Enlighten Me about CRI

Q. We manufacture component parts for the automotive industry and are struggling to achieve consistent color matches. We have a small area set aside for color observation, but we still are not getting measurable results in this area. Can you make any recommendations on how we can improve? —G.G.

A. So where do you start? Many shops I have visited have a small room, painted white, with a few bright lights, thinking this is the best way to view color, but unfortunately, it is a little more involved than that. If you use a spectrometer to establish the initial ΔE (Delta E), you still need to observe and approve the finished product under proper lighting—a color observation multi light source often referred to as a light box. But the light box alone is not enough.

So how do you properly prepare a functional observation area? There are several factors to consider. It is important to understand the relationship of the lighting in and around this designated area. I am sure you have noticed that colors seem to change as you move from one area to another. This is referred to as metamerism. So how do you correct this issue? The solution involves three specific areas, which are fairly easy to implement.

First, if you have not already done so, change your lighting with the correct (CRI) Color Rendition Index. CRI is the ability of the light source to reveal colors in comparison with ideal or natural light sourcing. I typically recommend T5 light fixtures with a bulb that has at a minimum of 85 CRI, which is similar to natural daylight. The higher the number goes over 85 CRI, the closer to natural daylight it is. So, why does this matter? I have visited shops with multiple light sources such as mercury-vapor, sodium vapor and florescent, to mention a few of the more common.

Now that you know about metamerism, is it any wonder that the colors change by your orientation to the light source? For example, did you know that florescent light will make colors appear more blue, and sodium and mercury more yellow to green? Even the regular incandescent bulb you use in your home lighting can make your color appear to be more red or orange.

It would also be advisable to install the same lighting sources in the spray booth area as well. This will help the operator identify the color being sprayed against a control standard, which will save valuable production time due to rework.

Second, once the proper CRI lighting issue has been addressed, invest in a quality color assessment booth that enables you to view colors with multiple sourcing. As a general rule, these light sources should be D65, TL84, CWF, F/A, UV and U30. You did not mention it, but along with a light box, it would be beneficial to invest in a spectrophotometer. If you do not already own one, it’s an invaluable color measurement tool that works in tandem with the color light box for a total color management system.

The spectrophotometer reads the color and establishes the formula, and the light box validates the finished product. It is a good one-two punch, because the spectrophotometer takes the proper lighting into consideration when reading the initial match as this parameter is built into the software.

Lastly, there is a little-known element often overlooked in the industry that I refer to as color interference. Yes, interference… even with proper CRI lighting, and color observation equipment, you can still miss the mark. Have you ever noticed how darker or dirty walls seem to absorb good lighting? This is why I recommend that the walls around your spray booth and color observation area be painted in accordance to such standards as ISO 3664:2000 with a Munsell N7 or N8 flat to help you observe color without any bias or interference. The colors are also referred to as Standard Neutral Gray 7 or Neutral Gray 8. Munsell is not the name of the paint company, but a standard. You can Google these key phrases to locate sources for these paint colors.

To summarize, when you combine a spectrometer, light box, proper CRI lighting, and wall colors, you will achieve success in this area you have brought to light. Sorry in advance for the pun!