Application Setup: Reflectance

Overview

Colour measurement involves determining the reflectance spectrum of a sample with reference to a standard illuminant (that is, a light source with a defined spectral power distribution). The amount of light energy the sample reflects is manipulated and reduced to tristimulus values X, Y and Z. These values correspond to the physiological response of the three types of colour receptors in the human eye (red, green and blue). X, Y and Z values are transformed into colour space values such as CIELAB (L*, a* and b*).

Spectrometer

A USB4000 with a 25µm Slit and Grating #2 (350-1000nm) works well for colour analysis. For those using an integrating sphere as the sampling optic, we recommend an L4 Detector Collection Lens to compensate for sphere losees and improve measurement sensitivity.

Sampling Optics

When taking reflected colour measurements, your data depends on the chosen sampling geometry. Industry-specific conventions may determine your preferred sampling geometry, otherwise choose that which best matches the intended application of the material under test. The R400-7-VIS-NIR Reflection Probe provides illumination and detection from the same direction. If you use the probe at 45°, it measures directional diffuse reflectance. If you use the probe at a 90°, it measures specular (i.e. mirror-like) reflectance. The distance from the probe to the surface determines the sample size. An alternative is the ISP-REF Integrating Sphere, which provides hemispherical illumination for measuring the total, diffuse and specular reflectance of scattering materials.

Measurements

Sample reflectance is measured with reference to a reflectance standard such as the WS-1-SL Diffuse Reflectance Standard. SpectraSuite Spectroscopy Operating Software calculates a variety of colour space values from the reflectance spectra.

Ordering Information

All prices are ex works Pro-Lite and exclude VAT. Prices correct at 24/10/07 but are subject to change without notice