Color Matching - Spectrophotometers

If you’ve ever attempted to visually match a paint color with a fan deck from a paint store, you know it’s nearly impossible to get a close match. You would think that matching a simple neutral color in your house would be easy until you find dozens of beige variations in the fan deck. So what do painting contractors do when they need to match a color?

Spectrophotometers are common in research labs for physics, biology, and chemistry, but they are also used in paint stores to match colors. So how does a spectrophotometer work?

To understand how it works, you have to understand what color is. Color is made up of wavelengths of light. The visible light spectrum is red, orange, yellow, green, blue, indigo, and violet (Roy G. Biv). Black is the absence of color. White is made of up all these colors.

The spectrophotometer is a small device with an illumination source, interference filters, photodiode, and readout device. White light (remember that white is all colors) is used as the illumination source in the form of a tungsten bulb or LED. A sample is flooded with white light. The light is reflected off the sample into the machine and onto a small wheel. The wheel consists of a number of interference filters and is powered by a stepper motor.

Visible light wavelengths are measured in nanometers and each filter is programmed to allow a specific wavelength of light pass through it. Essentially, through the process of elimination the filter passes the information to a photo diode. The photo diode in turn converts the information into an electronic signal which can be sent to computer with software to match the base and the amount of pigment needed.

These machines can match a variety of samples. At Beach Painting we will typically remove a paint sample off of the substrate we are going to match, but fabric samples, wallpaper, and carpet samples can also be used in a spectrophotometer.