Lecture 14 - Human Factors 2 Flashcards
Light is an _________ wave.
electromagnetic
________ is perceived as brightness.
Amplitude
___________ is perceived as hue.
wavelength
________ is the change in direction of propagation of a wave due to a change in its transmission medium
refraction
A lens that can focus parallel light rays to a point 1 meter from its axis has a refractive power of ____ diopter.
1
Our eyes have a refractive power of ____ diopters when viewing distant objects.
59
The _______ contracts and expands to adjust the amount of light entering the eye.
Pupil
To focus for near objects we need to (increase/decrease) the refractive power of the lens.
increase
What is fatiguing about accommodation?
Contraction of ciliary muscle
When the muscle is relaxed, the _______ ________ pull the lens back into a thinner flatter shape.
suspensory ligaments
_______ = far objects are blurry
myopia
_______ = near objects blurry
hypermetropia
_________ = refractive error due to an unequal curvature of the refractive surface (either cornea or lens)
Astigmatism
________ ________ = outer regions of the lens focus light at a point slightly ahead of the mid portion of the lens, causing vision to be blurred.
spherical abberation
Objects that are very _______ require muscle contraction to enable the eyes to converge (and focus via accommodation) on the object.
close
Since we are least sensitive to ______ we can illuminate a room or sign with this colour and not worry about _______ out our ability to see in dark environments.
red; bleaching
_______ _____ = as we switch from cone to rode vision (day to night) shorter wavelengths appear brighter (_____ objects appear brighter, _____ objects appear darker).
Purkinje Shift; green; red
Is night or day vision more sensitive?
Night
Our most sensitive light ranges are _______-_____ light during daylight and _______ light at night.
yellowish-green; green
Blue light affects levels of the sleep-inducing hormone ________ more than any other wavelength.
melatonin
Retinal ganglion cells contain _______ which is sensitive to blue light and can modify your circadian rhythm.
melanopsin
One _____ = one lumen per square meter.
lux
A common candle emits light with roughly ___ cd luminous intensity.
1
What are the 5 main causes of lighting problems?
- Insufficient light
- Glare
- Improper contrast
- Poor distribution
- Flicker
Performance time _____ with increasing amount of illumination, and error _____ as well.
decreases
What are the two types of glare?
- Direct
2. Indirect
What are the two types of indirect glare?
- Specular (smooth)
2. Diffuse (matte)
What are the 3 effects of glare?
- Discomfort
- Disability
- Blinding
_______ = natural tendency to gaze at bright objects.
Phototropism
Lamps operating on alternating current produce light flickering at a frequency of ______ Hz.
120
People can see lights flashing on and off up to about ____ flashes per second (____ Hz)
50
_______ = accommodation decreasing with age, to the point where we can’t anymore.
presbyopia
With _______, light is focused in front of the retina, and it is corrected with a concave lens.
Myopia
With ______, light is focused behind the retina, and it is corrected with a convex lens.
hypermetropia
The typical eye has +0.__ microns of spherical aberration.
0.15
Natural distance where _______ becomes necessary changes with gaze angle.
vergence
What distance should an object be when looking ahead? When looked 45 degrees down?
1m; 80 cm
We have (more/less) accommodative power when we gaze downwards.
more
Objects right at point of _______ will cause constant adjustments rendering them in and out of focus.
accommodation
A person with 20/40 vision can detect a critical detail at ___ feet that a normal person could detect at ____ feet.
20; 40
Night vision = ______; day vision = ______; dusk vision = _______.
scotopic; photopic; mesopic
Protanopia and deuteranopia = seeing in shades of what two colours?
blue and yellow
_______ _____ (cd)= total light emitted by a source.
luminous flux
________ (Lm/m^2) = light falling onto a surface
illuminance
_________ (cd/m^2) = light reflected by a surface
luminance
What are 5 common health effects associated with poor lighting?
- Headache and eyestrain
- Neck, back and shoulder strain
- Falling tripping and slipping
- dropping materials and tools
- Depression
With _______ reflection, viewer sees a reflection at only one point.
specular
With _____ reflection, lights from all points on the surface reach the viewer.
diffuse
What are 3 ways to decrease display refection?
- Blinds
- Indirect lighting systems
- Low wattage direct light on documents
When light hits a flat surface, some of it becomes horizontally polarized with causes ______.
glare
Only safe, _______ polarized light passes through specially treated polarized sunglass lenses.
vertically
What is a way to combat the headaches, eyestrain and general eye discomfort reported by people working in fluorescent lighting?
use a high frequency electronic ballast of 20,000 Hz or higher
With colour and perception, we basically can only identify the colours we can ______.
name
