Human Factors 2 Flashcards Preview

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Flashcards in Human Factors 2 Deck (42):
1

Light

electromagnetic waves

2

Amplitude

perceived as brightness (up and down)

3

Wavelength

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

4

Visible light

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

5

Refraction

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

6

Diopter

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

7

refractive power of our eyes

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

8

path of light through the eye

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

9

accomodation

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

10

how we accomodate

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

11

accomodation cond't

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

12

15 diopters of accomodation

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

13

presbyopia

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

14

visual defects

since accomodation isn't instantaneous you can experience defects temporarily

15

myopia

corrected with concave lens
light focused in front of the retina

16

hypermetropia

corrected with convex lens
light focused behind the retina

17

Astigmatism

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

18

Spherical Aberration

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)

19

vergence

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

20

excessive convergence

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

21

Vergence

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

22

downward gaze

requires less vergence for a given horizontal distance than looking forward

23

when working with near objects

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

24

decrease vergence - close object

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

25

minimize accomodation

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

26

visual acuity

dependant on accomodation
ability to discriminate fine detail
tested using letters

27

types of tests

letter target
landholt ring
checkerboard
acuity grating
parallel bars

28

meaning of 20/40 vision

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

29

retina

region of light sensitive receptors

30

rods

light sensitive and responsible for night vision ~120 million

31

cones

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

32

fovea centralis

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

33

light effect on rods and cones

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

34

cone cells

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

35

color blind

deuternomaly - red color blindness is most common at 2.7%
protanomaly is second - see in shades of blue and yellow

36

rods

mostly distributed in the periphery
have less acuity than cones (can't see as detailed)

37

Warnings

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

38

diopter

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

39

max refractive power

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

40

focal length

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

41

astigmatism

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

42

safe limits for light levels

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)