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Colour measurement
Spectrophotometry: Colour measurement according to DIN 5033-4:
Functional principle:
A spectrophotometer is a photometer that can measure intensity as a function of the light source wavelength. Important features of spectrophotometers are spectral bandwidth and linear range of absorption or reflectance measurement.
It measures the reflectivity of the sample after calibration on black and white standard, independent of the light source of the photometer.
On the basis of these values a reflectance curve is set up for the measured colour. This curve is like a finger print in terms of colour.
A photoelement determines the amount of light reflected from the reference and test samples and evaluates the ratio. By multiplying the metered values of each beam by the standard values, it is possible to calculate the corresponding colour values.
Often, the CIELAB colour scale or the CIE system are used.
There are two major classes of devices: single beam and double beam. A double beam spectrophotometer compares the light intensity between two light paths, one path containing a reference sample and the other the test sample.
The most precise measuring devices known today is the double beam photometer.
(Source: Wikipedia, German version)