyranometer to track the depths of our lightlessness, though.

As David installs a pyranometer, which measures solar radiation, their conversation touches on global warming.