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December 21, 2021

Optical Brightening Agents (OBAs)

Synonyms: Optical Brightening Agents (OBAs), Optical Whiteners, Fluorescent Brightening Agents (FBAs), Fluorescent Brighteners, Fluorescent Optical Brighteners, Fluorescent Whitening Agents (FWAs), Fluorescent White Dyes, and Organic Fluorescent Dyes

What are OBAs?

 

Optical Brightening Agents (OBAs) are chemical compounds that give a whitening effect to the substrate/fabric. They do this by absorbing light in the ultraviolet (UV) and violet regions and re-emit the light in the blue region. This phenomenon is called fluorescence and is the reason for many color issues 

This blue light emission reduces the yellow color of the substrate and gives a brightened look. But this impression is caused by a non-visible component of the light (UV). Unlike bleaching, it doesn’t leave a yellowish tinge and gives a much pleasing whiter-than-white appearance. 

The effect of the visual appearance is dependent on the SPD curve of the illumination, if the illumination has UV components, it will excite and enhance the blue emission; the illumination has no UV, then the effect of the blue emission will be minimal.

Due to their properties, OBAs are widely used in industries such as:

  • Paper
  • Textiles
  • Plastics
  • Cosmetics

 

How to detect and quantify OBAs?

ChromaChecker Substrate Inspector calculates two metrics that are very useful to quantify OBAs. First is OBA Index, which calculates the difference in the measurement between M1 and M2 (which requires a measurement device to measure these two modes). Secondly, CC Capture drives multiple instruments capable of measuring in both M1 and M2 measurement conditions which are required to calculate the OBA Index.

These Instruments are capable to measure OBAs Index or FI  that can be used with CC Capture Substrate Inspector:

  • X-Rite i1Pro 2
  • X-Rite i1Pro 3
  • X-Rite i1iO 2
  • X-Rite i1iO 3
  • X-Rite eXact
  • Techkon SpectroDens
  • NIX Spectro 2 (new model with M2)
  • Konica Minolta Myiro-1 (soon)

Steps to measure OBA's

  • Launch CC Capture connected to your Instrument, log-in, go to Substrate Inspector
  • Calibrate Instrument
  • Place your sample on BW SI Backer (not mandatory for opaque objects)
  • Click on "+ Add New Substrate", Name it, and select at least one  application
  • Click on "+ Add new measurement", then measure with averaging - relocate instrument every measurement to get more accurate data.



    OBA index is 8.8 in this case

 

Important Note

Please notice that the same sample measured with a different instruments reports vastly different Fluorescence Index (FI) or OBAs Index.

This is due to significant variations in the device illuminants and other variables. Many technical solutions have been focused on increasing the speed between measurements. Design and methodological simplifications mean that much of the measurement data is the result of processing by algorithms and does not always come directly from actual measurements.The part of the instrument that illuminates light to reflect off sample and pick up the reflected (color) result (especially in the UV range), deviate from the defined references they are supposed to follow. Manufacturers have introduced "data optimization" solutions that actually manipulate the data to enhance speed but do not follow the defined illuminant reference within the M1 specification. As different instrument manufacturers implemented different "short cuts” the end results are significantly different from one another as the table above proves.

 

Instrument Comparison Experiment 

In this experiment, the T42* substrate that contains OBAs is measured with a number of different Instruments. The following table compares the differences between these measurement devices related to measuring samples with OBAs:

 Instrument

OBA

Index

Fluorescence

Index

M1-M2 Spectral ∆ 

 @ 430 nm

M1-M2

 ∆E00 

i1 Pro 3  8.8 9.5 0.24@ 430 nm 8.71
i1 Pro 2  7.2 7.4 0.21@ 430 nm 7.24
eXact M1 Part 2 export on 5.8 5.8 0.16 @ 430 nm 5.72
eXact M1 Part 2 export off 6.2 5.9 0.15 @ 430 nm 6.08
Techkon SpectroDens 7.9 7.4 0.16 @ 440 nmn 7.25
NIX Spectro 2  soon      

 

Fast visual comparison of spectral curves explains why numbers are very different.

 Instrument Reflective Spectrum (M1, M0, M2)
i1 Pro 3 
i1 Pro 2 
eXact M1 Part 2 export on
eXact M1 Part 2 export off 
Techkon SpectroDens
NIX Spectro 2  soon

 

 Instrument Fluorescent Effect (M1-M2)
i1 Pro 3 
i1 Pro 2   
eXact M1 Part 2 export on
eXact M1 Part 2 export off 
Techkon SpectroDens v4
NIX Spectro 2  soon

 

Some of the differences between instruments are due to measurement devices measuring different spectral ranges, but the most critical difference is due to differences in their Light source (illuminants) and monochromator.

 Instrument Light
Source
Monochromator
Detector
Comments
i1 Pro 3  Full-Spectrum LED  diffraction grating
128-pixel diode  array
 
i1 Pro 2  Gas-filled tungsten (illuminant A)
and UV LED

diffraction grating
128-pixel diode  array

 
eXact Gas-filled tungsten (illuminant A)
and UV LED
DRS spectral engine
Two different calibrations for simultaneous M-condition measurement. M1 (part 1), M1 (part 2)  
Techkon SpectroDens v4  Full-Spectrum LED diffraction grating  
NIX Spectro 2  Full-Spectrum LED diffraction grating  

 Additionally. eXact has two modes (M1 Part 2 Export on or off)

 

 

 

 

 

 

 

 

 

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