1 ISE Ch. 20: Vision and Illumination Performance on visual tasks depends on …  human vision  environment  task Human Vision acuity color vision accommodation etc. Task general req’ts specific needs task design Environment light quantity / qualityglare reflectionetc.

2 ISE Human vision: Anatomy of the eye Cones & Rods  Cones provide ______________________.  Rods provide _______________________.  Rods are more sensitive to light than are cones.  Cones are more sensitive to some wavelengths of light than others. (Fig. 20.1, pg. 388)

3 ISE Normal vision Visual acuity = _______________________________ 20/20 vision : ________________________________ Measurements:  Gap detection  Spot detection  Lateral displacement of two lines  Dynamic Dynamic visual acuity  The ability to discriminate detail in a moving target  Important for some inspection tasks  Not predicted by static visual acuity

4 ISE Eye problems & corrections Problems that may affect performance:  Myopia  Hyperopia  Decrease in accommodation range  Astigmatism  Color Perception Deficiencies Corrective lenses & contacts  Eyeglasses provide protection that contact lenses do not.  Impact-resistant lenses can still break.  Polycarbonate lenses are light but scratch easily.  Light-reducing eyeglasses may present a hazard in welding areas.

5 ISE Light Light is described in terms of _______________. Lumens measure ____________. Candelas measure _____________. Lux or footcandles measure ____________.  1 lux = footcandle (fc) Luminance is a measure of the physical intensity of light (footlambert or nit.)  Illuminance (Reflectance) = Luminance Brightness is a measure of the intensity of the sensation perceived by an observer.

6 ISE Color Hue Brightness Saturation

7 ISE Criteria for lighting a task Have satisfactory visual performance.  Individual differences  Quantity of light  Quality of light  Task requirements Minimize cost of the lighting.  Energy cost  Fixture cost  Lamp cost  Labor cost is ~ 250 times the expense of lighting. Have satisfactory aesthetics.

8 ISE Individual differences Visual acuity, resistance to glare, and color discrimination decline with age. Individuals differ greatly in accommodation and convergence capabilities. Prolonged performance may result in fatigue and headaches. Many people do not have the best possible correction.

9 ISE Quantity of illumination Recommended amounts from IESNA  see table 20.5, pg. 397 Sources are measured by cost, amount of light, and quality.  see table 20.6, pg. 399 Luminaires (fixtures) are evaluated on the basis of  Coefficient of utilization  Direct or indirect  Beam spread  Relocatability

10 ISE Windows Have capital and operating costs Are a source of glare Are not a practical source of illumination May admit air Pass noise and distractions through the wall Decrease privacy Permit a view

11 ISE Quality of illumination Color Glare Orientation Aesthetics

12 ISE Task requirements Goal is to enhance the viewed object.  Increase size (magnify)  Increase contrast (use “anticamouflage”)  Increase time (use stationary objects)

13 ISE General Lighting Uniform ceiling lighting  Lights the entire area uniformly.  Allows flexibility in arranging machines and workstations.  Allows use of large lamps.  Zonal cavity method: (I) (A) = (N 1 ) (N 2 ) (L)  Guidelines: Use low fixtures. Reuse the light. Use efficient fixtures.

14 ISE Energy conservation approaches Reduce lighting power:  Luminous environment  Physical environment  Equipment selection  Design and maintenance procedures Reduce lighting time:  Occupancy  Cleaning  Daylight

15 ISE Specific needs: Lighting for VDT areas  Lighting must be designed for vertical screens, vertical paper, and horizontal paper.  Reduce VDT screen glare Inspection  Provide adequate amount of light.  Specify appropriate color of light.  Adjust contrast to bring out shape or surface characteristics.

16 ISE Specific needs (cont.) Warehouse aisle lighting  Consider height of racks  High reflectance Emergency lighting  Minimum requirements  Stairs Security lighting  “target hardening”  Offense vs defense  Site considerations