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Paint Color Reflection Measurements
Spectra of the Month for June investigated Color measurements using Behr paint samples obtained from a local hardware store. Behr publishes color values for their paints which were used to validate our results.
Spectra of the Month for June investigated Color measurements using Behr paint samples obtained from a local hardware store. Behr publishes color values for their paints which were used to validate our results.
Color measurements are crucial to many fields and can be applied to a wide range of industrial applications. The color module in AvaSoft produces a L*a*b* Chart to display the proper color values for identification. The CIE L*a*b* color space is a color space defined by the International Commission on Illumination (CIE) in 1976. Color is expressed as three values: L* for the lightness from black (0) to white (100), a* from green (-) to red (+), and b* from blue (-) to yellow (+). This scale was designed so the same amount of numerical change in these three values corresponds to roughly the same amount of visually perceived change of color. Some common applications for color measurements include:
A halogen light source is ideal for color measurements because of its good output between the wavelengths of 380nm-780nm, which is the wavelength range of visible light which the human eye can detect. A halogen light source used in this testing, an Avantes AvaLight-HAL-S-Mini, is connected via an SMA termination to a reflection probe. Either UV/VIS or VIS/NIR fibers are perfectly suited for this application as they are both capable of transmitting light within the 380nm-780nm range. It is important to note that the probe will illuminate and detect from the same direction, unlike an integrating sphere. If measuring iridescent or highly reflective samples where the color changes with the angle of illumination, this can alter your results and performing measurements at a 45-degree angle may be better suited for these applications. The Avantes RPH-1 is a wonderful tool to hold your reflection probe. An Avantes RPH-1 was used in this testing to stabilize our reflection probe at a 45-degree angle to measure the diffuse reflectance of our various paint samples.
A xenon source may be used for color measurements as well. However, it is less ideal as it is a pulsed light source which requires a higher averaging in order to achieve a stable output.
The reflection probe is connected to a spectrometer that is specifically configured for color measurements. This spectrometer is an AvaSpec-ULS2048L. This model features our Ultra Low Straylight configuration with a BB grating, fitted with a range of 360 nm to 880 nm. A 50-micron slit is installed on the spectrometer, along with an OSC (Order-Sorting Coating with a 600 nm long-pass filter for BB and VB gratings) and a DCL-UV/VIS-200 (quartz Detector Collection Lens made to enhance sensitivity from 200 nm to 1100 nm).
For this experiment, the Avantes software AvaSoft was utilized. Within AvaSoft, there are various modules for different types of spectroscopic measurements. One of the modules in AvaSoft is Color, which is specifically designed to collect color-related data from reflection measurements. The AvaSoft Color Application has been developed to perform color measurements with an Avantes spectrometer system and reflection setup.
In the Color module, the CIE 1976 L*a*b* color parameters are calculated, as well as other frequently used parameters, such as Hue, Chroma and X, Y, Z. These parameters can be displayed in a CIELAB chart or in a graph versus time. It’s also possible to save the measured L*a*b* values online to a database and use one of the products from the database as a reference color. Alternatively, the reference button in AvaSoft can be used to collect your reference data for your current measurement. By comparing the measured L*a*b* values with either your reference or database values, the color differences can be measured as well. Emissive color measurements can be done to measure the color of light sources, such as LED’s.
To demonstrate the capabilities of the Color module in AvaSoft, we have collected various paint samples of different colors. Four different shades of blue, green, orange, purple, red, and yellow. By using an Avantes WS-2 reference tile as our reference spectrum, we were able to successfully collect the L*a*b* values of these paint samples with our diffuse reflectance setup. Our collected L*a*b* values will be compared against the manufacturer advertised L*a*b* values to determine the accuracy of the Avantes Color module. In addition to acquiring the L*a*b* values of each sample, the reflection mode in AvaSoft was used to display a visual representation of each color measurement. The color of the spectrum line can be changed in the AvaSoft Legend to better visualize lighter and darker shades of each color.
Utilizing the L*a*b* values measured from the experiment and comparing them with the actual L*a*b* values we are able to calculate a percent difference between each color measured and actual values.
Upon comparison of the measured L*a*b* values with the actual L*a*b* values provided by the paint manufacturer, we can determine the percent difference of each of the samples. Overall, our setup was able to accurately determine the L*a*b* values for each sample with an average percent difference of 5.42% for L* values, 20.13% for a* values, and 13.68% for b* values. Some factors that could contribute to the difference between the measured and actual values could include specular reflectance, uneven paint surfaces, ambient light, or if a slightly different reference was used. Specular reflectance could alter the color reading as spectral reflectance refers to the phenomenon we see when looking at a mirror. The angle of reflection of the light is equivalent to the angle of incidence. If this light was reflected directly back at the reflection probe this could cause some discrepancies between the measured and actual values. This experiment utilized a 45-degree angle reflection probe holder to minimize the specular reflectance. If stray ambient light made its way onto the paint samples while capturing the spectrum this could alter the measured results as well. If the paint manufacturer used a slightly different color reference than the Avantes WS-2 this could slightly impact the accuracy of the color measurements as well.
In conclusion, the AvaSpec-2048L spectrometer, specifically configured for color measurements, along with the Color Module in AvaSoft can calculate extremely accurate L*a*b* values that properly match the correct color values of materials. In order to improve these readings to more accurately match the manufacture’s L*a*b* values, a reflection integrating sphere can be used in order to collect an average of a larger area of the color sample. This technique of collecting color data can be applied to a wide range of industries and fields, including lighting, medical diagnostics, food and agriculture, biology, and art and textiles. Color measurements are crucial in all industries for understanding how we perceive and react to the world around us.
