Natural sunlight is a blend of different colors and wavelengths that combine to create white light. When that light strikes a colored surface, that surface absorbs all of those wavelengths except for the wavelengths that match the color on that surface. Those wavelengths reflect back to a viewer who perceives the color accordingly. At the extremes, white objects reflect a majority of natural light and thus appear to be white, while dark objects absorb a majority of that light and appear to be black. Unlike natural sunlight, an artificial light source may not include all visible wavelengths of light, and the ability of that source to render all colors accurately, or at least as well as natural sunlight renders those colors, will be limited by the actual visible wavelengths comprising that light. How that artificial light source renders colors in relation to natural sunlight is the essence of the color rendering index (CRI) rating of that light source.
The Color Rendering Index for LED Lights
The CRI rating of an LED light source is generally more relevant than the CRI rating of an incandescent or fluorescent source because LED lights are more versatile and better able to be tuned to create specific light wavelengths that combine some or all components of visible light to render colors more accurately. CRI ratings for artificial light sources are measured on a scale from 0 to 100, with the top end of that scale equalling the full visible wavelength spectrum of natural sunlight. Thus, if you are selecting LED light bulbs for any commercial or residential application, those bulbs with CRI ratings that are closer to 100 will render colors more accurately and vividly. Most modern LED light bulbs and fixtures generate white light with CRI ratings of between 80 and 90, which creates a brighter room with lighting that is more akin to natural sunlight.
The CRI ratings of two different artificial light sources, however, cannot be compared without reference to the respective color temperatures of those sources. A light source’s color temperature is a relative measure of whether that light feels warm or cool. Light that includes a predominance of blue wavelengths can feel harsh and cold, whereas light sources with more yellow and orange wavelengths will feel warmer and more inviting. Color temperature is measured along a scale that is delineated in “Kelvin” units. Light with a CRI rating of 90 and a lower Kelvin temperature of 3000K to 400K will render objects with a warmer glow than a light source that has an identical CRI rating but with a harsher color temperature of 5500K.
LED light technology gives lighting designers a range of CRI and color temperature options that can be combined in different ways to generate unique lighting designs. Retailers who light their stores with LED’s now use this option to bring out specific colors in the products that they offer for sale and to make their store environments more inviting. Homeowners can also bend and shape LED lighting in their residences to emphasize colors or patterns in furnishings While the versatility of LED lighting has made this feasible, homeowners must also understand that they can no longer choose lights solely on the basis of a light bulb’s wattage ratings. In addition to the LED bulb’s lumen ratings (which indicates its relative brightness), the homeowner must also consider the bulb’s CRI and color rendering index in order to achieve an optimum lighting design in his or her home.
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