Color & Lights

Color temperature is measured in degrees Kelvin (K). The color temperature of a lamp (bulb) describes how the light appears when the human eye looks directly at the illuminated bulb.

Color temperature is measured by a unit called the Kelvin (K). The Kelvin temperature scale is defined so that absolute zero is 0 kelvins (K). (The Celsius and Fahrenheit scales are defined so that absolute zero is −273.15 °C or −459.67 °F). Imagine heating a bar of steel and observing the color of the bar at increasing temperatures. At some point the bar will appear to glow a dull red. As heat is added, the dull red turns to yellow, then to white, then to bluish white, finally to blue.

A light bulb that produces light perceived as yellowish white will have a color temperature of around 2700K. As the color temperature increases to 3000K – 3500K, the color of the light appears less yellow and more white. When the color temperature is 5000K or higher the light produced appears bluish white. The color temperature of daylight varies, but is often in the 5000K to 7000K range.

When deciding on the best light bulb for a particular application, one consideration not to overlook is the appearance of the light as perceived by the people using the space. For example, many people will find a formal dining room more appealing with “warmer” appearing light, while for a large, open-plan office “neutral to cool white” appearing light is the better choice. Color temperature designations of light bulbs can be confusing. Sometimes you’ll see subjective terms such as “warm white” or “cool white.” Other times, the quantitative Kelvin temperature number will be used: 2700K (warm white), 4100K (cool white). Here are some approximate reference points: candlelight is 1800K (warm yellow), a standard 60W incandescent light bulb is 2700K (warm white), lights in a portrait photo studio are 3200K (neutral white), fluorescent lights in a classroom or office are often 4100K (cool white), daylight with a thin overcast sky is 6500K (bluish, white light). Most incandescent and halogen bulbs are in the Kelvin range 2700K-3000K. Fluorescent, metal halide and LED bulbs can be purchased with color temperature options from 2700K to 6500K.

The colors of Spring are a reminder of how important color is in our lives. The subtle color variations of a flower blooming in the yard on a clear day can easily be seen and appreciated. The same flower in a vase at the office might not look quite as colorful. Why? Because it is the light source illuminating an object that determines how well humans see color.

CRI, or color rendering index, is a numerical scale (0 to 100) used in lighting to indicate how a light source will make the color of an object appear to human eyes. The higher the number, the better the color rendering ability.

In many cases, this difference is not important. However, for certain applications such as illuminating tones within the hair, CRI can make all the difference. There is also evidence that high CRI bulbs might be perceived to be brighter which could allow for the installation of lower wattage bulbs to save energy. Topbulb offers high CRI lighting options for fluorescent, halogen and metal halide bulbs.

All incandescent and halogen light bulbs, by definition, have a CRI close to 100. They are excellent at rendering color. However, except for some halogen bulbs, most incandescents produce a warm 2800K color temperature. The only way to achieve the bluish white appearance of daylight with incandescent bulbs is to use bulbs coated with neodymium. However, these bulbs have a CRI much lower than 90. They are not good for accurate color rendering across the spectrum.

This is why hair appears different colors under different lights!

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