Fundamentals of Color
Measurement
ISA NorCal TECH May 2
Bill Deutschlander
WorleyParsons 925-313-5628
Spectrum of Light
Microwave
Visible
Radio Wave
10
1
Infrared (IR)
10
-1
10
-2
10
-3
10
-4
10
-5
X-Ray
Ultraviolet
10
-6
10
-7
10
-8
Gamma Ray
10
-9
10
-10
10
-11
10
-12
10
-13
Green
Yellow
Blue
Orange
Indigo
Red
Violet
Near Infrared
3um
2um
Ultraviolet
1um 700nm
400nm
200nm
Spectrum of Color measurement
100
206
400
700
1100
Wavelength
(nm)
385
Ultraviolett
Visible Light
Near Infrared
(UV)
(VIS)
(NIR)
430
Yellow
550
620
670
red
blue
green
= color of liquid
Color Scales and Terms
• APHA - American Public Health Assoc., Hazen
Standard
• ASTM – American Society for Testing and Materials,
Hazen and SayBolt Standards
• EBC – European Brewery Convention; 430 nm, 1 cm
• Hazen – Unit of the Color Standard Scale for
APHA/ASTM. Also know as Pt-Co.
• Saybolt – Color Scale unit for Petroleum Products
based upon visual comparison of Optical Filters
Photometry - Principles
Absorption of light:
I0
IR
Scattering of light:
IS
I0
ID
Absorption - Lambert Beer´s Law I
I = I0 ·exp[-ε ·c ·d]
I0
I
T = I / I0
d
A: Absorbance
T: Transmission
A = – log T = ε ·c · d
ε: Molar decading coefficient
of absorption (l / mol*cm)
c: Concentration of absorbing
substance (mol / l)
d: optical path length (OPL) (cm)
Absorption - Lambert Beer´s Law II
Units of Absorption:
A = – log T = ε ·c · d
A:
Absorbance
E:
Extinction (Europe)
AU: Absorbance Units
CU: Concentration Units
(competitor)
OD: Optical Density
OD = A / OPLcm
Absorption - Lambert Beer´s Law III
5
100
Absorbance
90
4
70
60
% Transmission
3
50
40
2
30
1
20
10
0
0
Concentration
Absorbance (A)
% Transmission
80
Absorption - Lambert Beer´s Law IV
Absorbance
(CU)
A = -log T
0
0,5
1
2
3
4
Transmission
(%)
100
32
10
1
0,1
0,01
Absorption - Different Colors
0,4
Gelb/Yellow
Rot/Red
Blau/Blue
Sig n al ( C U )
0,3
0,2
0,1
0,0
350
400
450
500
550
Wellenlänge / Wavelength (nm)
600
650
700
Color Analysis, e.g. APHA
500 APHA
5 cm cuvette
Absorbance
4
3
2
1
0
380
480
530
580
430
480
530
580
0,5
Absorbance
50 APHA
5 cm cuvette
430
0,4
0,3
0,2
0,1
0,0
380
Wavelength (nm)
Color Analysis
Single Beam
Absorption:
A = ε ·c · d
Dual Beam
Absorption:
Aref
A = Ameas - Aref
Ameas
Color Analysis - Comparison Single
and Dual Beam
Color Intensity
Aref
Ameas
Single Beam Absorption:
Dual Beam Absorption:
• No Turbidity
• Compensation of turbidity
• No Bubbles
• Compensation of bubbles
• Significant color changes
• High sensitivity
• Compensation of lamp aging
Color Analysis - Typical Apps Single
and Dual Beam
Aref
Ameas
• Phase separation:
- Beer / Water
- Wine / Water
- Juice / Water
- Hemoglobin
concentration in blood
• Color dosage
• Quality control / Purity (absence of color)
• Decolorization control
• Color scales: APHA, Hazen, EBC, ASBC, ASTM,
ICUMSA, Lovibond
• Concentration of inks / colorants
• Residual color in waste water
• Metals in solution: Iron, copper, nickel, chromium
• Huminic matter in drinking water
• Chlorophyll in edible oil
• Bleaching of edible oil, sugar syrup...
• Lignin in hydrosulforic acid
• Dissolved water in organics
• Phase separation: organic and aqueous phase
• Chlorine / chlorine dioxide / hypochlorite
Color Analyzer Manufacturers
•
•
•
•
•
Ametek Process Instruments Model 4000
Galvanic Applied Sciences Monitek Monispec AD
Optek Model AF26
Sigrist ColorPlus
Wedgewood Analytical Model AF21, AF22
Ametek Model 4000
GAS Monitek Monispec AD
Optek Control 4000/AF26
Sigrist ColorPlus
Wedgewood Analytical
980/AF21,AF22