Some Qualities of Light That You Should Know

Before my first posting about light bulbs (sources of light) there are some qualities of light with which you should become familiar. Different sources of light exhibit different characteristics that influence which light bulb to use in different situations.

Color Temperature is a term that refers to the color of light, commonly expressed as warm or cool. Technically it is expressed in degrees Kelvin (K) with lower numbers being warmer than higher numbers. For example 1,700K is the color of a flame, 2,700K is the color of an incandescent light bulb, 3,000K-4,500K is the color temperature of fluorescent and LED light sources and 6,500K is the color temperature of the sun on an overcast day. For residential lighting purposes most color temperatures are compared to incandescent light.

Notice the smooth transition from
red to violet for the
incandescent light bulb.

Color Rendering Index, expressed as CRI, is a measure of how good colors look. All light bulbs are compared to an incandescent light bulb which is deemed to have the best CRI. CRI is expressed by a number from 1 to 100, 100 being the CRI of an incandescent light bulb. CRI’s between 82 to 100 are judged to be satisfactory while CRI’s below 80 are not. Most of the new fluorescent light bulbs, including CFL’s, are mid 80 or higher. LED’s currently range from about 65 to 88. In the photo to the left you can see the full spectrum in the light of the incandescent light bulb earning it it’s 100 CRI rating.

As humans our eyes see color as the reflection of the color in the light source. If part of the color spectrum is missing from a light source, red for example, you will not see red. Some of the early highway lighting had such bad CRI that at an accident scene the police could not differentiate between blood and oil.

There is a lot to learn about light, how we see light, how contrast affects how we see, how glare interferes with our vision and what kind of light is best for different situations. I strongly urge you to download the Underwriters Laboratory app “Light Smart” at the App Store. It has lots of great information about lighting.

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