Understanding Color Temperature Continued

30,000°K depending on the time of day, the month of the year, latitude, altitude, and atmospheric conditions. For instance, sunrise (or sunset) can be 2,000°K. One hour later it might go up to about 3,500°K. Noontime summer skies in Washington, D.C., average about 5,400°K. (Source: Kodak.com)

Similarly, unless your lights are rated and guaranteed for a specific color temperature, their values will vary. So, all we can talk about are average color temperatures in typical lighting situations. Incandescent tungsten light bulbs are generally about 2,600°Kto 3,200°K (depending on the wattage), and typical inexpensive office fluorescents are about 4,000°K. Candlelight, incidentally, is about 1,800°K.

To make things even more complicated, light bulbs can age, and their color temperatures usually decline as they get older. In addition, electrical current fluctuates and can influence how hot or cool a light bulb burns. So, a 3,200°Ktungsten bulb might dip periodically to 2,800°Kor peak as high as 3,400°K, and it can change second by second. That's why photographers use line stabilizers and power conditioners to keep the voltage constant, so color temperature won't vary during their shoot.

In DigitalBenchmarks Lab, we use special (and very expensive) full spread spectrum nonflicker 5,000°K Kaiser fluorescent lights on line stabilizers and power conditioners for our simulated daylight setups. Even so, we measure their color temperature before, during, and after all test shoots. If the color temperature is slightly outside our normal parameters, we usually wait for the bulbs to warm up some more. If the variation still persists, we replace the bulbs.

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