Bridgelux introduces new metric for matching LEDs to natural light: Average Spectral Difference

As if we didn’t have enough ways to measure the quality of light, Bridgelux steps up to propose a metric that could be very useful for anyone seeking to create a ‘natural’ lit environment.

Colour metrics based on CRI and, more recently, TM-30 serve us well in determining colour accuracy but, Bridgelux claims, that accuracy omits the most important relationship of all – the one that we have with natural light.

As a consequence of the shift in lighting design parameters towards lighting for health and wellbeing, the role that Natural Light has to play has become much more significant. The WELL Building Standard calls for a closer integration of natural and artificial light. It makes sense, then, that the artificial light should be able to mimic natural light conditions as closely as possible.

We’ve been hearing a lot about ‘flattening the curve’ in another context, but that is a major part of what Bridgelux has achieved with its new ThriveTM range of LED sources. The ‘blue pump’ that has long been the signature of the LED spectral power distribution has been dramatically reduced, enabling the LED’s SPD curve to follow the equivalent curve of the natural light at that colour temperature.

This has the effect of ignoring an enhanced ‘melanopic’ blue component that some manufacturers have promoted. Its Bridgelux’s contention that the enhanced blue is a risk that is not worth taking. If it doesn’t exist in nature, then why provide it as part of an artificial lighting installation? Future generations may thank Bridgelux for their concern for keeping their light ‘natural’.

Rather than enhancing a melanopic blue to unnatural levels, Bridgelux has ensured that the melanopic performance of the ThriveTM LEDs sits within a +/-1.3% variation between the natural light and its LED ‘equivalent’.

Average Spectral Difference

The ASD metric is based on a percentage deviation of 266 spectral segments, each 1nm wide, making up the visible spectrum between 425nm and 690nm. The 266 values are then averaged to produce a single value – the headline ASD value for that source.

There is an equation, of course:

“The ASD value, expressed as a percentage, always compares a test source to a reference source at the same CCT. The reference source used by Bridgelux is the blackbody curve (BBC) for light sources of 4000K and below, and the daylight spectrum (i.e. standard illuminants such as D50, D57 and D65) for light sources of 5000K and above.”

The ThriveTM series is produced across a wide range of CCTs:

2700K – 3000K – 3500K – 4000K – 5000K – 5700K – 6500K.

And, inevitably, the ThriveTM range includes a tunable-white option to further improve the natural-artificial light balance.

Bridgelux has produced a White Paper that discusses Average Spectral Difference in greater detail.

Bridgelux Whitepaper:  Average Spectral Difference, a new method to make objective comparisons of naturalness between light sources 

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