Light and Vision

Question 1

What is the purpose or function of the Cornea, Lens, Retina, Cones and Rods in the human eye

Answer 1

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

Question 2

Describe 3 differences between Cones and Rods

Answer 2

• Color sensitive vs NOT
• High density in central vision/fovea vs NOT
• HIGH resolution vs NOT

Question 3

What is dark adaptation? Briefly describe the process of dark adaptation.

Answer 3

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

Question 4

Why must objects and lettering presented under low illumination be much larger than in daylight conditions?

Answer 4

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.

Question 5

Why should you not use color coding when the illumination is very low?

Answer 5

Rods are in use when illumination is low, and rods cannot see different colours. Cones see colours.

Question 6

How can you overcome the lack of colour coding in a dark environment when coding lettering?

Answer 6

Use high contrast. Black on white is best to maintain visibility

Question 7

What is a desirable range of letter size for reading? (In arcmin)

Answer 7

10-25 arcmin.

20 ideal

Question 8

What is an arcmin?

Answer 8

1/60th of a degree

Question 9

What is illumination, luminance, reflectance? What devices can be used to measure illumination and luminance?

Answer 9

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

Question 10

What devices can be used to measure illumination and luminance

Answer 10

A light meter measures illumination.

A Photometer measures luminance, sometimes both

Question 11

How is contrast defined?

Answer 11

As a ratio between the luminance of two surfaces

Question 12

What is visibility? According to Blackwell, what are the 3 main factors that affect visibility and so how can one improve visibility?

Answer 12

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

Question 13

What are 5 other factors that affect visibility? Give a sentence to describe/explain each.

Answer 13

Age
Target motion
exposure time
training
known location

Question 14

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?

Answer 14

Less than 10:1 for large objects in workstation and main task

Adjacent: Not exceed 3:1

High ratios create glare

Question 15

What are the 2 design considerations when choosing what light sources to use in a workplace?

Answer 15

Efficiency: Reduce cost

Color rendering- how close is perceived colour to true colour?

Efficient light soures often have fair to poor rendering

Question 16

How do you determine recommended illumination levels?

Answer 16

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

Question 17

What is glare? How does glare affect visibility

Answer 17

Glare is excessive brightness in the field of vision. It decreases visibility

Question 18

Provide 5 ways to reduce direct glare and 3 ways to reduce reflected glare

Answer 18

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

Question 19

What is phototropism and stroboscopic effect? How can these problems be reduced or avoided

Answer 19

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

Question 20

In designing a work area, what are 4 ways color can be used?

Answer 20

• Reduce sharp contrasts
• Increase reflectance
• Highlight hazards
• Call attention to other features of the work environment

Question 21

What is an example of the psychological effect that colour can have?

Answer 21

Warm colours can have people feel comfortable when they would otherwise feel physically cold