With a growing interest in human-centric light and with tandard lighting quality metrics such as CRI and TM-30 do fully address the naturalness question, the e Average Spectral Difference (ASD) metric has been developed by Bridgelux to address this in available light quality metrics.
Lighting specifiers, designers, and luminaire manufacturers regularly consider colour 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.
ASD looks to provide 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 standardised natural light source of the same 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 colour 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," said 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 hope this new metric will be broadly adopted in the lighting industry to provide new insight into naturalness beyond CRI and TM-30."
Bridgelux has authored a white paper further explaining the background behind the ASD metric which is now available for download from the Bridgelux web site.
