The key role played by switchable glass in implementing the new daylight standard
Based on the latest research findings, this standard sets out recommendations for daylight provision in interior spaces and also addresses the issues of view out, exposure to sunlight and protection against glare. With their smart control systems, switchable solar control glass products such as Halio make a vital contribution to modern daylight planning.
Around a century ago, light started becoming a focal point in architecture. At that time, efforts were under way to tackle cramped urban living conditions and ensure ”light, air and sun for all”. Light, and daylight in particular, was considered primarily one part of a healthy living environment. The health aspect was limited to the biological impact of non-visible sunlight such as infrared and ultraviolet (UV) light. It was recognised that UV light killed germs and that abundant sunlight alleviated skin conditions, vitamin D deficiency and rickets.
In the early days of research into light, the idea was to cheat nature by using artificial light. In fact, that is what led to the emergence of the 24-hour factory. The theory was that humans, chickens, plants and other living creatures just needed the right light – i.e. electric light – to increase their productivity. Modern-day light researchers take a more nuanced view based on recent findings regarding the non-visual effects of light.
Around the turn of the century, researchers discovered a receptor in the eye that detects the light-sensitive molecule melanopsin and has a direct impact on our circadian rhythm, our body’s internal clock, thereby keeping bodily functions such as our immune system and metabolism working properly.
Light affects us in many ways, depending on criteria such as the time and length of exposure, horizontal and vertical illuminance, and the light spectrum. It is known that the high level of blue in morning light curbs the release of melatonin (the ‘sleep hormone’) and boosts the release of serotonin, causing us to wake up. In the evening, exposure to cold white light mimicking daylight delays the production of melatonin, making it harder for us to fall asleep. The more time we spend indoors, the more disconnected we become from our natural body clock. It is now known that a disrupted body clock increases the risk of certain diseases.
Most of the properties of natural light can be reproduced with artificial light. Why, then, do we respond more favourably to the intensity of natural light and changes in this type of light? And why does it have such a major influence on our moods and help us achieve a more holistic perception and understanding of our surroundings? Given the complex mechanisms at play as far as light is concerned, we are still a long way from arriving at a set of general specifications for dynamic lighting design in buildings.
However, some pointers have become apparent. Canazei et al., for example, in their June 2019 publication Human Centric Lighting (HCL): eine Zwischenbilanz (Human Centric Lighting (HCL): an interim assessment), recommend ensuring the highest possible level of daylight provision and supplementing cold-white artificial light with high levels of vertical illuminance during the day and, in the evening, reducing the percentage of vertical light and ensuring that visual tasks are lit as and when required. The authors also note that daylight raises users‘ tolerance threshold for higher light intensities, meaning that they notice visual discomfort significantly later. Furthermore, they report that users rate the quality of light provided by daylight more highly than any artificial light source and also that daylight is the most efficient light source at increasing vertical brightness levels.
The greater the influx of natural light, the harder it is to strike a balance between daylight provision, exposure to sunlight and heat radiation.
For these three criteria in particular, EN 17037 provides designers and developers with basic target values for daylighting interiors. In this connection, the standard distinguishes between three levels: minimum, medium and high. It introduces the concept of daylight provision, which for the first time assesses daylight quality over a whole year and factors in local meteorological data. The individual levels are reached when 50% of the space achieves the respective target illuminance for 50% of daylight hours and when at least 95% of the space achieves the minimum target illuminance for 50% of daylight hours.
The standard also defines three recommendation levels, minimum, medium and high, for view out of the space, exposure to sunlight and protection from glare. One innovation is that for the visual connection with the world outside, users’ location in the space is taken as a reference point and the assessment includes whether the sky and the ground are visible. For exposure to sunlight, the duration of such exposure (minimum recommendations from 1.5 to 4 hours) is calculated on a given key date when a particular minimum, geographically different solar elevation angle is exceeded.
The reference points are at window level. Lastly, for glare protection, EN 17037 recommends a Daylight Glare Probability (DGP) metric, indicating the likelihood that somebody will be dazzled by light. Parameters such as vertical illuminance at eye level, luminance, and solid angle and position index of the glare source are factored into the DGP simulation. Aside from conventional shading systems, the only suitable means of solar and glare protection recommended is low-transmission or electrochromic glazing, which allows only very low light transmission in its dimmed state.
Although EN 17037 sets very low minimum requirements for daylight provision – even on an overcast winter’s day, the illuminance reaching our eyes outdoors is still 3,000 lx – it does reflect the growing importance attached to daylight planning.
In its clear state, Halio glass has a light transmission value of 65%. With a colour rendering index of 97% in its clear state it is a completely neutral colour, and no unnatural blue cast, grid patterns or erratic gradients occur even as the glass tints to shades of grey. Halio glass can tint to a minimum light transmission value of 2% in under three minutes. This is much faster than any other system currently on the market. Depending on the glass structure, Halio glass achieves Ug values of up to 0.6 W/(m²K).
Halio is therefore recommended for all sustainable building projects, whether Passive House, Minergie, BREEAM or LEED-certified. Halio dynamic glass is the future of the facade. Modern facades self-adjust automatically, incorporate dynamic solar protection and provide perfect thermal insulation and natural light, all combined with a sleek design. With its smooth and precise glass tinting technology, Halio makes facades and smart buildings even smarter and more efficient.
This highly automated system is controlled by the Halio Cloud, which communicates with all common building automation systems and can be operated via apps, voice commands or decentralised control panels.
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