Could the lighting affect the identification of the
colour of the pump, signage or display?
Glass/plastic covering, reflections from the artificial
lighting sun or car headlamps?
Height of display for
users (standing/sitting)
How do we see
Light rays from an object pass through the pupil
apeture, lens and inside of eyeball, converge on the
retina. Specific sensors (rods and cones) are
stimulated.
Brain
Controls pupil size
Lens curvature
Eyeball movement
Integrates signals from the eye into a picture (we see)
Pupil
Controls the amount of light
entering the eye
Cornea and Lens
Refracts the rays of light and
focuses them on the retina
Basic Human Vision Capabilities
Visual Acuity
The ability of the eye to
discriminate fine detail
Vernier acuity
Snellen chart
Occurs in the fovea (cones)
Requires accomodation - changes in the curvature
of the lens by contractions of the ciliary muscle
Problems
Myopia
Near sightedness (converge infront of retina)
Hyperopia
Far sightedness - converge behind the retina
Lens can stiffen with age - problems
Increases with better lighting
Contrast sensitivity
The ability of the eye to perceive
differences in illuminaton
Critical for seeing shapes and hazards
Adaption
The changes in our sensitivity to light. Adapting to different
light levels, bright sunshine - x10000000000 brighter than a
dark night- can still see from adaption
Light to dark
Very quick to start - could take
up to 1 hour for full
Dark to light
Quicker- Full takes a few minutes
Vehicles - illuminated instruments (red/yellow light and
night-easier to adjust to) - maintains dark adaption of rods - can
see black, grey, white on roads.
Colour Discrimination
Contrast can vary for different
colour combinations
7-9% males colour deficient (RED-GREEN)
Rods and Cones
Rods
Located through periphery- more
common closer to the lens
More sensitive to light levels than
cones - used for night vision
Cones
In fovea
Need lots of illumination
to operate
Provide visual acuity and colour sensitivity
Eye/Neck/Head movement
Tracking movements
Parameters of Light
Illuminance/Illumination
The amount of light falling
onto a surface (lux)
Luminance
The amount of light emitted from
a surface (candela per m^2)