Method for determination of Cyanosis Observation Index of a Light Source
26 November 2018
The following text refers to AS/NZS 1680.2.5 Interior Lighting Part 2.5: Hospital and Medical Tasks. One should ensure that this version is current at the time of reading and verify whether or not national deviations exist.
Clause 7.2 of this standard specifies the properties required of a light source used in areas where visual conditions appropriate to the detection of cyanosis should be provided.
a. The correlated colour temperature (CCT) of the source should be between 3300 and 5300K
b. The cyanosis observation index should not be greater than 3.3
In appendix G is provided the means of determining the cyanosis observation index.
The principle is based on the magnitude of the calculated change in colour appearance of fully oxygenated blood (100% oxygen saturation) and of oxygen-reduced (cyanosed blood at 50% oxygen saturation) when illuminated by the source in question compared with a 4000K reference illuminant.
Data is provided for the spectral reflectance of oxygenated and cyanosed blood, to be multiplied by the spectral distribution of the source in consideration - over the spectral range 380-780nm, in steps of 5nm.
Calculations of the resulting colour in CIE L*a*b* space and comparison with a 4000K reference illuminant leads to a value of cyanosis observation index (COI). The lower the value of COI, the smaller the shift in colour appearance results under illumination by the source under consideration.