The following photo was taken by Razorlux of three identical desk lamps with the same wattage spiral CFL bulb only in three different colors (2700K, 4100K and 6500K). Notice that the true life colors match the diagram above.
The Range of Color Temperature. The three primary types of color temperature for light bulbs are: Soft White (2700K – 3000K), Bright White/Cool White (3500K – 4100K), and Daylight (5000K – 6500K). The higher the Degrees Kelvin, the whiter the color temperature
Northern Sky: 8000K
A clear sky producing a blue color light outside of the range of currently available light bulbs.
Overcast Sky: 6500K - 7500K
Slightly blue light shines during an overcast sky. You may have see "Daylight" bulbs, which are included at the low end of this Kelvin temperature range.Above 4500K brings us into the “daylight” color temperature of light. Light bulbs (lamps) with color temperatures of 4500K and above will give off a blue-white light that mimics daylight.
Sunlight at Noon: 4000K - 6500K
The whitest natural light occurs when the sun is directly overhead. The closest light bulbs will be in the "Daylight" range on some packaging. You now know that this is the 4000-6500K range for fluorescent bulbs.Color temperatures between 3100K and 4500K are referred to as “cool white” or “bright white.” Light bulbs (lamps) within this range will emit a more neutral white light and may even have a slightly blue tint.
Incandescent and Halogen Bulbs: 2500K - 3500K
Commonly found in lamps and fixtures in your home and office. These bulbs produce light with a yellow tint. CFL bulbs can produce light in this light range (lower K rating).At the lower end of the scale, from 2000K to 3000K, the light produced is called “warm white” and ranges from orange to yellow-white in appearance.
Candle Light: 2000K
Candles burn a soft yellow light. One lumen is the amount of light produced by a single candle.
CRI or Color Rendering Index
The CRI is the measure of the ability of a light source to reproduce colors of various objects compared to an ideal light source such as incandescent (only because it's what our eyes are used to) or natural light. The scale is from 0-100, and those lights with a CRI closer to 100 have an ability to show truer colors across a wide spectrum. It's important to consider for some applications, but definitely not for all. For example, it's very important in a retail store to have lights with a high CRI, so that colors appear as they truly are. Whereas in a factory (CRIs often in the 70s or 80s), or with street lamps(CRIs in the 30s or 40s), color accuracy isn't nearly as important as the overall amount of light produced; or lamp cost.
The Future of Color Temperature
Currently there are color tunable LED’s on the market, but they are not affordable and are generally used for high end projects. As they become more affordable, lighting in the home and office will change color temperature based on the time of day and setting. This will help simulate day/night cycles.
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