Opinion: while daylight is a ubiquitous resource that we often take for granted, it has complex long term impacts on our well-being 

Daylight is very good for our health, it saves energy that would otherwise be used for electric lighting and it is aesthetically pleasing. It is a ubiquitous resource to which, surprisingly, we often do not give a second thought.

Being in daylight is when we have our best visual performance. It is well known that vitamin D is produced by exposure of skin to the ultraviolet light in the solar spectrum. It is perhaps less appreciated that it produces the neurotransmitter serotonin which can improve one’s mood. Thus maximising the daylight in buildings is not only intrinsically beneficial, but also contributes to the creation of productive working environments.

Daylight is also a powerful cue to the maintenance of the circadian pacemaker within all of us that follows the cycle of night and day. Being crucial to the healthy regulation of our hormonal rhythms, it has a huge impact on our cognitive performance. More generally, the fact that the ultraviolet part of daylight kills germs means that it is also important for hygiene.

"We are intimately reliant on and predisposed to being in daylight"

Daylight also has much broader and more complex longer term impacts on our well-being that are only now beginning to be understood. For example, the lower annual cumulative solar exposure experienced by people living at higher latitudes appears to be associated with negative health effects, such as a significant association with earlier onset of multiple sclerosis. 

Another example is the role of daylight in enabling our eyes to develop properly. In some wealthier, hotter countries, many children appear to receive insufficient exposure to daylight because most time is spent in interior artificially-lit environments because of their air conditioning. This appears to be contributing to epidemic levels of myopia in many countries; for example up to one-fifth of children completing secondary schools in Taiwan, Singapore and Hong Kong often need glasses or contact lenses to correct severe myopia.

We are therefore intimately reliant on, and thus predisposed to being in, daylight. During the day, we like to be in day-lit living and working interior environments. Bringing daylight into buildings, even with overcast skies, does usually provide sufficient illumination for the majority of activities during most of the day and has thus been a critical part of building design. From classical Roman to modernist architecture, windows and verandas have faced to the sun and atria and lightwells have been designed to allow daylight into deeper plan buildings.

The fact that the ultraviolet part of daylight kills germs means that it is also important for hygiene

As well as configuring buildings properly by elongating buildings along an east–west axis, good daylighting techniques include allowing daylight to enter high into rooms, admitting daylight from multiple sides of a space, mitigating direct sunlight from producing glare and using light coloured interior surfaces. Including features that allow daylight deeper into rooms is usually combined with controls that then turn-off artificial lighting to reduce electricity use. It also requires care in the location of activities: for example highly visual tasks should be done near a naturally-lit building perimeter, but computer screens should be perpendicular to windows.

Daylight is often accompanied by solar heat gains through southerly-facing windows that reduce the auxiliary heating energy used to maintain comfort when outdoor conditions are cold. Even in hot climates, solar heat gain is useful as it can drive buoyantly-driven air flows that provide cooling by drawing air in from shaded areas. Technological systems collect the sun’s energy to heat fluids or produce electricity. 

In solar thermal collectors, a fluid flowing through usually a metal absorber typically transfers solar heat for applications from domestic hot water up to electrical power generation. The solar energy, of which daylight is a part, can also be converted directly to electricity in solar photovoltaic modules, using particular combinations of materials that absorb solar radiation to generate an electrical current.

"More emphasis on a holistic understanding of the many unexpected aspects of daylight will better allow us to optimise how we best use it" Photo: Darren Joyce

Much of this may seem obvious. But with the advent of electric lighting, air-conditioning, lifts and escalators, buildings not only became larger and taller, but also often have deeper plans with limited penetration of daylight. As a result, many people now spend much of their day in artificially lit spaces, from offices to shopping malls. This has consequences as more people receive insufficient vitamin D from their diet and limited exposure to sunlight. Eighty years after it was thought to have been eliminated, rickets, a disease caused by sunlight deprivation, is seeing a resurgence.

But optimising our exposure to daylight is not simple and requires awareness of many counteracting factors. Whle too little daylight for too short a time produces insufficient vitamin D, too much exposure for too long can induce freckling, sunburn and skin cancer in those susceptible. In buildings, providing adequate daylight is generally good, but creating conditions that lead to glare must be avoided.

Properly supporting the stimulus that maintains our daylight-driven circadian rhythms is also far from trivial. It requires a complex combination of light intensity, duration and timing of exposure to daylight, the amount of blue wavelengths in the received spectrum and that daylight’s spatial distribution. More emphasis on a holistic understanding of the many unexpected aspects of daylight will better allow us to optimise how we best use it.

The views expressed here are those of the author and do not represent or reflect the views of RTÉ