What is color?
Color is a trait of wavelengths of which light consists of. The human eye is capable of perceiving color of light between wavelengths of 750 and 400 nm. All wavelengths together are called the electromagnetic spectrum of which the human can only see a small portion.
This is because color is generated when objects are illuminated by electromagnetic radiation in a wavelength range between 350 nm and 750 nm. This area is visible to humans with the naked eye. The radiation with a wavelength of less than 350 nm is called UV radiation, a wavelength of more than 750 nm is called infrared radiation. These ends of the spectrum cannot be seen by the human eye.
How does a color measurement work?
Light is necessary to observe colors. We, as humans, can not distinguish colors if there is no light source present. Thus, everything would have been black. Color sensors that are used for the detection of color are equipped with an integrated light source for that reason. This light source provides steady lighting on the objects so the measured color values will always be consistent.
A step-by-step color measurement with a color sensor (also known as a spectrometer) is as follows:
1. Illumination of the measurement target
The object that has to be measured, also called the target, on forehand has to be illuminated consistently. The sensor does this with the help of an integrated light source that emits a light beam to the object. This emitted light makes a color as measurable as possible for the sensor, because a deviation in the lighting can cause color values that are off.
2. Receiving a reflection
The emitted light beam makes the object (and its color) provide a reflecting light that serves as an input for the color sensor (also known as a spectrophotometer). Thus the light that is sent out is reflected by the object and received by the sensor again. Receiving the reflected light is through the optic of the sensor. This is a special lens that varies per area of application (read more about it here) and makes the light shine on an internal color sensor. Read more about the different optic types of SPECTRO color sensors.
3. Processing the reflection
The received light reflection from the object arrives at the internal color sensor that can process it. The internal color sensor measures the color values of the received light. Next, the measured data of the values are evaluated and with the help of (spectral) sensitivity functions it is processed into color values.
4. Displaying the color value
When the measured values of the reflected light are converted into color values, these can be displayed to the user and the system in which the sensor operates. The display of measured color values is possible in a variety of supported formats such as L*a*b*, XYZ and RGB.
Industrial applications of color measurement
Different types of optics make it possible to perform color measurements in a variety of applications. Below there are a number of application in which the color sensor excels.
Colored plastic or metal parts
By using an inclination angle of 45° in the mounting of the sensor and a diffuse light beam the colors of objects with all types of shapes and (glossy) surfaces can be detected over a greater measuring range.
By suppressing the gloss, plastic foils can also be measured. To measure transparent foils, a white background is used that is placed behind the foil that has to be measured.
Narrow plastic tubes
Objects with a diameter of just 1-2 mm can be measure with the help of different optics and very small light spots (⌀ 0.3 mm) that make a color measurement in such an application possible.
Detect color difference in production
When you anodize aluminum, the chemical composition determines the final color. By measuring the color value, the consistency of the final product can be monitored. But you can also think of other applications like printed surfaces, carpet, cosmetics, food, paint, etc. Everything where color is composed.
Glazed (floor) tiles and roof tiles
A reliable measurement can be realized by optimally making use of the glossy surface and using a large measuring spot against the irregularities of the surface.
The color of the packaging material has to be measured right after the coloring of the (paper) roll. A color sensor can also measure the color of the different types of paper.
The color of a glass coating can also be measured with the help of multiple sensors that are mounted with an inclination and provide diffuse lighting. Multiple mounting angles are possible.
The color values of laminate flooring can also be measured by using a greater measuring spot and thus to guarantee the color quality within the furniture industry. The obstacle of a glossy surface can be overcome with this.
What is the best choice for your application?
It can be hard to make the right decision, because many things are to be taken in consideration in an industrial application. That's why we have a follow-up article about the different optics for color sensors and the corresponding areas of application. Still not sure or do you rather speak to an expert? Feel free to contact us!