Performance: Lecture 6 Flashcards
Stimulus to the visual system;
The ageing eye 6 things:
- Decreased ability to focus
- Decreased ability to accommodate
- Decreases ability to adapt
- Increased scattering of light
- Yellowing of the lens
- Neural changes
Stimulus to the visual system;
General:
Retinal illuminance
Contrast (luminance and color)
Visual size
Retinal image quality
What is retinal illuminance?
Determines the state of adaptation of the visual system.
NOT amount of light entering the eye
What is the visual size for resolution?
The angle the critical dimension of the stimulus subtends at the eye.
The larger the solid angle, the easier the stimulus is to detect
What is retinal image quality?
Sharp image
By what is retinal image quality defined?
The stimulus itself
Light scattering within the medium through which the light is transmitted
Ability of the visual system to focus the image on the retina
A smaller retina produces a better quality retinal image
Stimulus to the visual system is determined by an interaction between (3 things):
The object to be seen
The background
The lighting of both the object and the background
Why do most people wear glasses?
To improve the retinal image quality
The level of visual performance is determined by:
The stimulus
The operating state of the visual system
Visual tasks have three components:
Visual –> extracting features
Cognitive –> interpreting
Motor –> manipulation of stimuli
Visual comfort is characterized by:
individual differences
context
whole visual field
Four causes of visual discomfort:
Visual task difficulty
Under and overstimulation
Distraction
Perceptual confusion
Specific causes of visual discomfort:
Insufficient light Uniformity Shadows Glare and reflections Flicker
4 Criteria for outdoor views:
Glazing materials
- Min: Clear
- Med: Undistorted
- Max: Neutrally coloured
Outside distance of view
- Min: > 6 meter
- Med: > 20 m
- Max: > 50 m
Horizontal side angle
- Min: 14
- Med: 28
- Max: 54 graden
Number of layers
- Min: Landscape
- Med: Landscape + 1 other
- Max: All layers
Definition of lighting quality
An outcome based definition:
“the extent to which the lighting installation meets the objectives and the constraints set by the client and the designer”
Advantages of outcome-based definitions:
- Results become the measure of success
- Context dependent
- Many physical and psychological processes that influence perception
What are context modifiers for increase of maintained illuminance?
Visual work is critical
Errors are costly
Accuracy
Task area undertaken for a long time
What are context modifiers for a decrease in maintained illuminance?
Task undertaken takes a short time
Task details are of an unusually large size or high contrast
What is the primary design criterion for designing comfortable office lighting?
Illuminance
Tolerances of uniformity depend on (4):
- Absence or presence of windows
- Individual lighting control
- Location of task area
- Context
What is the preferred surround/task area luminance ratio ?
0.1 to 1, with its median at 0.4
What is desired desk reflectance?
0.3
Great variations in luminance distribution leads to:
Constant adaptation of the eyes
User gets tired more easily
The eight forms of glare:
Flash blindness Paralyzing glare Exposure to light bright enough to cause damage Distracting glare Dazzle or saturation glare Adaptation glare Disability glare Discomfort glare
What is the luminance threshold for overhead glare?
16500
The five discomfort glare prediction systems:
- VCP –> visual comfort probability
- CGI –> CIE Glare index
- DGI –> Daylight glare index
- UGR –> CIE unified glare rating
- DGP –> Discomfort glare probability
Differences between VCP CGI DGI UGR
- VCP (1963-1966) –> visual comfort probability
Only for typically sized luminaire sources of light (no halogens or visible skies) - CGI (1969) –> CIE Glare index
Luminaire sources of glare - DGI (1972) –> Daylight glare index
First metric to consider large glare sources: sky through window - UGR (1995) –> CIE unified glare rating
Only for electrical lightsources, no daylight - DGP (2005) –> Daylight glare probability
Direct daylight & specular reflections are considered
What glare rating is mostly used in indoor standards?
Which one most for daylight?
- UGR
2. DGP
Five recommendations to limit glare
- Matte surface finish
- Bright ceiling and bright walls
- Arrangement of luminaires relative to the workspace below
- Luminance restrictions of the luminaire
- Increased luminous area of the luminaires
