© PCE Instruments
2
2
Working principle
Tristimulus principle: The light source is reflected at the surface of the object and the colour sensor
receives the reflected light. After the digitalisation of the sensor data, the colour coordinates are
calculated and can then be used to determine colour deviations between the standard and the
sample. To do so, use the colour difference formula below.
Colour difference formula:
∆𝐸
∗
= √(∆𝐿
∗
)² − (∆𝑎
∗
)² − (∆𝑏
∗
)²
△
E* = the total colour difference
△
L = L*standard - L*samples
△
L+ = more white
△
L- = more dark
△
a = a*standard - a*samples
△
a+ = more red
△
a-= more green
△
b = b*standard - b*samples
△
b+ = more yellow
△
b- = more blue
Classification of colour difference ranges
△
E
Classification
0
… 0.5
Minor difference
0.5
… 1.0
Small to medium difference, acceptable in some applications
1.0
… 2.0
Medium difference, acceptable in some applications
2.0
… 4.0
Large difference, acceptable for specific applications
4.0
Very large difference, unacceptable
Explanation
: Colour differences are classified differently depending on the industry. Please
familiarise with the industry-specific requirements.
