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TechTuesday

TECH TUESDAY: What is CRI?
Author: Dorothy Winslow

Thank you for joining us again! This week we’ll be talking about CRI (Color Rendering Index). This is what we talked about in the first article: “There’s also something that helps us distinguish color called CRI, or Color Rendering Index. It’s a fancy term for which colors show up in the light. The scale is 0-100, 100 being the best. If it’s lower on the scale we can’t see that many colors.”

CRI is how true an object’s color is shown under an artificial source (not sunlight). The incandescent lamp achieves 100; everything else is something less than 100. Which types of lamps have good CRI or bad CRI?

  • Incandescent has 100 (the ‘regular’ light bulbs we screw into our fixtures at home)
  • Halogen 98-100 (also lamps we screw into our fixtures at home)
  • Fluorescent 78-82 (like the ones in apartment bathrooms or in the fixtures in your supermarket)
  • Metal Halide 60-65 (the whiter parking lot lights)
  • Mercury Vapor less than 50 (used in floodlighting)
  • High Pressure Sodium less than 25 (the super yellow/orange parking lot lights or streetlights)

Here is a visual chart showing the guidelines for indoor and outdoor lighting:

CRI Chart

 

The best way I can describe how important CRI is in this example: First responders do not like the Low Pressure Sodium lighting (the super yellow/orange parking lot and street lighting) because it makes blood and oil look exactly alike (Uh-oh!).

Contrast Picture
See the difference in color rendering? LED lighting is on the left, High Pressure Sodium lighting on the right. Which feels safer to you?

 

One question I have wondered myself: How does CRI and color temperature work together? Incandescent lighting gives off a warmer color temperature but also displays a CRI of 100. How does this work? CRI is determined from the lamp’s color spectrum. Although the light is warmer, it still renders colors perfectly. Although they will look warmer in incandescent lighting than in sunlight, the same colors are still being rendered.

 

In our first article I also mentioned something called the R9 value. R9 is the red color that CRI does not include. The ability to produce a high level of Red in an LED is important for places selling products based in color (retail, furniture, draperies), for food markets (displaying meat or produce, such as apples), for museums or art galleries, and even in make-up studios for proper skin tone.
For a better illustration, let’s go back to the meat example:
“If meat is put under a lamp which does not have R9, the meat looks brown like it is already going bad. When meat is put under a lamp that has R9, it shows its natural vibrant red color (way more appetizing to buy and eat!).”

Meat comparison

Which one would you buy?

 
There is in fact a range of R9-R13 values that CRI testing does not include. You can also see in this chart which colors are included in CRI (the top 8) and which are excluded from CRI (the bottom 6):
CRI R9 Picture
Lamps with high R9 values produce the most vivid colors (as you can see from the meat example and the above chart).

 
As a reminder, if you are buying lamps or fixtures for your home, it is best to look at higher quality LED’s that include the R9 value if you are displaying collectibles or artwork. If you are shopping for lamps and are interested in what the lamp’s CRI is, look here on the label:
Label Look Up Picture

 

About the author: Dorothy Winslow is a sales associate for CES Santa Barbara and has been with the company 4 years. She specializes in LED lighting and Energy Management. She is also a San Francisco Giants fan and an avid dog lover.