Spectrophotometers
Color and Appearance can be quantified with the right instrument. The applications are wide ranging from consumer products to food, fashion, paint, and more. TEquipment offers a variety of instruments to meet these needs. First let’s understand more about each instrument and its applications. At the end there will be a brief tutorial on color. You can learn more about color from
Precise Color Communication by Konica Minolta. It is the reference used in this article.
What is a Colorimeter?
A Colorimeter quantifies color. Colorimeters have sensitivities corresponding to those of the human eye, but because they always take measurements using the same light source and illumination method, the measurement conditions will be the same, regardless of whether it’s day or night, indoors or outdoors. This makes accurate measurements simple.
Color Control of Textiles
Minute color differences are the biggest headache anywhere that color is used. But with a colorimeter, even minute color differences can be expressed numerically and easily understood.
Key Features of a Colorimeter
- Built-in Light Source. Ensures uniform and consistent illumination
- Constant Illumination/Viewing Angles
- Constant “Observer”. The “observer” of the colorimeter is a set of three photocells filtered to closely match internationally adopted color standard (Standard Observer).
- Elimination of Area Effect Ad Contrast Effect. Since the colorimeter measures only the specimen (provided the specimen is at least the specified minimum size), the effects of different specimen sizes or backgrounds are eliminated.
- Color-Difference Measurement. Color difference from a target color can be measured and instantly displayed in numerical form.
- Data Memory and PC Communications
What is a Spectrophotometer and How does it differ from a Colorimeter?
1. Spectral Reflectance. Subjects measured with a tristimulus colorimeter can only obtain numerical color data. If a Spectrophotometer is used, not only can the same types of numerical data be obtained, but also the spectral reflectance graph for that color. Further, with its high-precision sensor and the inclusion of data for a variety of illuminant conditions, the spectrophotometer can provide higher accuracy than that obtainable with a tristimulus colorimeter.
L*, a*, b* Same results as colorimeter but additional
insight of spectral reflectance and wavelength region
A tristimulus colorimeter measures the light reflected from an object using three sensors filtered to have the same sensitivity as the human eye. On the other hand, the spectrophotometric method utilizes multiple sensors to measure the spectral reflectance of the object at each wavelength or in each narrow wavelength range. The instrument then calculates the tristimulus values.
2. Spectrophotometers provide high accuracy and the ability to measure absolute colors. They are typically larger, more expensive, and less portable than colorimeters, so better suited in research and complex color analysis. Colorimeters are better suited to production and inspection applications for the color difference measurements and color chart comparisons.
3. Spectrophotometers can spot Apparent Color change. Color changes depending on the source light. A relatable experience is looking at clothing in the department store lighting versus outdoors. In order to quantify color, the industry has defined Standard Illuminants for daylight, fluorescents and more. Colorimeters have a built in light source to standardize the reported measurements. A spectrophotometer actually measures the spectral reflectance of the object. The instrument can then calculate numerical color values in various color spaces using the spectral power distribution data for the selected illuminant and data for the color-matching functions of the Standard Observer.
4. Spectrophotometers can handle Metamerism. Color depends on the light source. A related problem is the color difference that can occur between two seemingly identical objects viewed together in different light sources. For example, two hand bags viewed outside look identical but viewed under indoor lighting look different. This problem is often due to use of different pigments or materials. Looking at the spectral reflectance curves from a spectrophotometer will spot the difference immediately, while a colorimeter would report the same color for both objects.
Key Features of a Spectrophotometer
- Illuminant Conditions. data for a wide variety of illuminants (light sources) are stored in memory to allow meassurement results to be calculated under various illuminant conditions
- Fixed Illuminant/Viewing Angles. The illumination/viewing geometry is fixed to ensure unform condisions for measurements
- Spectral Sensor. Spectral sensor consisting of various segments to measure light at each wavelength interval for high accuracy
- Color Spaces. Measurement data can be displayed numerically in a wide variety of color spaces, including Yxy, L8a*b, Hunter Lab, and other formats
- Color-difference Measurement and Graphing. Color difference from a target color can be measured and instantly displayed in numerical form or on a spectral reflectance graph
- Data Memory and PC Communications