What is Visual Comfort?

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What is Visual Comfort

Light has always been a source of warmth, health and happiness for mankind.

We need light to be able to perform most tasks.

So, from very early on, we have tried to replicate natural light.

But early forms of artificial lighting were expensive and not very good!

Therefore, the hours of daily activity closely followed the hours of natural daylight.

Advances in the late 19th century freed us from total daylight dependence…

and enabled us to spend more and more time indoors.

As our day-to-day lives radically changed, building design and indoor visual environments evolved.

Though we are now able to provide adequate artificial lighting day and night, it is well established that daylight and a view to the outside are essential to our wellbeing.

A careful balance between natural and artificial lighting is recognised as the best solution for our comfort and health.

Visual comfort is much further reaching than simply being able to see well enough to perform a given task.

Light has both QUALITATIVE 

To be able to fully describe light, you need to look at its many aspects:

  • its source,
  • its distribution,
  • its tone and colour,
  • its intensity…

Being able to control light levels is also key to visual comfort: both too little and too much light can be a source of discomfort.

Sharp contrast or major changes in light levels can cause stress and fatigue, as the human eye is permanently adapting to light levels.

THE PHYSIOLOGICAL aspect of visual comfort

The human eye is a light-sensitive organ:

  1. A diaphragm (the iris and pupil) adjusts the total quantity of light entering the eye.
  2. A lens adjusts the focus.
  3. Light triggers photochemical reactions in the rods and cones at the back of the retina.
  4. Information is transmitted through bipolar and ganglion cells to the optic nerve and the brain.

Scientists recently discovered that some cells are also responsible for ‘non-visual effects’ on our sleep/wake rhythms, our heartbeat, and the workings of our organs.

So, light has a direct effect on the regulation of various biological functions such as sleep, mood and alertness for example.

THE PHYSICAL aspect of visual comfort
The sun, or an electric light bulb, emits energy…

of which a limited range of wavelength is perceptible to the human eye as light.

The perception of light is determined by the amount of radiation energy that enters the eye and the spectrum of this light.

Light transports information about its own source, whether natural or artificial, and about what it encounters.

THE SOCIO PSYCHOLOGICAL aspect of visual comfort
Light has a profound effect on the way we feel and experience time and space, both consciously and unconsciously.

Our personal history and culture also shapes the way we appreciate light and visual environments.

Extreme variations in preferred range of illuminance exist depending on age and culture.

But whatever the nationality, age or social category, light directly influences the mood and health of us all.

Non-visual effects of light play an important role in this respect. Their discovery is fairly recent and they remain the subject of active scientific research.

The specificities of natural daylight

Natural daylight is the light source to which our eyes are naturally adapted…

so that we nearly always find it more comfortable and attractive than artificial lighting.

In hospitals, daylight accelerates recovery and reduces the need for pain-relief.

In schools it improves alertness and the learning process.

By its variations, it also provides information, maintaining our social and psychological balance.

Spaces lit by daylight appear naturally beautiful and spacious. It plays a major role in defining the aesthetic quality of a space.

Daylight also brings a precious (and free) energy source. However, it can be somewhat unpredictable and difficult to control.

Designing for visual comfort
There is no universal definition of visual comfort as it is a relatively complex issue.

Nevertheless several factors are now commonly accepted as key to designing visually comfortable environments:

  1. Access to views of the outside,
  2. daylight provision in sufficient quantity,
  3. uniform distribution,
  4. and a good combination of natural and artificial light.
  5. adequate task lighting,
  6. control to ensure the absence of glare and high contrasts,
  7. an aesthetically pleasing space.

Building design and choice of materials and equipment also play a significant role.

The size and position of the doors and windows, the orientation of the facades, solar protection devices and the reflectance of the surfaces are some of the tools available to achieve visual comfort.

As our habits continue to change, so will our lighting needs. For example, if reading e-books become standard, the way we light places to read will have to change.

Concerns about energy efficiency and health have brought daylight to the forefront of building design.

However, the benefits of daylighting must not be outweighed by the problems of overheating and glare.

And since daylight varies all the time, a balance has to be found between natural and artificial sources.

So the role of the lighting designer is changing from specifying artificial lighting to understanding natural light. Day-lighting Autonomy helps here.

Active systems to balance light sources have become a lively research field.