Human Factors 2

Question 1

Light

Answer 1

electromagnetic waves

Question 2

Amplitude

Answer 2

perceived as brightness (up and down)

Question 3

Wavelength

Answer 3

(nm) perceived as hue or color shift (horizontal, side to side)

Question 4

Visible light

Answer 4

visible light is 400-700nm
400 = blue
500 = green
700=red

Question 5

Refraction

Answer 5

the change in direction of propogation of a wave due to change in its transmission medium

Question 6

Diopter

Answer 6

a lens that can focus parallel light rays to a point 1meter from its axis has a refractive power of 1 diopter

Question 7

refractive power of our eyes

Answer 7

59 diopters when viewing distant objects (48from the cornea)

Question 8

path of light through the eye

Answer 8

enters the eye its refracted through the cornea and the lens is focused on the retina
- the pupil contracts and expands to adjust the amount of light entering the eye

Question 9

accomodation

Answer 9

to focus for near objects we need to increase the refractive power of the lens

Question 10

how we accomodate

Answer 10

contraction of the ciliary muscle enables the lens to become rounder and have more refractive power ( fatigue causing)

Question 11

accomodation cond’t

Answer 11

when the muscle is relaxed the suspensory ligaments pull the lens back into a thinner flatter shape

Question 12

15 diopters of accomodation

Answer 12

this decreases with age to the point where we cannot accomodate anymore

Question 13

presbyopia

Answer 13

farsightedness - when we no longer have the ability to accomodate (normally can 15diopters)

Question 14

visual defects

Answer 14

since accomodation isn’t instantaneous you can experience defects temporarily

Question 15

myopia

Answer 15

corrected with concave lens

light focused in front of the retina

Question 16

hypermetropia

Answer 16

corrected with convex lens

light focused behind the retina

Question 17

Astigmatism

Answer 17

refractive error due to unequal curvature of the refractive surface (either cornea and or lens)

Question 18

Spherical Aberration

Answer 18

outter regions of the lens focus light at a point slightly ahead of the mid portion of the lens causing vision to be blurred ( little distorted but top down control can fix it so we barely notice)

Question 19

vergence

Answer 19

objects that are very close require muscular contraction to enable eyes to converge and focus via accomodation on the object

Question 20

excessive convergence

Answer 20

at a work station excessive convergence causes fatigue and muscle imbalances to occur making the task more difficult and causing strian

Question 21

Vergence

Answer 21

natural distance where vergence becomes necessary changes with gaze angle (up/down)

Question 22

downward gaze

Answer 22

requires less vergence for a given horizontal distance than looking forward

Question 23

when working with near objects

Answer 23

minimize the vergence - the closer the object the lower it should be (minimize effort)

Question 24

decrease vergence - close object

Answer 24

1m when looking ahead 80cm when looking 45degrees down

Question 25

minimize accomodation

Answer 25

objects right at the point of accomodation will cause constant adjustments rendering them in and out of focus - we have more accomodative power when gazing down

Question 26

visual acuity

Answer 26

dependant on accomodation
ability to discriminate fine detail
tested using letters

Question 27

types of tests

Answer 27

letter target
landholt ring
checkerboard
acuity grating 
parallel bars

Question 28

meaning of 20/40 vision

Answer 28

a person can detect a critical detail at 20feet that a person with normal vision could detect at 40 feet

Question 29

retina

Answer 29

region of light sensitive receptors

Question 30

rods

Answer 30

light sensitive and responsible for night vision ~120 million

Question 31

cones

Answer 31

color sensitive cells densly located in the fovea provide photopic vision ~ 6 million

Question 32

fovea centralis

Answer 32

small, central put composed of closely packed cones in the eye in center of macula responsible for sharp central vision - necessary for visual detail reading and driving

Question 33

light effect on rods and cones

Answer 33

light entering the eye triggers photochemical reaction in rods and cones at back of retina
-chemical reaction in turn activates bipolar cells

Question 34

cone cells

Answer 34

3 types of cells with sensitivity to different wavelengths

• any given color is perceived by the distribution of firing
• color blindness is one of set of cells is missing

Question 35

color blind

Answer 35

deuternomaly - red color blindness is most common at 2.7%

protanomaly is second - see in shades of blue and yellow

Question 36

rods

Answer 36

mostly distributed in the periphery

have less acuity than cones (can’t see as detailed)

Question 37

Warnings

Answer 37

should flash instead of change color because we can’t identify color well in our periphery because its mostly rods

Question 38

diopter

Answer 38

has to do with ability to refract - happens where the signal crosses over - somewhere behind the lense - the focal length

increase refractive power we shorten the focal length
shorter distance to flip image in our eye before we percieve it

Question 39

max refractive power

Answer 39

15diopters
squeeze the lense make it more curved - cicilary muscles to squeeze it down into more of a sphere and increase refractive power - accomodation

Question 40

focal length

Answer 40

the reciprocal of your diopter

if you want refractive power its the reciprocal of the refractive power

Question 41

astigmatism

Answer 41

mis-shapen lense - can still focus it just takes longer not

spherical aboration

Question 42

safe limits for light levels

Answer 42

200-500 lux working range for an office setting
if your doing something with high concentration can up the lux but want to reduce glare
non reflective surfaces - anti glare screen
sunglasses - polarize film and alignes all light waves vertically that way (clean glare free image)