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The Eye
• 25 mm Sphere
•Light enters through Cornea
•Produces an image on the
Retina through the Pupil
•Iris controls amount of light
admitted
•Accommodation – when the
Ciliary muscle changes the lens
shape to vary focal distance,
measured in diopters =
1/(distance in meters)
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Eye Problems and
Corrections
Nearsightedness
(myopia = long eyeball)
with concave lens
Farsightedness
(hyperopia = short eyeball)
with convex lens
Astigmatism: unequal radii of curvature on two axes of
the eyeball (difficult to correct severe cases) 3
Dark Adaptation
Visible distance in the
dark over time
Retina emphasizes
changes in brightness
more than absolute
levels
Flickering objects
disappear at the critical
fusion frequency (CFF)
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Rods and Cones
Cones: day vision, color,
daylight (TV, full moon, etc.)
Rods: night vision black and
white, night (Snow / Grass
at night)
Rods are more sensitive to
light than are cones.
Cones are more sensitive to
some wavelengths of light
than others.
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Visual Phenomena, called »optical illusions« or »visual
illusions«, the latter more appropriate, because most
effects have their basis in the visual pathway, not in the
optics of the eye
FACTOID:
Did you know that motion sickness is
intimately related to the visual system?
Therapy of motion sickness includes
posture, restriction of head movement,
visual manipulations, concurrent activity,
and drugs
Is the blue wall in front? If you turn
Also, check out:http://www.michaelbach.de/ot
It upside down, the red wall is in front.
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Which UP really points up?
Normal Vision
Visual Acuity: ability of the eye to
distinguish details
=
______________1________________
Visual Angle of Minimum Object Detectable
The ability to detect an object with 1 min of
arc at 6 m (20/20 vision).
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Testing Vision
Measurements:
Gap detection
Spot detection
Lateral displacement of two lines
Dynamic
Dynamic Visual Acuity: ability to
discriminate detail in a moving target,
important for some inspection tasks
Not predicted by static visual acuity
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Eyeglasses
Impact-resistant lenses can still break.
Polycarbonate lenses are light but scratch
easily.
Chemical that reduce light may present a
hazard in welding areas.
Provide protection that contact lenses do not.
Contact lenses should not be used around
chemical fumes, vapors, splashes, or dusty
atmospheres.
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Color Perception Deficiencies
Result from defective pigments in cones.
Influenced by X chromosome, so
females have advantage.
8% of males and .4% of females have
color perception deficiency.
Deficiency may affect red and blue-
green or green and reddish-purple.
Most color-deficient individuals are
color-weak, not color-blind.
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Light Definitions
Luminous Flux (lumen): Light flux, irrespective of
direction from a source
Luminous Intensity (candela): light intensity within a
very small angle in a specified direction; candela = 4Π
lumens
Illuminance = lumens per sq. meter (lux) or per sq. foot
(foot-candle)
Luminance: independent of the distance of observation
= candelas per sq. meter (nit)
Reflectance: percentage of light reflected from a surface
Ex. Mirrored glass = 90%; Black Paint = 3-5%
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Hue, Brightness, and Saturation
Hue: wavelength (observed
color) of the light
Saturation: purity of the light,
from gray to pure color
Brightness: intensity of the light from
extremely dark to none
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Reduction of Visual
Problems
Criteria:
Have satisfactory visual performance
Minimize cost of the lighting
Have satisfactory esthetics
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Criteria
Illumination cost: energy, fixture, and lamp
cost
100 lux for a easy task and
1,000 lux for a hard task
Change target size and contrast
More light will not make the task easier
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Illumination Cost
Energy cost
Fixture cost
Lamp cost
Labor cost is approximately 250 times the
expense of lighting.
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Individual Quantity Individual Differences
Differences Of Light
People vary
Acuity declines with
Visual
Performance
age
Prolonged
performance my
Quality Task
cause fatigue
Of Light Requirements Get eye exams
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Table 23.1
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Quantity of Illumination
Place fixture close to the task
Coefficient of utilization: direct (90% down), semi
direct (90-60% down), general diffuse (60-40%
down), semi-indirect (40-10% down), and indirect
(10-0% down)
Up lighting can reduce brightness contrast and can
lose less light with air flow upward through the
fixture
Beam spread:
Use a wider beam for vertical surfaces, narrower
beam for high mountings, and the shielding angle
should be between 250 and 450
Fixtures should be easy to relocate
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Luminaires - fixtures
Recommended amount
General lighting – ceiling lighting
Task lighting – local lighting
Both physical and psychological needs
Sources
Ideal illumination: free. desired amount on
demand, and high quality
Replacement and restrike time – most bulbs last
over 10000 h; restrike time is the delay after a
power interruption
Color of light
Use metal halide for good discrimination of color
Specify lighting for inspection, especially for
biological goods
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Table 23.6
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Quality of Illumination
Glare
Direct
Indirect
Orientation
Esthetics
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Glare
Four Possible Sources of Direct Glare:
Windows
Lamps
Incandescent Objects
Backlit Objects
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Windows
Have capital and operating costs
Are a source of glare
Are not a practical source of illumination
May admit air
Pass noise and distractions through the
wall
Decrease privacy
Permit a view
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Windows
Change with louvers
or curtains
Change surround
brightness
ex. The splay around
a window
Reorient individuals
so they don’t face the
window.
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Lamps
Point sources like
halogen and
incandescent lamps are
often sources of glare.
Shield at least 25
degrees from the
horizontal (45 degrees
is preferred).
Opaque shields can
also be used.
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Incandescent Objects
These include welding
arcs, lasers, and hot
metal.
Specialized glasses
are required when
exposed to these
sources of glare.
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Backlit Objects
This includes
microfilm and X-ray
readers.
Use an opaque mask
to cover the part that
the film does not
cover.
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Indirect Glare
Horizontally polarized light caused by high
luminance from a surface
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Indirect Glare
Five solutions for indirect glare problems:
1. Decrease incoming light so less is reflected
2. Use multiple low-powered sources instead
of a single high-powered source.
3. Decrease reflectance through matte finishes
4. Filter at the eye.
5. Make your workers move their heads.
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Orientation
Modeling--
orientation of lights
to sharpen or blur
the surface texture
or form of an object.
Light Orientation as
a means of
modifying a
person’s facial
appearance.
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Esthetics
The visual quality of a
space.
Lights can cause various
perceptions.
-uniform vs.
nonuniform
Use lighting controls to
set the “scene.”
-useful for
multifunction rooms
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Task Requirements
Improve the task by
increasing:
Size of objects.
Contrast.
Time.
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Increasing Size
Increase the size of the object itself.
Bring the object closer to the eyes.
Use optical aids.
-How much does the object need to be
magnified?
-Is the aid fixed or does it allow enough
movement for the operator?
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Optical Aids
Options for magnification:
For lower magnification (2-4X) a
lens with a local lighting unit can be
used for most tasks.
Higher magnification (i.e.
microscope) can cause static
fatigue.
Use a closed circuit TV.
Use prescription glasses ground for
the specific task.
Mount magnification on users head
(i.e. surgeon’s loupe).
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Increasing Contrast
But first ….
Why do the University of Tennessee
Volunteers wear orange?
?
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So they can. . .
2) Go hunting on
Sunday.
1) Play Football on
Saturday.
3) Go back to jail on
Monday.
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What’s the point?
The purpose of wearing distinctive
colors is anticamouflage, or improved
contrast (ski)
Improved contrast can be in either color or
brightness.
Use color in text and sign printing.
Use high contrast for printouts, etc.
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Increasing Time
Shoot sitting ducks.
Work on or inspect stationary
items if possible.
Reduce speed if working on
items that move past the
operator at a constant velocity
-Have operator facing “upstream” to maximize
viewing time.
-Remove visual obstructions.
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GENERAL LIGHTING
Uniform Ceiling Lighting
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Methods
Light fixtures mounted on ceiling.
Lights mounted on stands,
with light bounced off the ceiling.
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Advantages
Maximum flexibility in arranging machines
and workstations in the area.
Elimination of the need to move fixtures if
the area is rearranged.
Encourages use of larger lamps, that have
more power.
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Zonal Cavity Method Equation
For uniform lighting, the basic “zonal cavity method”
I (A) = (N1)(N2)(L)
Where
I = Illuminance in area, lux
A = Area illuminated, m2
N1 = Number of fixtures
N2 = Number of lamps/fixture
L = Lumens/lamp
For an area of 3,000 m2 you need 700 lux, you will use
fixtures with 2 lamps each. If each lamp is rated at 20,000
lumens, how many fixtures are needed ?
Answer: 52.5 = 53fixtures
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Modification in Zonal Cavity Eqn
I (A) = CU (LDD)(N1)(N2)(L)
As a rule of thumb, assume CU (LDD) (LDD) =0.5
(modification due to loss of light)
What is the number of fixtures for previous example?
Answer: 105 fixtures
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Guidelines for efficient
uniform lighting
A distant light is dim.
Reuse the light.
Use efficient fixtures.
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Energy Conservation
1. Reduced lighting power
The four subdivisions are:-
The luminous environment.
The physical environment.
Equipment selection.
Design maintenance procedures.
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Luminous environment
High uniform ceiling lighting.
Low uniform ceiling lighting supplemented
with task lighting.
Non-uniform ceiling lighting supplemented
with task lighting.
For high luminescence areas, use lower
levels from general lighting.
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Physical environment
Light is used more effectively if the ceiling
fixture is low.
Use transparent partitions rather than
opaque ones.
Task
Lighting
Wall washing
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Equipment selection
Select efficient lamps, as the cost is 90% for
power, and only 10% for lamps/fixtures.
Efficient luminaries have higher reflectance and
get dirty more slowly.
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Design and Maintenance
Procedures
Consider a mixture of task and general
lighting.
To reduce maintenance cost, consider
group re-lamping.
Clean lamps and fixtures periodically
(say every 2-3 weeks = Preventive Maintenance)
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2. Reducing light time
Occupancy:- Last person leaving the room
should turn lights off.
Cleaning:- Have a “cleaning switch” that
turns on half of the lights.
Daylight:- Certain non-work public areas
can be lighted by daylight, supplemented
by artificial lighting.
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SPECIAL LIGHTING
Lighting for VDTS
Inspection lighting
Warehouse Aisle Lighting
Emergency Lighting
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VDT’s
Video Display Terminal
Since offices have paper and video
screens, we must consider the lighting
for vertical screens, vertical paper (in
document holders) and horizontal paper
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Examples of VDTS
Television
A laptop screen
A computer monitor
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VDTS
Uniform light throughout the work area,
creates a situation where their amount of
light is too much for the screen and to little
for paper
Use Task lighting to fix problems.
If a task involves paper (documents)
illumination should be high and if it involves
screens it should be low.
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Reflection and Glare
Screen reflections can be reduced in eight ways:
i) The first 3 ways reduce light from the source,
ii) the next way is to intercept the light
iii) the remaining 4 ways are to change the
workstation to accommodate lighting.
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Reduce light from source
1.)Reduce light from windows
Vertical blinds
Drapes or curtains
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Reduce light from source
2.)Reduce ceiling glare- Have ceiling fixtures that
have a restricted glare angle
i Use indirect lighting
ii Use task lighting
3.)Reduce other brightness sources
Example. Bright color uniforms or machines.
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Intercept the light
4.) Use barriers- Partitions can block direct light.
Partitions
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Change the workstation
5.) Tilt the screen
6.) Change workstation orientation
7.) Screen treatments- Reflections on a screen
can either be diffused or specular.
Diffuse reflections increase the luminance of
both the screen background and characters,
which reduce contrast ratio.
Spectular reflections a mirror-like image also
occurs. Use a matte treatment to reduce
glare.
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Change the workstation
8) Change screen/character background- a
negative contrast screen might be black
characters on a white screen.
An advantage is that glare is less noticeable.
A disadvantage is it increases flicker
intensity
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Inspection
Consists of
Amount of light,
Color of light
Contrast
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Inspection
Amount of Light- With improved lightening, process
yield improves dramatically, productivity improved, and
quality improved.
Color of light- Perceived object color is affected by
color of light. Specify whether light is incandescent,
and cool white florescent.
Contrast- uses it to detect object shape or object
surface characteristics.
i To detect shape maximize the contrast of
the task and the background.
ii To detect surface characteristics minimize
the contrast of the task against the
background.
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Warehouse Aisle Lighting
Items in a warehouse are stored on racks.
HID (High Intensity Discharge) lamps aid in reading
items on racks.
To reduce visual stress when reading codes:
1. Make bin label large
2. Make container label large
3. Use flood light to read bin
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Emergency lights
The light should discourage intruders (reduce
offense) and improve detectability (Improves
defense).
Offensive vs. Defensive light
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Table 23.9
Emergency
Lights
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Emergency Lights
Site considerations
1. Large open areas- increase in mounting height will
reduce shadows.
2. Buildings -all entry points to the building should be
lighted
3. Perimeter fence- opaque fences should be lighted on
both sides
4. Entrances-lighting should have good color rendering so
the color of people and objects can be discriminated.
5. Gatehouses- lights the inside of the gatehouse dimly.
6. Parking-should have bright light areas.
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