CHAPTER 22 EYE AND ILLUMINATION

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CHAPTER 22 EYE AND ILLUMINATION
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Anatomy of the eye

• 25 mm / 70 focusing
• Aqueous humor fluid / Glaucoma
• Pupil biconvex lens / diameter varies
• Iris controls amount of light
• Figure 22.1

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Anatomy Concepts

• Accommodation change in the lens shape to vary
  focal distance
• Diopters unit of focal distance
• P(diopters) 1 / f(meters) 1 / S1 1 / S2
• Near point closes point at which you can focus
• Convergence aiming both eyes at same point
• Cones color, daylight, photopic system (figure
  22.4)
• Rods black and white, night, scotopic
  system(figure 22.4)

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Normal Vision

• Normal vision the ability to detect an object 1
  min of arc at 6 m (20 ft., 20-20)
• Visual Acuity ? the ability of the eye to
  distinguish detail.
• VA 1 / Visual angle of minimum object
• detectable, min of arc
• Types minimum separable, minimum perceptible,
  vernier and dynamic.
• Dynamic visual acuity the ability to
  discriminate detail in a moving target.

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Eye Problems

• Myopia nearsightedness, long eyeball the light
  rays from distant objects begin to diverge before
  hitting the retina.
• Solution concave external lens to bring the
  rays farther apart on the eye lens.
• Hyperopia -- farsightedness/ short eyeball the
  light rays from close objects meet behind the
  retina.
• Solution convex lens.

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Eye Problems(contd)

• Astigmatism line focus instead of a point
  focus. Football-shaped eyeballs with unequal
  radii of curvature in two axes.
• Solution external lens with unequal
  curvature. Laser surgery.
• Figure 22.2
• Color weak 0.4 women, 8 men have color
  perception deficiency.

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Light Definitions

• Wavelength and polarization describe the light
  (Table 22.4)
• Radiant power (radiant flux) time rate of flow
  of radiant energy (watts)
• Luminous power the visible part of radiant
  power from a source (lumens, lm)
• Transmittance illuminance transmitted through a
  surface (unitless)
• Luminance a measure of the physical intensity
  of light (lumens/ft2, foot lamberts)
• Brightness measure of the intensity of the
  sensation perceived by the observer

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Light Definitions (contd)

• The attributes of color
• Hue (red, blue) related to wavelength of the
  light
• Brightness (light red, dark red) related to the
  intensity of light
• Saturation (rich full red, pale red) related to
  the purity of light

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Reduction of Visual Problems

• Criteria for lighting a task are the following
• Have satisfactory visual performance
• Minimize cost of lighting
• Have satisfactory esthetics
• Illumination Cost energy cost, fixture cost and
  lamp cost. Cost of illumination is relatively
  lower than labor cost. 90 energy cost / 10
  lamp, most people focus on high initial cost and
  not over the 10-year life.
• Dont save a penny by reducing lighting cost if
  it costs a dollar in reduced labor productivity.

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Performance

• In detecting small targets performance increases
  with increased illumination
• Performance can be easily more improved by
  changing target size and contrast than by
  changing illumination
• Performance on easy visual tasks far exceeds
  performance on difficult visual tasks
• Visual performance is affected by
• Individual differences, quantity of light,
  quality of light and task requirements

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Quantity of Illumination(IES)

• Recommended amount (Table 22.5-22.6)
• General lighting(lighting from the ceiling) the
  amount of illumination depends upon the tasks and
  the occupant age
• Task lighting (local lighting with fixture on
  floor or table) the amount of illumination
  depends on the persons age, speed and accuracy,
  and room reflectance. It should not give direct
  or reflected glare and should light the task

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Sources of light (Table 22.8)

• Low pressure sodium lamp(LPS) poor color of
  light
• High pressure sodium lamp(HPS) poor color of
  light
• Fluorescent colors are distinguishable, and
  permit selection of color
• Metal halide (Mercury) gives good discriminate
  shades of colors
• Incandescent- yellow light, rare

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Luminaries (fixtures)

• Lamps can be put into a wide variety of fixtures.
• Fixtures coefficient of utilization percentage
  of the lamp light inside the fixture distributed
  to work plane
• 5 categories of light distribution from a
  fixture
• Direct, semi-direct, general diffuse,
  semi-indirect and indirect. Most used are direct
  and indirect.

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Quality of illumination

• Glare any brightness within the field of
  vision that causes discomfort.
• Direct comes from windows, lamps, incandescent
  objects and backlighted objects
• Indirect glare caused by high luminance from a
  surface horizontally polarized light.
• Orientation orientation of lights to sharpen or
  blur the surface texture or form of an object is
  called modeling. (Example theatre)
• Esthetics visual qualities of the space
• (Table 22.9)

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Task requirements

• Increasing size increase the size of the
  object, bring object closer to eye, use optical
  aids, working breaks and reorientation of the
  object.
• Increasing contrast can be in either color or
  brightness. Examples photographs, video
  displays, table tops.
• Increasing time work on or inspect stationary
  items rather than moving items. Reduce visual
  obstruction. Have operator face upstream to
  maximize the viewing (in a conveyer line).

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General Lighting

• Uniform Ceiling Lighting light entire area
  uniformly, which allows for flexibility in
  arranging the workspace.
• Zonal cavity method equation
• I(A) CU (LLD) (LDD) (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
• CU coefficient of utilization
• LLD lamp lumen depreciation
• LDD luminaire dirt depreciation

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General Lightning (contd)

• Guidelines for efficient uniform ceiling
  lightning
• A distant light is dim
• Reuse the light
• Use efficient fixtures

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General Lightning (contd)

• Energy Conservation
• Reduced lighting power
• 1. Luminous environment
• 2. Physical environment
• 3. Equipment selection
• 4. Design and maintenance procedures
• Reducing lighting time
• 1. Occupancy
• 2. Cleaning
• 3. Daylight

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Special Lightning

• Lightning for VDT (video display terminal)
• - Paper vs. Screens If the light is uniform
  throughout the area, the amount of light is often
  too much for the screen and too little for the
  paper.
• If task lighting is used, illumination on the
  document can be relatively high and relatively
  low illumination on the screen.

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Special Lightning(contd)

• - Reflections/Glare 8 ways to reduce
  reflection
• 1. Reduce light from windows
• 2. Reduce ceiling glare
• 3. Reduce other brightness sources
• 4. Use barriers
• 5. Tilt the screen
• 6. Change work station orientation
• 7. Consider screen treatments
• 8. Change screen/character background

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Special Lighting (contd)

• - Luminance ratios(characters-to-screen
  background) characters should be 7 times
  brighter than the screen background.
• Inspection lighting in three areas
• Amount of light
• Color of light
• Contrast

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Special Lightning (contd)

• Warehouse Aisle Lighting The use of high racks
  and narrow aisles in a warehouse requires
  high-intensity discharge lamps preferable, since
  it has better directional characteristics. The
  distance from the lamp above the rack should be
  0.5 aisle width, otherwise too much light will be
  wasted.

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Special Lighting (contd)

• Emergency Lighting designed to help people
  evacuate the building if the normal power supply
  fails. It can be provided either by completely
  separate lights with batteries or the normal
  lights with the backup power source.
• Security Lighting
• Offense vs. Defense
• designed to prevent crimes, discourage
  intruders and improve detectability
• Site Considerations
• Large open areas, buildings, perimeter fence,
  entrances, gatehouses, parking.

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Homework Questions

• List the basic criteria for lighting a cast.
• Give 4 approaches to decrease incoming light so
  less is reflected.
• Name the 3 types losses on the zonal cavity
  method equation.
• Is general light enough for inspection? Discuss.