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Eye

 


    Visual Acuity
     
PROBLEM  

SOLUTION

Generalized decrease in ability to see objects and details clearly    1.  Provide appropriate product illumination and contrast.

The light on visual displays, particularly for typography and control information, should provide good legibility while using the product (e.g., operating controls and reading operating instructions.)

It is important to have the source of illumination positioned at a low angle to the surface in order to prevent glaring reflections along the operators line of light.

Environmental lighting should allow the product's form and surfaces to be easily "read." The lighting should develop a contrast between an object and its background in order to separate the product's form and features from the immediate environment.

     
    2.  Consider the object's environment.

Design to accommodate known or suspected environmental conditions such as poorly lit enviroments, distracting textures, and visual clutter.

Isolate priority information from enviromental background value, clutter, and glare by selecting the appropriate color, value, size, and chromatic intensity for type, graphic symbols, and their respective fields.

 

 

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    Visual Accommodation 
     
PROBLEM   SOLUTION
Specific decrease in abiity to focus on nearby objects or read fine print (presbyopia).   1.  Minimize the need for  typography.
 


In many cases, typography can be eliminated, or at least minimized, by substituting simple, unequivical, graphic symbols.

When used they should be sized and positioned to communicate the importance, order, and relationships of the product's components, controls, and operating sequence.

Irrelevant information and decoration (e.g., nameplates, logos, and extraneous decorative elements) should be eliminated from informational surfaces.

     
    2.  When typography is essential for information purposes, make it legible.

In general, select the largest appropriate size and weight of type that will serve the intended purpose, and the widest appropriate letter, word, and line spacing that will ensure legibility.

Favor san-serif type for non-text material, such as display type, headings, and numbers.

For maximum readability, use upper and lower case type and isolate individual information messages where accurate communication of information is important (e.g., control settings and instructions), determine the size of the type by the expected level of illumination and viewing distances.

Strive to maximize the contrast between the type and its field, and avoid using ornate, decorative, or segmented type faces.

In order to provide clear and unambiguous visual messages, use redundant cuing when possible by combining type with graphic symbols.

On dials, use only whole numbers and a minimum of markings.

 

 

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    Visual Threshold 
     
PROBLEM
  SOLUTION
Difficulty in seeing objects in dim light   1.  Provide adequate illumination.

Maintain a visually adaptable environment by providing at least the minimum professionally recognized foot-candle measurement standards for detail work, general office work, instrumentation, general lighting, and emergency lighting.

When possible, provide the operator/user with adjustable control of the lighting environment (e.g., rheostats, adjustable shades, or changeable filters).

 
    2.  Illuminate to reveal contour of form.

Changes in surfaces may be difficult or impossible to perceive under certain ligting conditions (e.g., flat lighting or dim lighting).

In order to perceive a product's form and/or reveal its contours, the environmental lighting level should be maintained at one third that of task lighting.

Where it is important to clearly reveal or communicate the contour and/of texture of a particular surface, locate the light source at a low angle to that surface.

 

 

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    Brightness Adaptation 
     
PROBLEM
  SOLUTION
Inability of the eye to adapt to excessively bright light or surface   1.  Reduce excessive illulmination.  

Provide illulmination with intensity levels that are appropriate for the indtended use and in line with professionally recognized standards.

Provide for a gradual change in light levels between widely differing levels of illuminated surfaces and environments.

 
    2.  Avoid over-saturation of illumination.

Eliminate "hot spots" by ensuring that critical information is evenly illuminated.

Avoid using spot lights for general illumination. Favor indirect light where appropriate.

 
 
 
Eye loses its ability to distinguish between dark and light surfaces.   3.   Provide maximum appropriate contrast.

Ensure that all critical information is evenly illluminated and isolated from competing background clutter, color, textures, and glare.

Make critical indicators stand out from among other displays by providing contrasting values, colors, and textures.

Whenever possible, offer the operator a means to control the level of contrast.

Where dark adaptation is required (e.g., darkrooms, night lights, etc.), use red illuminants.

 

Difficulty in adjusting to bright lights (glare).

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4.  Eliminate glare.

Present information in a non-glare mode by offering non-reflective surfaces, providing adjustable illumination, and designing appropriate shielding of viewing surfaces. Also consider the use of polarizing screens.

 

 
    Critical Flicker Frequency
     
PROBLEM   SOLUTION

Flashing light may be perceived as steady.

 

  Exercise care in the use of flashing lights.

Use flashing lights only for specialilzed applications  (e.g., warning or attention). If flashing lights must be used, use a slow rather than a fast flash (do not exceed 15 cycles per second).

Once flashing begins, maintain the flashing in order to provide a sense of distance between the viewer and the flasher.

Ensure that the color, intensity, and frequecy of the flash is in marked contrast to the backgrouond environment.

 

 
    Hue Perception
     
PROBLEM
  SOLUTION

Inability to differentiate cool colors (green / blue / violet).

 

 

  1.  Maintain color contrast.

Avoid using green/blue/violet color combinations.

If such combinations must be used, use them with care and ensure that each color contrasts the others in value (e.g., light vs. dark) and/or chromatic intensity (bright vs. dull).

Strive for color combinations which use strongly contrsting colors (e.g., yellow/blue).

When developing and using color-coding systems, avoid confusioon and misunderstanding by applying the system in a clear, consistant, and unambiguous manner.

In applications were sharp vision is critical, avoid using blue illuminants.

 

Increased perceptual blending of analogous colors.

 

 

 

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  2.  Maintain value contrast.

Avoid using analogous color combinations like red/orange or violet/red.

If such combinations must be used, use with care and develop an artificial value contrast wich ensures that each color contrasts the others in value (e.g., light vs. dark) and/or chromatic intensity (bright vs. dull).

It is particularly important to develop high contrast where accuracy in speed and reading are required (e.g., instructions and warnings).

 

 

 
    Chromatic Perception
     
PROBLEM   SOLUTION
Decresed ability to see color.   1.  Avoid the use of low chromatic (dull) color when color identification is required.

It is important that high chromatic (bright) colors be used for identity applications (e.g., color coding, color identification, and color differentiation).

When high chromatic colors cannot be used, use color with care. Strive for colors that contrast in value     (light vs. dark) and/or contrasting colors (e.g., yellow/blue).

When developing and using color identification systems, avoid confusion and misunder-standing by applying these systems in a clear, consistant, and unambiguous manner. In applications where accurate color reading is important, use white light as the illuminant.

 
    2.  Maintain value contrast.

Avoid using colors of similar value contrast in side-by-side or figlure/ground applications.

If such positioning must be used, use with care and develop an artificial contrast which insures that each color contrasts with the other(s) in value (e.g., light vs. dark) and/or chromatic intensity (gright vs. dull).

It is particularly important to develop high contrast where speed and reading accuracy are required (e.g., instructions and warnings).

 

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    Field of Vision
     
PROBLEM   SOLUTION
Loss of peripheral vision (tunnel vision).   Accommodate a decreased field of vision.

It is important that critical information, caution or warning lights, and sets of analogous controls be clustered within the operator's narrowest appropriate cone of vision.

Clustering minimizes the necessity for shifting the operator's vision while working through a sequence of control operations.

Cones of vision should be located to correspond to the logical (natural) sequence of the operation.

 


Rationalizations can no longer excuse designs of products or environments that fail to attract and accommodate any segment of the population.

 



*Courtesy of "Guidelines and Strategies for Designing Transgenerational Products," was suported, in part, by Grant number 90-AT-0182, from the Administration OIffice of Human Development Services, Department of Health and Human Services, Washington, DC 20201, and the All-University Gerontology Center, Syracuse University.

 



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