What is CIE L*a*b*? And the difference between Agtron and CIE L*a*b*?
CIE L*a*b* is a colour system created in 1976 by the International Commission on Illumination to describe colour the way humans actually see it. It uses only visible light (390-720 nm) and describes colour using three dimensions:
L* for lightness, a* for red to green, and b* for yellow to blue.
What is CIE L*a*b* actually measuring?
CIE L*a*b* works by applying visible light on the coffee sample and measuring how it is reflected across the spectrum. The reflected light is processed into L*, a*, and b* values. These values describe the coffee’s appearance as humans perceive it. By comparing them to reference beans with known roast levels, roasters can classify light/medium/dark roasts, or calculate a roast index based on visual perception.
Why CIE L*a*b* is getting attention?
SCA is bringing out CIE L*a*b* to provide a direct, standardised way to describe what humans actually see.
Agtron works differently - as it measures near-infrared light, which we cannot see, and converts it into a number that reflects roasting-related chemical and structural changes. Agtron does not directly measure visual colour, though the number correlates with roast level.
Below is the summary of brands/models of commercial instruments, demonstrating what technology that they use and how they measure/obtain Agtron and CIE L*a*b*.
|
Brand / Model |
Sensor technology |
Spectral range (nm) |
Colorimetry logic (L*a*b*) |
QC metric (ΔE - colour contrast) |
|
Konica Minolta CR-400 /CM-700d |
Spectrophotometer (Xenon Flash) |
360-740 nm |
Native CIELAB. Full integration of XYZ via D65/2° or 10°. |
Industry gold standard. High-precision ΔEab and ΔE00. |
|
DiFluid Omni |
Multi-Spectral Array + 2D NIR Imaging |
400-1100 nm |
Calculates L*a*b* from visible bands; converts L* to Agtron. |
Calculates ΔE to compare batches against a saved target. |
|
LeBrew RoastSee C1 |
VIS + NIR Fusion (Photo-diode Array) |
400-1100 nm |
Derived. Uses visible bands for colour correction and L* mapping. |
Supported. Primarily used for batch-to-batch consistency tracking. |
|
Agtron E20CP |
NIR Photometer (Solid State) |
~850-880 nm |
Does not capture visible wavelengths. Cannot generate L*a*b*. |
N/A. Relies solely on 1D Agtron unit variance. |
|
Lighttells CM-100 Plus |
NIR Photometer |
800-1100 nm |
Blind to the visible spectrum (Rλ at 400-700nm). |
N/A. Only measures NIR reflectance intensity. |
|
ColorTrack |
Laser Reflectance |
~780-850 nm |
Uses high-speed laser to estimate darkness/caramelisation. |
Limited. Focuses on laser reflectance deviation. |
Visible range: 380-780 nm (this range can be seen in human eyes).
NIR range: normally starts from 700/780-2500 nm, but commercial NIR photometer used in coffee beans mostly ranges from 780-1100 nm.
To make it easier to understand, please see attached picture to see how they work:
