Why is an EU daylight standard needed?

Global climate change and global conservation movements, in recent years, have brought carbon emissions and energy efficiency to the forefront of many governments’ policies. This has seen an aggressive push to improve energy performance across Europe. Better use of daylight in buildings could play a major part in achieving these objectives.

Bringing standards up to date

Due to a previous lack of regulatory imperative, much needed improvements in daylight standards have been extremely slow in coming. Many of the current assessment methods used by regulators, such as Daylight Factor, were developed several decades ago when calculation tools, and our understanding of daylight, were far more rudimentary than today.

This is despite the subsequent development of several more comprehensive dynamic modelling tools – including Climate-Based Daylight Modelling, developed more than a decade ago.

Four criteria to measure daylight

A new standard is being developed for daylight in buildings across Europe (EN 17037). This new standard proposed to establish a minimum recommendation for four daylight criteria – average daylight levels, protection against glare, exposure to direct sunlight, and possibilities for viewing out.

These criteria are not of equal importance and may even work in opposition to each other, which is why it is important to ensure they are correctly balanced.

Four criteria to measure daylight

With the latest draft published in May 2018, this standard is the first step towards a unified approach to daylighting of buildings in European countries. It is clearer, less prone to loopholes and more rigorous than existing sustainable building certifications such as BREEAM, HQE and LEED.

A new look at an old proposal

This new standard is actually based on a methodology originally proposed in a 1970 report by the International Commission on Illumination, entitled “Daylight”. After being overlooked for several decades, it is finally making an impact.

This report proposed a target daylight factor that could provide an average of 300 lux within a given space, a value supported by a number of later studies. The report then required a design to achieve this target daylight factor across the working plane above a specified percentage of a space’s floor area for a minimum of half of the daylight hours in one year.

Daylight is never the same

Ideally, a daylight standard should account for the changing levels of light that occur over the course of a day and over the seasons, to ensure consistent and comfortable lighting is maintained throughout a space. In reality, daylight conditions are extremely difficult to predict, which is why this new EU standard aims to ensure the context of a space is taken into account when assessing adequate levels of daylight.

Unfortunately, the new EU standard is still fairly limited. The daylight criteria currently utilised are expressed in absolute values to provide the same visual comfort across Europe. However, to achieve real fixed daylight targets, the entire building and its surroundings, and the different building types, locations and climates found around Europe will also need to be factored in.

Implementing the daylight standard

Even though a daylight standard can only really evaluate a space based on numerical criteria, the purpose of the space and the distribution of daylight can never be overlooked. For example, while uniform illumination may be ideal for a large workspace, variation of light and dark spaces may be more appropriate in a private living space.

It is up to architects to use their experience, or that of a daylighting designer, as well as comprehensive design tools to ensure their design approach meets both the daylight standard and is suitable for the eventual purpose of the space.

Highlighting the importance of daylight

This new EU daylight standard has the potential to generate renewed focus on the importance of daylight – and the need for better daylight design – among architects, government policymakers and building owners. The importance of daylight has been underestimated for too long, and these new regulatory controls will serve to address these issues.

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