The Ergonomics of light

Ergonomics

The standard definition of Ergonomics that can be found on Wikipedia and the like goes something like this: "Ergonomics (or human factors) is the scientific discipline concerned with the understanding of interaction among humans and other elements of a system, and the profession that applies theory, principles, data and methods to design in order to optimize human well-being and overall system performance." There's another, less known discipline known as Humanometrics (Anthropometrics) that deals with different geometrical, mechanical, mathematical, physical, chemical and other types of measurements related to the average human.

Lighting quality depends upon both the physical and the psychological parameters of the human being. In general, we can say that good lighting quality exists when a lighting system creates good conditions for seeing, supports task performance or setting-appropriate behaviour, fosters desirable interaction and communication, contributes to situation-appropriate mood, provides good conditions for health, avoids ill effects, and contributes to the aesthetic appreciation of the space.

Lighting quality is not inherent to a space or a lighting design, but to the way the light, or lighting, affects people. This fact cannot be measured, but as indicated above, it is linked to the visual environment, visual comfort and visual performance. Each of these three parameters can be developed further. These factors are interrelated in many ways: especially visual comfort and performance, since they can both be impaired by a phenomenon called glare.

Visual environment

Luminous ambience perception is inherent to people's perception of light. Colour temperatures, colour rendering, light distribution, uniformity, luminaire types – all contribute to the luminous ambience in a space.
 

1. Modelling shape

Lighting has the ability to model shapes at a given point in a space, if the three-dimensional object placed at this point is clearly visible.

The direction and uniformity of the light has a strong impact on our ability to read three-dimensional objects. If an object is seen against a background of similar brightness, it can only be distinguished by the areas of light and shadow created on its surface by the light.

If the light is too diffuse, no shadows are cast and the object looks blurred. If, on the other hand, the light is too strong and direct, the extreme contrasts generated can be unpleasant to the eye and may even give rise to optical illusions. This is important to know in places such as sport arenas and halls where fast ball games are played.

Good modelling is also recommended in public places. People's faces can only be distinguished properly if the light has adequate modelling abilities.

• modelling depends on the light distribution, not on the mean light level
• a combination of diffuse light reflected from light walls and much stronger direct light from a considerably small window will usually create very good modelling.

 

2. Direction of light

The luminous distribution of the luminaires has a strong impact on the modelling ability of the light and the contrasts within the scene. The more direct the lighting, the higher the contrasts. Light striking an object at an angle will emphasise its form and texture more than diffuse light.
 

3. Colour temperature

The correlated colour temperature CCT describes the quality of the light emitted by light sources. It indicates the equivalent temperature that a black body radiator would need to have in order to produce light of the same colour.

The way we feel when placed in an environment with a dominant CCT depends on the brightness of the room. The higher the illuminance, the more comfortable we feel with cool colour temperatures.

4. Shadow

In our three-dimensional world, we perceive our surroundings through form and shapes. Shadow is essentially important to enable us to understand if an object is flat or three-dimensional. Only when our surroundings are easily legible by our brain, can we feel relaxed and comfortable.

Visual performance

Visual performance describes the ability of a person to detect, identify and analyse the details contained in his field of view, taking into account the speed, the quality and the accuracy of his perception.

Visual performance depends, on the one hand, on the inherent characteristics of the task to be performed (dimension, shape, position, colour or reflectance of the details and the background), and on the other hand, on our perception, which is influenced by the lighting conditions (uniformity, glare).

Visual performance is also affected by other parameters such as the respective observer's visual system, external factors that may impede attention, the nature of the background and, more generally, the way that the working space is organised.

 

1. Illumination level

When talking about the quality of light in a working environment, the first question to ask is: "How much light is required?" There are recommendations as to what the minimal illuminance should be. Some of those are provided by the CIE Code for Interior Lighting, but we also have European norms that prescribe minimum values for different situations. The values quoted are based on a healthy 20-year-old observer with good vision. For example, EN prescribes an illuminance of 500 lux between shelves in a grocery store. However, if we consider that the target group for grocery stores comprises people of 40 and more, and if we refer to the next diagram, we can see that values suggested by the norm, differ significantly from those needed in reality (the coloured lines correspond to the age).

1. Uniformity

At night, people are less able to perceive colour, contrast and depth. We know that light is reflected by objects. Therefore maintaining shadow in parts of the streetscape becomes important to enable the cognitive interpretation of our surroundings and to determine the shape of objects and their position in the space. In spite of this obvious fact, lighting standards and regulations require uniform illuminance between poles, in an attempt to replicate daylight conditions and improve visibility. On the other hand, this tends to reduce visual acuity by eliminating contrast, and in fact increases glare by requiring light sources to be mounted higher up on the pole. Experts recommend a pattern of overlapping ovals to provide contrast and promote shadow formation. Human beings are generally more used to non-uniformity and to light-dark contrasts. Uniformity washes out contrasts and shadows generating less interesting environments.

 

Then again, wider spacing between the pole-top luminaires and the creation of pools of light and shadow requires repeated adjustment of the eyes, which may in turn give rise to eyestrain and temporary blindness when entering and leaving the pools of light.

 

2. Glare

Glare is a visual sensation caused by excessive and uncontrolled brightness, such as direct or reflected sunlight or artificial light such as car headlamps at night. Glare is caused by a significant ratio of luminance between the task (that which is being looked at) and the glare source. No matter what space we are concerned with, glare is something that should be avoided. The only difference is if we talk about stage (theatre or concert hall), where glare is a part of the show and is created on purpose.

Glare can be generally divided into two types: discomfort glare and disability glare. Disability glare is the reduction in visibility caused by intense light sources in the field of view, while discomfort glare is the sensation of annoyance or even pain induced by overly bright sources (Rea 2000). When glare is so intense that vision is completely impaired, it is sometimes referred to as dazzle.