Color measurements of objects and thick fluids can be done using a spectrometer, light source and either a reflection probe or an integrating sphere. A spectrometer is needed with a wavelength range from 380 to 780 nm and a spectral resolution of 5 nm FWHM. Further a white continuous light source is needed as well as a white reflective tile. For the different applications different probes can be used. A typical setup for color measurements in reflection is given below.

Components used in the color measurement setup:

Color Application Add-on Software (13 FSS 102):

The Color application add-on software has been developed to perform on-line color measurements with a Melles Griot spectrometer system. It can be used for reflective color measurements. This application provides a precise way to perform color measurements using the basic principles and techniques defined by the International Committee on Illumination (CIE). The CIE 1976 L*a*b* color parameters are calculated, as well as other frequently used parameters, like Hue, Chroma and X, Y, Z.

These parameters can be displayed in a CIELAB chart or in a graph versus time. It is 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. By comparing the measured L*a*b* values to the stored database values, color differences (ΔE_Lab, ΔL*, Δa*, or Δb*) can be measured as well.

The color of an object can be expressed by the CIE 1976 (L*a*b*) color space. L* describes the brightness of the color. A positive value of a* describes the redness of the color, a negative a* the greenness. Similarly, yellowness or blueness is expressed by coordinate b*, which is positive for yellow and negative for blue. The L*a*b* values are derived from the CIE tristimulus values X, Y and Z of the sample (object) and the standard illuminant tristimulus values X_n, Y_n and Z_n.

The standard illuminant tristimulus values for X_n, Y_n, and Z_n are constant and depend only on the type of standard illuminant that has been chosen.

The CIE tristimulus values X, Y and Z of the color of an object are obtained by multiplying the relative power P of a standard illuminant, the reflectance R (or the transmittance) of the object, and the 1931 CIE standard observer functions x_λ, y_λ and z_λ (2 degrees angle). The integral of these products over all the wavelengths in the visible spectrum (380 to 780 nm with a 5 nm interval) gives the tristimulus values.

The color chart display has following features:

1. Display in CIELAB chart, the actual sample color as well as the reference color with the corresponding ΔE_Lab, ΔL*, Δa*, or Δb* values are displayed and saved as well.
2. The settings for the LAB chart display can be changed, such as no graphical display of reference and sample color in order to speed up the measurements.
3. New additional option is to select the standard observer angel for 2° or 10°.
4. The reference color can be saved to and loaded from a color database. This color database contains next to all color parameters a product ID and a display of the actual color. The database can be sorted alphabetically or on either value column

The time series display has following features:

1. Display in time series can be done for up to 8 channels.
2. For each channel a color parameter (L*, a*, b*, hue, C, X, Y, Z, ΔE_Lab, ΔL*, Δa*, or Δb*) can be selected, also for each channel a different reference color can be selected, enabling the use as a color sorting.
3. For each channel the time axis can be set to different scale, allowing simultaneous display of long time and short time monitoring of the same parameter.
4. For each channel the actual measured color, as well as the reference color (if in ΔE_Lab, ΔL*, Δa*, or Δb* mode) is displayed.
5. The saved time series data can be loaded again and displayed with extensive zooming and dragging options.