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Ergonomics
3.0 Illumination: Basic Guidelines
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Basic Guidelines
(I) Intensity
of Light Source
Amount of electromagnetic energy radiated by a light source
UNITS
Candela
(E) Illuminance
Amount of light falling on a surface
UNITS
Foot-Candlels or Lux
Amount of light falling on surface is same wherever on surface
Inverse Square Law
Illuminance is inversely proportional to squared distance
E = I/(D^2)
Measurement Tools
Illumination Meter
(L) Luminance
Amount of light reflected off by a surface
UNITS
Foot-Lambert
Amount of light reflected depends on location (color, darkness)
Measurement Tools
Photometer
Calculating Luminance
L = R*E
Luminance = Reflectance * Illuminance
Reflectance
Ratio from 0 to 100%
Contrast
Difference between the luminance of light and dark areas
C(%) = (L-D)*100/(L+D)
Cobb Moss Curve
Represents quantitative relationship between contrast ratio, luminance, and visual angle
Measurement
can be measured by grating - determining the spatial frequency (the number of dark-light pairs that occupy 1 degree of VA that someone can detect
Contrast Sensitivity
the reciprocal of the minimum contrast between a lighter and darker spatial area that can just be detected.
Influences
Level of contrast
Level of illumination
Age of eye
Motion
Simultaneous Contrast
The tendency for some hues o appear different when viewed adjacent to other hues
Note
Description
Cobb Moss Problems
Draw a curve for luminance if it isn't already drawn.
Always draw for lighter luminance
See equation for visual acuity above
If VA is below min VA, an observer canno see it
Multiply MVA axis by 2 to get 95% accuracy
Use contrast ratio equataion
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