Understanding CRI: Color Rendering Index

Date: October 13, 2016

If you work in lighting, CRI is something you hear a lot about. For those unfamiliar, it's a method of measuring how well a light source renders colors in the objects it illuminates. CRI is calculated by measuring how well the light source renders specific colors compared to a perfect incandescent light source. The specific colors measured in this comparison are given numbers that range from R1 to R14. These are called R-values, they represent 14 different hues, and they're measured on a scale up to 100. A luminaire with a high R2 value, say 94, indicates a strong presence of dark grayish yellow in its spectrum of light. Conversely, R-values can be so low that they're negative. Average the R-values, and you get Ra, also known simply as CRI.

LEDs are commonly known to emit low levels of red light. As a result, R9 value, the CRI measurement that corresponds to strong red, is often low. This is typically because white LEDs are composed of a blue LED and yellow phosphor. This mixture produces light that is blue, yellow, and the many hues in between. Red does not fall within this range, leading to its common absence in white LEDs, especially inexpensive ones.

However, by using the appropriate phosphors we are able to boost the R9 value, and make red objects appear richer and more vibrant. In doing this, overall CRI (Ra) is usually boosted as well.

Today, lighting designers typically look for CRI values above 90 alongside high R9 values. Some states, such as California, are even passing statutes, like Title 24, which make recommendations of 90+ CRI to be classified as high efficacy. To meet these emerging standards, Acolyte produces a high CRI version of every color temperature and wattage option within its white RibbonLyte series.

If you want the ability to customize your color temperature on-the-fly, and you're illuminating red objects, like rubies, or red fruit, our Variable White Red RibbonLyte offers high CRI, and rich, red tones, while not limiting you to a specific color temperature.

CRI is not a perfect measurement. Fluorescent lights, for example, often have very spiky light emissions, with only the CRI-measured colors being present, but few other hues. Nonetheless, it can be an important tool for comparing LEDs and assuring that certain colors, including deep red tones, are illuminated vibrantly. If you're looking for high CRI lighting products, ask our quotes department about our RibbonLyte options and we'll configure the custom high CRI fixture that's right for you.