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What is visual comfort and how do you achieve it?

The correct amount of natural light in a workspace can improve productivity and reduce eye strain | multi comfort

Visual comfort and daylighting expert, Laura Thuillier, talks about the evolving definition and measurement of visual comfort and how we can design buildings that meet personal preferences and individual needs.

 

How is visual comfort measured?

Visual comfort is usually defined through a set of criteria based on the level of light in a room, the balance of contrasts, the colour ‘temperature’ and the absence or presence of glare.

There are actually many different definitions of visual comfort and what you should measure as part of it.  

At Saint-Gobain, we’ve developed our definition of visual comfort based on what we believe is the best combination of factors to optimise well-being and the feeling of comfort. This includes the quantity and quality of light into a building, quality and access to views from inside the building and the quality of the surrounding space.

This said, visual comfort is very much an emerging field of study and new metrics are proposed almost every day.

The most widely used and accepted metrics tend to focus on:

  • The measure or the quantity of natural light over the year: the potential of a building and its location to provide enough daylight to occupants. This is typically explored through daylight autonomy or useful daylight illuminance
  • The distribution of light as perceived by the eye: whether a space will be too bright or too highly contrasting
  • Others: there are other concepts that don’t have a metric but on which academics widely agree. The quality of the light (through its spectral composition) is one example. The quality of a view is also a consideration but is hard to quantify; however, the first methodologies are starting to appear

Tell us more about how is light measured and how it is perceived by the eye?

Light has different characteristics and can be measured in many ways. One of these is photometry, the science of measurement of visible light in terms of its perceived brightness to human vision, another is radiometry, the measurement of electromagnetic radiation. 

The characteristics and instruments used for measurements will be different depending on the discipline that is chosen to consider light.

In terms of photometry, light can be measured by the intensity of its flux (in lumens) which is typically the unit chosen to quantify the power of a light source, like a lightbulb.

Light can also be quantified by the quantity of light received by a surface, which is the illuminance. It is a marker of how much light is received by a surface. It can also be measured by how much light passes through a solid angle from a surface and reaches a camera (or the human eye for instance), this is the measure of luminance.

In radiometry, light can also be measured by its wavelengths and all characteristics specific to an electromagnetic wave.

Is there a single, universal definition of visual comfort? Or does it vary from person to person? 

The definition of visual comfort is still evolving and not currently set in stone, therefore there isn’t a single universal position on what is comfortable. While it’s something frequently discussed by organisations such as the CIE (International Committee of Lighting) and lighting and daylighting professionals, unfortunately, it’s not that simple.

As well as the definition of visual comfort continually evolving, some things are also subjective and/or dependent on a wide range of factors.

The parameters and maximum light intensity that a human eye can withstand without being damaged, vary based on multiple elements: time of exposition; composition of the light, as well as the colour and age of the eye of the individual using the space.  

Other elements of visual comfort are even more subjective, such as temperature of colour and views. With colour temperature for example, preferences are often cultural[1] so it is impossible to recommend an ideal colour temperature as people will have different feelings and interpretations of it. They will also want to create different atmospheres and narratives with the light.

Similarly, with the view to the outside. It’s fair to assume that most prefer a window to the outside world rather than a windowless room, however not everyone will have the same definition of what is a ‘nice view’.

While there is a lot of subjectivity in visual comfort, there are recommended levels of light or illumination in a building depending on the task performed and on the type of building considered. It’s important to note however that these levels were first defined by ergonomists and are minimum level required to have adequate lighting for vision, so they are levels that ensure one can see without having the make extra efforts, however they are not ‘comfort’ level.

Example of light levels recommended:

Activity

Illumination (lux, lumen/m2 )

Public areas with dark surroundings

20 – 50

Simple orientation for short visits

50 – 100

Working areas where visual tasks are only occasionally performed

100 – 150

Warehouses, Homes, Theaters, Archives

150

Easy Office Work, Classes

250

Normal Office Work, PC Work, Study Library, Groceries, Show Rooms, Laboratories

500

 

Supermarkets, Mechanical Workshops, Office Landscapes

750

Normal Drawing Work, Detailed Mechanical Workshops, Operation Theatres

1000

Detailed Drawing Work, Very Detailed Mechanical Works

1500 – 2000

Performance of visual tasks of low contrast and very small size for prolonged periods of time

200 – 5000

Performance of very prolonged and exacting visual tasks

5000 – 10000

Performance of very special visual tasks of extremely low contrast and small size

10000 – 20000

 

Table taken from: https://www.noao.edu/education/QLTkit/ACTIVITY_Documents/Safety/LightLevels_outdoor+indoor.pdf

 

So how should we design for better visual comfort?

As the measures and definitions of visual comfort continue to evolve, there are two considerations for designers:

Firstly, they should be achieving the above lux levels by utilising natural daylight to light a building as opposed to artificial lighting. This is because natural light is a better source for health and also it has been proven that the eye will adapt to lower levels of illuminance for natural light rather than artificial light.

Secondly and perhaps most importantly, when designing a building to be visually comfortable, control is key. If the occupants can adapt the light to suit their needs, they can achieve their own level of comfort, whatever that may be.

[1]https://www.researchgate.net/publication/236946527_Cultural_Preferences_to_Color_Quality_of_Illumination_of_Different_Objects

Disclaimer: The sole responsibility for any views expressed lies with the author(s). Any opinions shared do not necessarily represent the views of Saint-Gobain.

Laura Thuillier
Laura Thuillier Development Engineer
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