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FEATURE OPTOELECTRONICS


A light bulb moment The science and technology of human-centric


lighting explained Words by Dr Ulf Meiners, managing director, Nichia L


ED lighting has long offered energy- efficient lighting and luminaires,


but some questions have remained over light quality, particularly colour rendering and glare. Thankfully, LEDs save on energy and lifetime cost, with quality maintained. In fact, LEDs offer the potential to redefine quality of light – going far beyond just clarity, colour and visual comfort, to take into account how light impacts health and behaviour. The result is ‘circadian rhythm’ lighting, which adjusts light throughout the day to stay in tune with the body’s clock. This is now a big growth area for LED lighting. And yet, trade-offs still remain. It is a challenging balancing act for lighting manufacturers to develop solutions that ensure human-centric lighting solutions hit a ‘sweet spot’ of delivering a maximum level of vitality to occupants in an illuminated space, at an ideal level of luminous efficacy. But, it is necessary to understand that it is not the actual appearance of light that affects the human circadian rhythm – it is the exact spectral composition and optimisation. Research has highlighted that eye accommodation response is faster with a broad spectrum, while human eyes do not fatigue as a result of a broad-bandwidth light source. It is well documented that the sensitivity curve for intrinsic photosensitive retinal ganglion cells (ipRGCs) hits its intensity peak in the cyan region. To explain further, ipRGCs in human eyes (neurons that primarily project to non-visual areas of the brain) react to wavelengths of 470 to 520nm, which are chiefly cyan or of a greenish- blue light. Thus, to stimulate humans, a light source must offer sufficient cyan. Although white LEDs


typically comprise a blue light source topped with a layer of phosphor, this type of light source does not usually deliver sufficient cyan in its spectrum, as this can compromise luminous efficacy. As a result, standard LEDs have little or no impact at all on the human circadian rhythm.


14 MARCH 2020 | ELECTRONICS


Despite the fact that LEDs offering a colour rendering index (CRI) of 80 have been adopted across the industry, to engender more market growth, manufacturers must concentrate on added value, with a higher-CRI LED performing as a technical differentiator. A handful of LED manufacturers are closing the performance gap between CRI ≥80 and higher CRI, with some already achieving a performance gap of only 20lm/W between an LED offering CRI ≥80 and an LED with CRI ≥90. This efficacy gap should not be neglected when designing the latest luminaires and, as previously stated, the role of cyan is key to the improvement of spectral distribution. Take the discovery of the International Commission on Illumination (CIE) that, with advancing age, transmission of the eye’s crystalline lens between 400 and 500nm reduces, and changes to a yellowish colour. Consequently, emphasising the cyan component in the spectral bandwidth provides clearer vision for middle-aged and older adults.


Based on new research, Vitasolis, a proprietary lighting technology from Nichia, looks to capitalise on the benefits of LEDs, but also the principles of human-centric lighting, using strontium aluminate that is


Spectral absorptance of human retail photoreceptors


An example of the Vitasolis spectrum


LEDs are no longer a simple solution to visibility problems - they play a key role in the Internet of Things and smart systems


activated with europium (SAE), a unique phosphor composition that is combined with a blue LED featuring marginally longer peak wavelength. Despite the enhanced cyan energy, spectral control and phosphor technologies combine to enable a natural white colour, allowing the optimum characteristics of light to have a positive impact on circadian rhythm without losing efficacy from a typical CRI ≥80 LED. For design engineers developing luminaires, the solution could not be simpler, being adopted easily and quickly in existing designs as a replacement for other LEDs, without any changes in power, driver compatibility, beam shape or safety testing. There is no need to adapt or redesign fixtures – simply swap out the


standard LED. So, energy savings can be achieved by a light source that is


truly human-centric. Additionally, such technologies can be integrated into smart, tuneable fixtures and IoT systems to enable customisation of localised lighting in real time, with users able to control local light level intensity and colour temperatures, among other characteristics.


Nichia www.nichia.com / ELECTRONICS


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