Have you ever turned on a light and it's not the color you expected? Here's the deal.
Color temperature is a measurement of the orangeness or blueness of “white” light. Since white light is a whole spectrum of colors, no two whites are identical. Plus, white is relative, so our brains are always working to find it. Think about how the color of sunlight changes dramatically from noon to sunset. It’s a big shift, but we don’t often notice since it happens so slowly.
Color temperature is measured in 'degrees Kelvin' and it’s connected to the fact that the hottest parts of a flame burn blue-white, while less-hot parts burn orange-red. For example, a cloudy sky may may measure 7000K while a candle flame comes in at 2700K.
So a little confusingly, higher numbers are cooler-looking light sources, and vice-versa. In between those two extremes is a whole range of white. Two common color temperatures you'll encounter are daylight (5600K) and tungsten (3200K); you may have run in to those two settings on cameras.
In theatres with incandescent lights, purchasing lamps requires a choice between brighter/cooler ones that burn out faster or slightly dimmer/warmer ones that last a lot longer.
It’s easy to change color temperature with a gel filter—CTO and CTB (convert-to-orange and convert-to-blue) were made for that exact purpose. Tunable-white LED fixtures come with both warm and cool LEDs, so the perfect white is just a mix away. Those are extra-nice, since they could be programmed to match changing lighting conditions throughout the day or scene.
Whether you get fancy or use lights as-is, their color temperature will always be listed on the box. Personally, I like 3000K during the day in sunny locales and turn on 2700K lamps when the sun sets. Light is personal, so always do what you like, but maybe now you’ll think twice before mixing warm and cool whites willy-nilly!
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