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Colour rendering index (CRI) is a common metric used in visible lighting that indicates the quality of a light source. It refers to the light source’s ability to show the actual colours of objects in comparison with natural sunlight. A high CRI value will mean clear crisp colours.
So, does CRI matter when considering horticultural lighting applications? The short answer is no, no CRI is not important for plant growth or health.
A grow light that advertises a high CRI value, just means that the light has a better capability to accurately reveal the colours of the plants it is illuminating, as they would appear under natural sunlight.
CRI is a human metric. It measures how light and colour are perceived specifically by the human eye. Plants perceive light very differently to humans; human sight has a better perception of green and yellow light than blue and red light, which differs from a plant’s perception of light. Therefore, in horticulture, CRI is less relevant.
So, CRI is not important for plant growth, so why is it sometimes considered in horticultural applications? Well, as mentioned it indicates how good visibility is for humans. Therefore, many growers look to CRI ratings to ensure that growing environments, particularly indoor applications, have good visibility and conditions for workers. With high CRI grow lights, it is easier for growers and workers to distinguish a plant’s true colour and condition.
So overall, it is more important in horticultural lighting to focus on metrics other than CRI such as wavelength, intensity, and duration of LED exposure. These factors, when utilised effectively will help stimulate photosynthesis processes within plants and thus influence growth speed and/or quantity. Learn more about other metrics in horticulture here. Or learn more about CRI and why it can be useful here.
