Colorimetry is a measurement method that quantifies the color of an object by measuring the intensity and wavelength of light absorbed, transmitted, or reflected by a sample. Usually represented by RGB (red green blue), it can also be represented by HEX and L * a * b *.

The L * a * b * color space was originally defined by the International Commission on Illumination (CIE), where L * defines the brightness from black (0) to white (100), a * defines the brightness from green (-128) to red (+127), and b * defines the brightness from blue (-128) to yellow (+127). Any unit change in L * a * b * corresponds to a visually perceived color change.

This experiment aims to measure the L * a * b * color space values of 13 different paint samples, including two purple samples ("Blue Ash" and "Merlin Robe"), two brown samples ("Deep Soil" and "Gondola"), three white samples ("Polar White", "Tooth White" and "Summer Grey"), and six green samples ("Clover", "Mint", "Cool Blue Grass", "Green Water", "Phoenix Tears" and "Mint Mist"). The white reference tile will be used as the white reference material, and measurements will be conducted within the visible (VIS) spectral range.

The spectrometer used in the experiment isAvaspec-ULS2048CL-EVOAs a universal spectrometer, it can be used not only for absorbance measurement and reflectance measurement, but also for color measurement. It uses our powerful AS-7010 circuit board and provides USB 3.0 communication interface, with data transfer speed 10 times faster than USB 2.0.

The light source used in the experiment isAvaLight-XE-HPA high-power pulsed xenon lamp light source with a power of 6W. This light source has a small size and is very suitable for integration into the system.

Other attachments used in this experiment: white reference tile (WS-2), used as a white reference for reflection measurement and color measurement; A 200 micron fiber core reflection probe (FCR-7UVIR200-2-BX) is used to connect an integrating sphere and a spectrometer; Probe holder (RPH-1), keep the probe at a 45 degree angle; And a specially designed interface cable that can connect AvaLight XE-HP to AvaSpec-ULS2048CL-EVO to control scanning flicker and power the light source.

All samples are paint samples sold in hardware stores, stored in a drawer to prevent color changes due to sunlight exposure. The reflection probe is installed on the bracket, placed separately above each paint sample and kept at a certain measurement distance from the sample. We maintained the same distance when measuring the white reference tile to ensure consistency in the experiment.

The data analysis module uses two modes from AvaSoft, a customized software package from AVANTES.

The first mode is the color measurement mode, which is included in AvaSoft Al or as a single module. This mode is designed specifically for color measurement and can measure parameters such as L *, a *, b *, X, Y, Z, as well as dL, da, db, and dE. The measurement chart displays the sample L * a * b * in real-time and can also configure separate reference colors for dL, da, db, and dE measurements. All data can be saved to Excel or text documents.

The second mode is reflectance measurement mode. This mode is designed specifically for reflective applications. This experiment uses white reference tiles as the white reference. We set the integration time to 50ms, the average number of times to 10, and the flicker frequency of each scan of the light source to 5 times (the integration time can be adjusted to increase or decrease the amount of light measured once and affect the overall size of the resulting spectrum. The average number of times to 10 indicates that the obtained spectral value is the result of averaging 10 values together, which can make the spectral result more consistent.)

The following text lists the spectra of the samples in Scope mode, the reflectance spectra of the samples, and the data of each sample in color measurement mode.

The reflectance mode provides much richer spectral information. White samples have high reflectance in the visible spectrum, while green samples have reflectance ranging from medium to low in the visible spectrum. However, reflectance increases in the green region, purple samples have higher reflectance in the blue purple region, and brown samples have low reflectance in the visible spectrum (Figure 5).

The L * a * b * color space values for each sample are shown in Table 1.

The L * value of the purple paint sample is relatively low, indicating that its brightness is dark. A positive value for a * and a negative value for b * indicate that they are a mixture of red and blue, resulting in purple.

The lower L * values of brown paint samples indicate that they are darker than purple samples. A value close to zero indicates that the mixture of green and red is very uniform, while a positive b * value indicates that the sample has more yellow than blue, which are accurate descriptions of typical brown.

The range of L * values (40.46~79.52) and b * values (-0.53~16.3) for green paint samples is wide, but the a * values for all samples are negative (-9.77~-40.8). These negative a * values indicate that there are more green than red in each sample.

Finally, the white paint samples all showed high L * values close to 100, indicating high brightness, with a * and b * values close to zero, indicating uniform mixing of green, red, blue, and yellow, which is consistent with the fact that white is a combination of all colors in the visible spectrum. The b * value of tooth white is slightly higher, indicating that it is slightly yellowish compared to the other two white paint samples.

This experiment uses AvaSoft reflectance measurement mode and color measurement mode. The reflectance measurement mode provides a broad spectrum concept of the sample, while the color measurement mode provides quantitative values in the L * a * b * color space.

The spectrometer used in the experiment is AvaSpec-ULS2048CL-EVO, which has a wide range of applications and is suitable for measuring absorbance and reflectance, as well as color measurement as shown in this experiment. The light source used in the experiment is AvaLight XE-HP, which is suitable for high-power or integrated applications.