Bin Ten

(Pun intended – with apologies to the goddess Benzaiten and Ben 10)

 

Despite the billions of research dollars poured into LED research, LEDs produced in a batch

still vary considerably in light intensity, colour temperature, and voltage. Hence, the introduction of binning – sorting LEDs after production according to lumens, voltage, and colour temperature – so the final luminaires produced will have more uniformity in terms of these criteria. However, even with binning, the LED colour temperature perceived by the human eye still creates inconsistencies. This is because the colour temperature we see in LEDs are also influenced by the angle by which we view the light source. Since 1931, light sources have been rated for the standard observer colour space of 2 degrees (CIE 1931 2°). This meant that the field of view for rating colour space was limited to 2° (a diameter of 17mm at a distance of half a meter). Any angle greater than 2 degrees and the colour temperatures we perceive tend to be different even if light sources have the same colour location (coordinates). This difference in colour temperature perception is more pronounced for LED lights because, even if the LEDs are binned for the same colour location, the eye still perceives the minute differences in the blue colour spectra produced by individual LEDs. This leads to LED lamps binned for the same colour location being perceived as differently bluish, yellowish, cool or warm even if, in theory, they should all be perceived as the same. This inconsistency can be reduced by increasing the angle for the colour space by which LED lights are rated and binned.

Enter Ten°

The 1931 observer colour space standard was made during a time when it was thought the red, blue, and green receptor cones in the human eye were uniformly distributed. Now we know better and some lighting manufactures have responded for some time by rating and binning lighting applications at a field of view of 10° (a diameter of 90mm at a distance of half a meter). This rating for colour perception is closer to how our eyes are constructed to perceive colours. With the new scheme, even with the greater angle of viewing, light sources rated for colour matching in ten degrees will have less perceived colour variations than those binned for two degrees. But this scheme is not yet widely adopted.


There have been two attempts by CIE to change the standard observer colour space for the lighting industry from 2° to 10° – one in 1964 (52 years ago) and another one last year (2015). Called the CIE 2015 10° u′ v′ colour space, this latest attempt to bring the standards up to the same level with current knowledge in colour perception is gaining recognition.


At least one famous LED manufacturer, Osram Opto Semiconductors, is now using a ten-degree based white binning method, dubbed ‘Ten°’ (from the CIE 2015 10° u′ v′ color space recommendation) on its new Soleriq LEDs. Since binning for ten degrees complies and is compatible with current standards and white groupings (binnings), using it is a win-win situation. Expect more LED products from more companies to be binned for 10° in the near future.

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