Visual efficiency & comfort

Visual efficiency and comfort are important considerations in lighting design and architecture.

Visual efficiency refers to the ability of the lighting system to provide adequate illumination for the tasks being performed in the space while minimizing the amount of energy consumed. This can be achieved through careful selection of light sources, luminaires, and control systems that optimize the use of natural and artificial light.

Visual comfort, on the other hand, refers to the subjective experience of the occupants of the space in terms of how the lighting affects their visual perception, mood, and well-being. Factors that can affect visual comfort include the color temperature, brightness, and distribution of the light, as well as glare, flicker, and other visual disturbances.

The level of illumination in a space can affect visual efficiency in several ways. Insufficient lighting can lead to eye strain, fatigue, and decreased productivity, while excessive lighting can cause discomfort, glare, and distraction. The ideal level of illumination will depend on the specific task being performed and the needs of the individuals using the space.

For practical purpose visual efficiency of person depends on level of illumination and ability to see objects in three facet

1. Visual acuity (VA) Sharpness of Vision
2. Contrast sensitivity (CS)
3. Visual performance

Visual acuity (VA)

Visual acuity measured as reciprocal of visual angle ρ (in minutes) subtended at eye by the least perceptible detail

Visual acuity is another important factor that can impact visual efficiency. It refers to the ability of the eye to distinguish fine details and discern shapes and patterns. Visual acuity can be affected by several factors, including age, medical conditions, and environmental factors such as glare and contrast.

In lighting design, visual acuity is an important consideration when selecting light sources and luminaires. High-quality light sources with a high color rendering index (CRI) and color temperature that matches the task being performed can help to enhance visual acuity and improve visual efficiency. Additionally, careful consideration of lighting design factors such as glare control, contrast ratios, and uniformity can also help to support visual acuity and improve overall visual comfort and efficiency

Contrast sensitivity (CS)

Contrast sensitivity =  (Least  perceptible luminence difference (L₂-L₁) / Lower luminence (L₁) ) X 100%

Contrast sensitivity (CS) is another important visual factor that can affect visual efficiency. It refers to the ability of the visual system to detect differences in brightness and contrast between objects and their background.

In practical terms, contrast sensitivity is important for tasks that require the ability to distinguish between objects with subtle differences in brightness or contrast, such as reading text on a computer screen or navigating a dimly lit space. Factors that can affect contrast sensitivity include age, medical conditions, and environmental factors such as glare and illumination levels.

In lighting design, contrast sensitivity is an important consideration when selecting light sources and luminaires. High-quality light sources with a high color rendering index (CRI) and color temperature that matches the task being performed can help to enhance contrast sensitivity and improve visual performance. Additionally, careful consideration of lighting design factors such as uniformity, glare control, and contrast ratios can also help to support contrast sensitivity and improve overall visual comfort and efficiency.

Visual performance

Visual performance time required for seeing expressed possibly as number of characters perceived per second

Visual performance refers to the ability of the visual system to effectively perform tasks that require visual acuity, contrast sensitivity, and other visual abilities. Visual performance can be influenced by several factors, including the level and quality of illumination, the visual environment, and the individual characteristics of the person performing the task.

In lighting design, visual performance is an important consideration when selecting light sources and luminaires. High-quality light sources with a high color rendering index (CRI) and color temperature that matches the task being performed can help to optimize visual performance. Additionally, careful consideration of lighting design factors such as uniformity, glare control, and contrast ratios can also help to support visual performance and improve overall visual comfort and efficiency.

Visual performance is particularly important in environments where visual tasks are critical, such as in healthcare facilities, manufacturing plants, and other industrial settings. In these environments, lighting professionals may need to select light sources and luminaires that are specifically designed to optimize visual performance and reduce visual fatigue and strain.

Glare

Glare considered as a comfort parameter, is the unpleasant effect caused by an excessive contrast of luminance in the visual field. Glare is a condition of vision in which there is discomfort or a reduction in the ability to see significant objects or both due to an unsuitable distribution or range of luminance or due to extreme contrasts in space and time.

Glare is a visual sensation caused by excessive and uncontrolled brightness in a person’s field of view. It can cause discomfort, eyestrain, and visual fatigue, and can even impair vision in some cases. Glare can be caused by a variety of sources, including bright sunlight, reflections from glossy surfaces, and artificial lighting.

In lighting design, controlling glare is an important consideration for improving visual comfort and efficiency. Glare can be reduced by selecting light sources and luminaires that are designed to minimize direct and reflected glare, such as those with well-designed shielding and diffusers. Additionally, careful consideration of lighting design factors such as lighting layout, brightness levels, and contrast ratios can help to reduce the likelihood of glare and improve overall visual comfort.

Glare can be particularly problematic in environments where visual tasks are critical, such as in healthcare facilities, manufacturing plants, and other industrial settings. In these environments, lighting professionals may need to carefully design lighting systems to minimize glare and optimize visual performance.

Achieving both visual efficiency and comfort requires a careful balance between the technical requirements of the lighting system and the subjective needs and preferences of the occupants of the space. This can be achieved through a variety of techniques, such as providing multiple lighting levels and color temperatures, using glare-reducing fixtures and lenses, and designing the lighting system to complement the architecture and interior design of the space.

Achieving visual efficiency and comfort is essential for creating lighting systems that meet the technical and human needs of the occupants of the space. By carefully considering both the technical and subjective aspects of lighting design, lighting professionals can create spaces that are visually appealing, energy-efficient, and supportive of the well-being and productivity of the people who use them.

Day lighting

Illumination in architecture – home page

FD Architect Community Forum Discussion

• Illumination – introduction
• Basic Terminology and Definitions
• Laws of Illumination The Inverse Square Law of Illuminance Illuminance (E) at any poi
• Laws of Reflection and Refraction
• Visual efficiency & comfort
• Day lighting
• Components of Daylight Factor
• Artificial Lighting Design

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