LED Technology


Tunable white LED innovation drives luminaire development for human-centric lighting


By Menno Schakel, technical marketing engineer, Nichia T


unable white solutions play a major role in enabling human-centric lighting (HCL), which is currently one of the primary drivers of lighting innovation. The conventional way to achieve a tunable white solution is to use separate light sources of different colour temperatures. However, new products are emerging which support innovation in HCL luminaire design by having the tunable white solution in a single light-emitting surface (LES). Utilizing one LES, but two separately controllable channels, supports a level of freedom in luminaire design that was previously difficult to achieve with conventional tunable white. Notably, a single LES reduces the need for additional optics or diffusers while still maintaining good colour homogeneity.


A major HCL concept is recreating the natural daily lighting cycle, called circadian lighting. To simulate the daily lighting cycle of the sun means: bright blue light in the morning; neutral daylight at noon; warmer, more relaxing, less bright light in the afternoon and evening; and of course, the absence of light at night.


Tunable lighting products able to create circadian lighting have been available for a few years, using either colour-tunable or tunable white technologies. However, the base whites of the latter can have CRI values which are far greater than that of a colour tunable solution, while the light from a tunable white solution will also have far superior quality. As a final note, the electronics associated with a tunable white solution are less complex.


Breakthrough innovations


In order to assist the improvement of existing


30 November 2021 Components in Electronics


lighting fixture designs and prompt development possibilities for new tunable fixtures, Nichia has developed two new tunable white LEDs: a chip-on-board (COB) style package and a mid-power 3030 package (2-in-1). Both of these solutions offer the benefit of a single LES. Improved colour mixing in a smaller space is the main advantage of a single LES product. The closer the LES of different coloured light sources, the better the colour mixing of the sources. In the new LEDs, the distance between sources is so small that they share the same LES. It is also worth noting that luminaires taking advantage of single LES products can be thinner due to smaller optical distances.


Design options


The small, single LES design of the mid- power package makes it well suited to light-guide designs and, especially, edge-lit solutions. With a single LES it is simpler to couple the light into a light guide and keep a consistent light mixing effect. Luminaire designers also should know that with the mid-power package, it is possible to reduce the canvas or blindfold around the LES of the fixture. Furthermore, fixtures currently designed with 3030 mid-power packages that rely on secondary optics can easily implement the 2-in-1 mid- power package without an expensive redesign. The external dimensions and LES are the same as the current generation of mid-power packages.


Using the COB style package enables the creation of tunable white spot solutions which were previously only possible using direct mountable chip (DMC) or chip-scale


Footprints of 3030 mid-power packages. Standard package (Top), 2-in-1 package (Bottom)


Color tuning locus of the tunable White COB.


package (CSP) technologies. In a spotlight design, a diffuser is highly undesirable as it effectively creates a larger LES, reducing both spot efficiency and effectiveness. For a spot design, the smaller the LES, the more freedom in optical design. Having a small tunable LES available in a ready- to-implement solution, without having to make a peak-design PCB every time, will enable luminaire manufacturers to expand their tunable white portfolio more easily and, hopefully, inspire many new designs. An additional benefit of the tunable COB product is convenience of assembly for the fixture manufacturer: it can be mounted using commercially available COB holders, similar to other COB products.


Colour properties


An ideal tunable white solution would have all of its intermediate colours on the black body locus (the path or ‘locus’ that the colour of an incandescent black body takes in a particular chromaticity space as the black body temperature changes). However, unlike the colour gamut of tunable white solutions, the black body locus is not a straight line. There are very


few points which perfectly match between the two and, the further apart the colour points of the two primary sources, the larger the overall deviations from the black body locus.


A large colour temperature range might seem attractive at first, providing the largest flexibility, but it would lead to larger deviations from the black body locus. A smart selection of primary source colour temperatures based on the application is therefore crucial. With these thoughts in mind – and to guard against the possibility of cross-talk between the closely-located sources – the Nichia COB product has a cool-white colour temperature of 5000 K and a warm-white colour temperature of 2700 K. The potential for cross-talk in the 2-in-1 mid-power product is far less, so it offers up to 6500 K while still maintaining a warm-white of 2700 K.


Ultimately, only through the advent of new LED innovations will it be possible to support luminaire designers as they look to keep pace with rapidly increasing market demand for HCL.


www.nichia.co.jp/en www.cieonline.co.uk


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