Vision and Lighting

Vision and Lighting

1. Designing a Petrol Pump

   • Visual display
     • Style of display
     • Day/Night use
       • Supplementary lighting needed for the display?
         • Characteristics of the lighting (sodium)
         • 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)

2. 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

3. 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

4. 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)
   • Reflectance
     • % = (Luminance / Illuminance) x pi x 100

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