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Earth Sense: Colors result from surfaces reflecting available light
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Colors change with the light. This was an issue recently when a friend was having a vintage Porsche repainted, and the shade of ivory just didn’t look right.

I glanced at the overhead fluorescent tubes and suggested we push that 1965 gem outside. Shining in the bright Clarkesville sunlight, the paint job suddenly looked exactly right. 

Painted surfaces get their color from reflecting available light, and fluorescent tubes are some of the worst light sources for judging. Their colors vary from a dull green to pink to “cool white,” which is probably closest to daylight but still no match.

It gets even more difficult when you’re trying to match an image on a computer monitor to a real object. The monitor emits its own light, using what physicists call the “additive color spectrum.” All the colors add up to white. But surfaces reflect in the opposite sense, the “subtractive colors.”

The more color is added to an object, the darker it tends to get.

Human skin, and metals such as gold can’t be shown in true colors on a screen because “brown” (skin) and “gold” don’t exist in the additive spectrum. This is why early color TVs showed everybody in an orange glow until the technology became more fine-tuned.

Sunlight changes colors, too, depending on the time of day. Noontime on a dry day is the worst period to take pictures of people. The deep blue sky will throw ugly blue patches on their faces.

In the late afternoon, the sun’s rays take a much longer path through the atmosphere, which filters most of the blue out. This favors the red part of the spectrum and produces the rich, warm colors we consider more pleasant. 

LED bulbs, the latest in home lighting, offer a variety of choices. Packaging often shows their “color temperature” in degrees Kelvin. In a simple way of speaking, it’s the color a chunk of black iron takes when heated to that temperature.

One might instinctively pick “warm white,” about 3,500 degrees Kelvin. But try the “cold white” (6,500 K or more), which puts a realistic daylight color into the house. It seems blue at first. But if the bulbs are bright enough, you may come to enjoy the “daytime” look of the rooms, and not want to revert to the yellowish tint home lighting had in the past.

Rudi Kiefer, Ph.D., is a professor of physical science and director of sustainability at Brenau University. His column appears Sundays and at gainesvilletimes.com.

 

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