What about light Quality?

A good energy efficient light fixture not only needs to provide enough light, but also good quality of light! How do we measure light quality? Two terms that you will come across on light quality: Color Temperature and Color Rendition.

Color Temperature – refers to the color of the light source. By convention, yellow-red colors (like the flames of a fire) are considered warm, and blue-green colors (like light from an overcast sky) are considered cool. Color temperature is measured in Kelvin (K) temperature. Confusingly, higher Kelvin temperatures (3600–5500 K) are what we consider cool and lower color temperatures (2700–3000 K) are considered warm. Cool light is preferred for visual tasks because it produces higher contrast than warm light. Warm light is preferred for living spaces because it is more flattering to skin tones and clothing. A color temperature of 2700–3600 K is generally recommended for most indoor general and task lighting applications.

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Color Rendition - refers to how colors appear when illuminated by a light source. Color rendition is generally considered to be a more important lighting quality than color temperature. Most objects are not a single color, but a combination of many colors. Light sources that are deficient in certain colors may change the apparent color of an object. The Color Rendition Index (CRI) is a 1–100 scale that measures a light source's ability to render colors the same way sunlight does. The top value of the CRI scale (100) is based on illumination by a 100-watt incandescent light bulb. A light source with a CRI of 80 or higher is considered acceptable for most indoor residential applications.

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As shown in the above imagine, the very low CRI of 40 makes this lady in the above photo looks like a dead person as opposed to how vibrant she looks under a CRI of 100.

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Notice how vibrant and distinct colors of fruit and vegetables under CRI of 91 fade when CRI decreases to 70.

What CRI is needed for the job?

It depends! Each type of industry requires different quality of lighting. For example, Midwest Fiber - a local storage company doesn't require very good quality lighting. A CRI of 70 and above might be sufficient.

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On the other hand, a printing facility - Bloomington Offset Printing Inc. where inspection of the quality of the finished product needs color to be rendered accurately. Higher CRI becomes essential in this facility. Note the person in yellow is checking to make sure that color from the printing press matches customers specification.

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What do you think CRI requirements for jewelry stores and art museums?

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High CRIs! In a jewelry store, sales depend on the looks! CRI has to be high to show the beautiful sparkly colors of jewelry. In a museum, high CRI is essential to show the beauty of arts. Even in a residential home, we can use high CRI light fixtures in parts of the room where you want to show the beauty of your treasures.

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Have I Grasped the Key Concepts Here?

 

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Color rendition is generally considered to be a more important lighting quality than color temperature

 
 

 

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alternative accessible content What CRI should be used for each job?
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