Understanding the Technology Behind Spectrophotometers: How Colorimeters Work

What is a Colorimeter?
Colorimeter is an instrument used to measure the color difference of objects, which can automatically compare the color difference between the sample plate and the tested object.

That is, to create a filter that simulates the spectral characteristics equivalent to the color sensitivity of the human eye, and use it to measure the light of the sample. The key is to design the spectral sensitivity characteristics of this sensor, and be able to measure and display excellent differences through computer software under a certain light source.

Based on the Lab and Lch principles of the CIE color space, it is possible to measure and display the color difference △ E and △ Lab values between the sample and the tested sample, distinguishing subtle differences between colors and achieving a degree of color consistency.

How to calculate the color difference of a Colorimeter?
Firstly, we need to know what a lab is, because the calculation of color difference in a colorimeter cannot be separated from the lab value; In 1976, CIE recommended the CIE1976 L * a * b * color space, also known as the CIELAB color space, which is mainly used for the representation and evaluation of blended colors in industries such as surface colorants.

Formula for calculating the color difference of a Colorimeters:
The formula for calculating color difference data △ E is: △ E *=[(△ L *) 2+(△ a *) 2.+(△ b *) 2] 1/2.
△ E is calculated using the formula based on the international standard color space L * a * b.
L *=measurement light source * observer angle * optical structure * sensor accuracy * sample;
A *=measurement light source * observer angle * optical structure * sensor accuracy * sample;
B *=measurement light source * observer angle * optical structure * sensor accuracy * sample;

And △ E *=[(△ L *) 2+(△ a *) 2.+(△ b *) 2] 1/2 The color difference data △ E of the Colorimeters is calculated

The color difference value refers to the size of the color difference between the product and the sample. Then we can identify the missing color through △ L, △ a, and △ b, and adjust the color quality through subsequent repairs and process optimization to achieve product color difference control.

We know that when measuring color difference, color difference is relative. Is there any color difference compared to standard colors. Then, in simple terms, this formula is (L standard color – L measurement color) 2+(a standard color – a measurement color) 2+(b standard color – b measurement color) 2.

Then, square the sum obtained from the above data. So when Δ When L is a positive value, it indicates that the tested sample is brighter than the standard sample, and when L is a negative value, it is darker. Δ When a is a positive value, the color being measured tends to be reddish (that is, the color indicated in our instrument is reddish and less green), Δ When a is negative, it is greenish with less red. Δ When b is a positive value, it is slightly yellow and slightly blue Δ When b is negative, it is blue with less yellow.

In addition to △ E, the color difference formula also includes Δ E*ab、 Δ E*uv、 Δ E*94、 Δ E*cmc(2:1)、 Δ E*cmc(1:1)、 Δ E * 00, the most common one is Δ E. Except for him Δ E * UV is also quite common. Let’s add that, Δ In the E * UV color difference formula, “U and V” represent chromaticity. The range of chromaticity values is -100 to+100. and Δ The value of E * UV is obtained from the tristimulus values of X, Y, and Z. So it is also applicable to the variance formula.

What are the functions of a Colorimeters?
1. Measurement of color matching
When a user receives a sample, they need to reproduce the same color as the sample. At this time, they need to repeatedly sample, which used to rely on human eyes to compare the differences between the small sample and the standard sample.

When within the allowable range, the process is handed over to the workshop for production. Due to subjective factors of the human eye, this difference is difficult to determine. In this case, a color difference meter can be used to measure the difference between the small sample and the standard sample, and determine whether the color difference of the sample meets the range based on the difference. This can reduce the uncertainty of human eye observation.

Here is an example:
If the color coordinates of the standard sample are:
L *=22.75, a *=22.58, b *=13.83 (i.e. (L) brightness value is 22.75, (A) red value is 22.58, and (B) yellow value is 13.83)
Set the measurement value of the standard sample as the standard, and then measure the small sample to obtain the results of the small sample:
L*=22.88，a*=20.32，b*=10.85；
Δ L*=0.13， Δ a*= -2.26， Δ B *=-2.95 (brighter 0.13, greener 2.26, bluer 2.95)

It can be seen that the next time the sample formula is revised, red (or minus green) and yellow (or minus blue) should be added. The specific degree of addition can be determined based on the experimental results, repeated several times until the color difference is within the allowable range. Experienced color mixers can determine the proportion of the formula between 2-3 times based on the value of the Colorimeters.

2. The Role of Colorimeters in Quality Control
When the product is put into production, due to changes in many factors during production, color deviation may occur in batches of products. Therefore, it is necessary to frequently use a color difference meter to measure color deviation during production to adjust the production process and achieve product color consistency.

For example, when receiving a phone case, a Colorimeter needs to be used to check if the color is qualified.
For example, plastic parts cannot be deformed or twisted (exceeding 10mm is not acceptable);
The color of the plastic parts themselves should be consistent, without impurities, color differences, etc;

Many factors often occur in production, leading to color deviation of the product. Therefore, a color difference instrument should also be used to continuously detect and adjust during the production process;
Before leaving the factory, finished products and incoming samples or color cards should be selected for testing to ensure the conformity of the produced products.

Portable Colorimeter/Chroma Meter is an innovation color measuring tool with powerful configuration to make color measurement easier and more professional; It support Bluetooth to connect with Android and ISO devices, Portable Colorimeter/Chroma Meter will take you into a new world of color management; It can be widely used to measure color value, color difference value and find similar color from color cards for printing industry, paint industry, textile industry, etc.

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