New metric quantifies 'naturalness' of light

May 15, 2020 //By Julien Happich
Bridgelux has developed a new metric to enable objective comparisons of light sources to natural light. With the growing market interest in human-centric lighting, the question of "naturalness" of light source spectra is becoming a frequently asked question.

Lighting specifiers, designers, and luminaire manufacturers regularly consider color quality metrics such as CRI and TM-30, as well as individual spectral power distributions (SPDs), when making decisions regarding light source selection. However, until now, there has been no metric that quantifies the naturalness of a light source.

Standard lighting quality metrics such as CRI and TM-30 do not fully address the naturalness question. In order to address this shortcoming, Bridgelux has developed the Average Spectral Difference (ASD) metric, providing an objective measurement of how closely a light source matches natural light over the visible spectrum, averaging the differences of the spectral peaks and valleys between a light source and a standardized natural light source of the same color correlated temperature (CCT).

The ASD value is a quantitative metric of the SPD differences. Unlike CRI and TM-30, where higher values indicate higher quality light, ASD represents the difference in spectra compared to natural light, therefore the lower the ASD value, the closer the match to natural light.

The Bridgelux Thrive LED light source family has been engineered to provide the closest match to natural light available in the market.  The ASD values for standard light sources are much larger compared to Thrive, including that of the 98 CRI light source. While TM-30 and CRI are important color quality metrics, having high values does not necessarily correspond to high naturalness of the light source, whereas having very low ASD values always corresponds to high naturalness.

"The market is evolving to human-centric lighting," comments Brian Cumpston, VP Solutions Development of Bridgelux. "While there are several approaches to developing human-centric lighting solutions, delivering the closest match to natural light is of great interest to our customers. Thrive has been developed to address this demand, and the new ASD metric developed by Bridgelux provides an objective and quantitative way to compare light sources and determine how closely they match the spectra of natural light.  We

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