Cyanosis Observation Index of a Light Source - A Method for Determination

The following text refers to AS/NZS 1680.2.5 Interior Lighting Part 2.5: Hospital and Medical Tasks. One should make sure that this version is current at the time of reading and confirm whether or not national deviations exist.


Clause 7.2 of this standard mentions the properties demanded of the light source used in region where visual conditions suitable to the detection of cyanosis should be provided.

  1. The correlated color temperature (CCT) of the source should be from 3300 to 5300 K
  2. The cyanosis observation index should not exceed 3.3

The means of determining the cyanosis observation index is provided in appendix G.


The principle is derived from the magnitude of the calculated change in color appearance of oxygen-reduced (cyanosed blood at 50% oxygen saturation) and of fully oxygenated blood (100% oxygen saturation) when illuminated by the source under consideration compared with a 4000 K reference illuminant.

Data is given for the spectral reflectance of cyanosed and oxygenated blood, to be multiplied by the spectral distribution of the source under consideration - throughout the spectral range 380-780 nm, in steps of 5 nm.

Calculating the resulting color in CIE L*a*b* space and comparing with a 4000 K reference illuminant gives a value of cyanosis observation index (COI). The lower the value of COI, the smaller the shift in color appearance results under illumination by the source in question.

This information has been sourced, reviewed and adapted from materials provided by Bentham Instruments Limited.

For more information on this source, please visit Bentham Instruments Limited.

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