Note that these are all estimates and averages. Different bulbs produced with different materials and with different techniques will vary widely in their color temperature. Professional lighting like that used by photographers and filmmakers can vary well beyond this narrow range and can even mix various colors of lights together in a single device.
The use of the terms "warm" and "cool" is a bit paradoxical because, when examining the Kelvin scale, you'll see the "cool" light is actually hotter than "warm" light. The terms warm and cool aren't intended to describe the actual temperature of the flame used to produce the light but rather the aesthetic these lights generate. As well, color temperature ratings aren't always entirely meaningful on their own. The color temperature of the sun is measured at about 5600K, but the actual sun itself varies in temperature widely (and reaches into the millions of degrees internally). It is only the visible portion of the energy emitted by the sun that we detect as light that approximates its color temperature rating.
Matching color temperature to your environment
If you've ever replaced an incandescent light bulb with a fluorescent bulb and remarked about how cold, off-putting, or downright ugly the room looked after your upgrade, you've experienced how dramatic an impact color temperature can have.
Everything in a room is impacted by the light source in that room. A wall that is white under a 3200K light source can look green under a 4000K light source. That same wall under a 2500K light source may look yellow. This is why designers advise you to place lighting elements and choose bulbs before you paint and furnish a room. "The color paint you pick under the fluorescent bulbs at a hardware store might look very different when you get it under the light bulbs you have at home," says Cory Bergeron, an author and video production professional.
The appearance of your room aside, the color temperature of your light can have some subtle and not-so-subtle effects on the way you live and work.
Danyelle Kukuk, director of product and category management for Batteries Plus Bulbs, says that bulbs that mimic daylight (in the 5000K to 6500K range) are increasingly popular in a variety of rooms. She notes, "Some customers appreciate having daylight lamps in their bedrooms because the color of the light, mimicking daylight, helps them get moving much quicker in the morning than the warm, cozy soft-white lamps.
Also, many of the reading lights on the market are daylight temperature, as the color provides great contrast between black type on white or off-white paper, making it easier on the eyes to read." Kukuk also says that daylight bulbs are popular in bathrooms, because they make it easier for women to see what their makeup will look like outdoors.
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