Light and Vision Flashcards
What is the purpose or function of the Cornea, Lens, Retina, Cones and Rods in the human eye
Cornea: Outer lens. Does most of the focusing
Lens: Fine tunes
Retina: layer of light sensitive cells connected to optic nerve. Contains Rods, some cones
Fovea: Contains majority of cones
Cones: allow color vision. High resolution. Low sensitivity to light
Rods: Grant peripheral vision. Less resolution but greater light sensitivty
Function in the dark. Higher sensitivity to light
Describe 3 differences between Cones and Rods
- Color sensitive vs NOT
- High density in central vision/fovea vs NOT
- HIGH resolution vs NOT
What is dark adaptation? Briefly describe the process of dark adaptation.
Eyes switches from cones to rods. Takes time because chemical process has to occur. Over time the rods take over as the main info source to the brain and as a result vision exists with less colour even at the focus point
Why must objects and lettering presented under low illumination be much larger than in daylight conditions?
Bc the rods are in use in dark circumstances, and rods are much lower resolution than cones. Low resolution means letters have to be larger to be made out.
Why should you not use color coding when the illumination is very low?
Rods are in use when illumination is low, and rods cannot see different colours. Cones see colours.
How can you overcome the lack of colour coding in a dark environment when coding lettering?
Use high contrast. Black on white is best to maintain visibility
What is a desirable range of letter size for reading? (In arcmin)
10-25 arcmin.
20 ideal
What is an arcmin?
1/60th of a degree
What is illumination, luminance, reflectance? What devices can be used to measure illumination and luminance?
Illumination: The amount of light falling onto a surface
Luminance: The amount of light reflected by a surface
Reflectance: The capacity for a surface to reflect
Light meters measure illumination
Photo meters measure Luminance and sometimes illumination
What devices can be used to measure illumination and luminance
A light meter measures illumination.
A Photometer measures luminance, sometimes both
How is contrast defined?
As a ratio between the luminance of two surfaces
What is visibility? According to Blackwell, what are the 3 main factors that affect visibility and so how can one improve visibility?
The clarity with which an object can be seen.
Size (visual angle), contrast, illumination.
It can be improved by ameliorating any of these 3 key conditions
What are 5 other factors that affect visibility? Give a sentence to describe/explain each.
Age Target motion exposure time training known location
What is the recommended contrast ratio between the task and large items in workstation? What is the recommended ratio of any adjacent areas in the visual field?
Less than 10:1 for large objects in workstation and main task
Adjacent: Not exceed 3:1
High ratios create glare
What are the 2 design considerations when choosing what light sources to use in a workplace?
Efficiency: Reduce cost
Color rendering- how close is perceived colour to true colour?
Efficient light soures often have fair to poor rendering
How do you determine recommended illumination levels?
Determine the category of work, then determine the weighting factors. Add up the weighting factors. Based on the sums: If -3, -2, use lowest category value If -1,0,+1 use middle category value If +2, +3, use high category value
What is glare? How does glare affect visibility
Glare is excessive brightness in the field of vision. It decreases visibility
Provide 5 ways to reduce direct glare and 3 ways to reduce reflected glare
Reduce Direct Glare:
- Use more light sources w/ lower intensity
- Use light shields, blinds, hoods, diffusing lenses, baffles
- Place work surface perpendicular to light source
- Increase overall background lighting (decrease contrast)
- Place light further from line of sight
Reduce reflected glare:
- Use non-glossy or matte surfaces
- Reorient work surface or task
- Workers wear glasses with polarizing filters
What is phototropism and stroboscopic effect? How can these problems be reduced or avoided
Phototropism is the event of glare distracting someone.
A stroboscopic effect can occur when a piece of moving machinery oscillates in and out of the field of view, bringing an intermittent reflection with it. The moving/flashing glare can distract
In designing a work area, what are 4 ways color can be used?
- Reduce sharp contrasts
- Increase reflectance
- Highlight hazards
- Call attention to other features of the work environment
What is an example of the psychological effect that colour can have?
Warm colours can have people feel comfortable when they would otherwise feel physically cold
