Colorimeters are straightforward color comparison tools that are often confused with spectrophotometers. However, colorimeters have a more limited range of capabilities than spectrophotometers. What exactly is a colorimeter, and how does it work?

What Is a Colorimeter?

A colorimeter is a device that measures and quantifies emitted light from a sample. It is used primarily to identify color differences between a production sample and a known color standard. The primary elements of a colorimeter include:

  • Illuminant: A controlled light source used to illuminate the sample being measured.
  • Tri-stimulus absorption filters: Red, green and blue (RGB) filters which quantify the emitted sample light in the form of tri-stimulus values, which replicate the human visual response to color.
  • Display: Presents the data in the form of industry standard color scales and color differences.

Colorimeters may be tiny and portable for usage on the road or bigger for benchtop use in a lab.

How Does a Colorimeter Work?

The colorimeter illuminates the sample being measured using a controlled light source. The light not absorbed by the sample is ‘emitted’. This light is what we see as the color of the sample. This emitted light is compared to an established standard for pass/fail determination.

The colorimeter's lens and tristimulus absorption filter converts the light beam into an isolated wavelength. The photocell measures how much of the wavelength was absorbed and displays the data on its digital display. Colorimeters and spectrophotometers are among the most advanced color-measuring tools. Although closely linked, they each have distinct qualities that make them best suited to specific measurements.

A tristimulus colorimeter is an essential tool for objective color measurement. It consists of three fundamental components:

  • Light source: The initial lighting is provided by a steady light source, usually a bulb with a consistent voltage.
  • Filter system: The filter system consists of a collection of three filters. Each filter transmits a specific wavelength, allowing for selective study of the reflected light from the sample.
  • Photoelectric detector: This detector transforms the intensity of emitted light into an electrical signal. The electrical output matches the sample's color attributes. 

Ideally, the combined response of the light source, filters, and detector should closely resemble the spectrum sensitivity of the human eye to a certain illuminant. Getting a perfect match between the instrument response and human eyesight is difficult. However, high-quality tristimulus colorimeters provide an accurate approximation. Notably, the mismatch occurs often in the short-wavelength band. Mathematically modifying the measured blue value (Z) in proportion to the green value (Y) creates a more accurate total value.

Because the instrument's response might vary over time, it is critical to calibrate it regularly according to manufacturer’s recommendations. Modern colorimeters generate digital outputs that may be automatically translated into industry standard color values such as CIELAB (L*,a*,b*) or CIELCH (L*C*h*) systems. 

What Are Colorimeters Used For?

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Colorimeters are commonly used for comparative color quality controlmeasurements in a wide range of industries to determine pass/fail, including:

  • Calibration of displays and computer monitors.
  • Automotive interior assemblies. 
  • Food applications.
  • Ensure accurate quality control in color printing, textile production, and paint manufacturing.

Colorimeters do not provide full-range spectral data, so they are better suited to applications requiring faster results with less analytic depth.

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Colorimeter vs. Spectrophotometer

There are many critical differences between colorimeters and spectrophotometers. One significant distinction is that spectrophotometers are more versatile with multiple illuminant and observer combinations and several geometric arrangements. The precision optics of a spectrophotometer collect the light that reflects off of or is transmitted through a sample. The spectrophotometer can then calculate the exact number of photons at specific wavelengths and determine the three-dimensional coordinates of the object's color.

A spectrophotometer measures reflectance and transmittance for the entire electromagnetic spectrum, while colorimeters operate only in the visible portion. Spectrophotometers can also measure qualities that colorimeters can't, such as metamerism, a phenomenon where one color may look different when viewed under different light sources .

Because spectrophotometers offer full-spectrum analysis, they are ideal for a wide range of applications requiring tight tolerances, particularly in research and development stages where specialists can use them for color system development and color formulation. They are also perfect for providing quality control during production.

Color Solutions From HunterLab

HunterLab has been a leading innovator in color measurement solutions for more than 65 years. Browse our full line of spectrophotometers to find the perfect tool for your application, or contact us with any questions.