Cyanosis Observation Index (COI) Explained

The Cyanosis Observation Index (COI) is a metric that is used to evaluate the quality of white light sources for their ability to render the color of blood in human tissue accurately. Specifically, it measures the ability of a light source to reveal cyanosis, a medical condition in which the skin and mucous membranes appear blue due to a lack of oxygen in the blood.

In the context of lighting, COI is an important consideration for healthcare facilities, such as hospitals and clinics, where accurate color rendering is essential for proper diagnosis and treatment of patients. COI is measured on a scale of 0-100, with lower values indicating better color rendering performance.

To calculate the COI value, a color rendering index (CRI) test is performed using a standard set of color samples, including a "cyanotic sample" that mimics the color of human tissue under cyanotic conditions. The test measures the ability of the light source to accurately reproduce the color of each sample compared to a reference light source, such as a blackbody radiator.

In general, light sources with higher COI values are considered to be better suited for healthcare environments, as they can help medical professionals to make more accurate diagnoses and provide better treatment for patients. However, it is important to note that COI is just one of several metrics used to evaluate the quality of white light sources, and it should be considered in conjunction with other metrics, such as CRI, color temperature, and illuminance levels, when selecting lighting products for healthcare applications.

The correct standard for COI observation is AS/NZS 1680.2.5:1997 Interior lighting Part 2.5: Hospital and medical tasks. a COI value of 3.3 or less is required by this standard for correct cyanosis observation.