ECE 796/896 Human Factor Engineering

1. ECE 796/896Human Factor Engineering Chapters 16,17,18,19 Light,climate,noise,motion

2. Illumination • 380-780 nm spectrum • Eyes are most sensitive to about 550nm • 2 sources: luminescent + incandescent bodies • Natural color - color of an object under white light. • An object’s color - dominant wavelength, luminance, and saturation

4. Measurement of Light • Photometry - is the measurement of light. • Unit is: Candela (cd) 1 cd = 12.57 lm • 100W bulb = 1740 lm • 1lm/sq.ft. = 1 (fc) foot candle • Lluminance(lx) = (cd)/D2 • Dist. In meters =D

5. Cont. • Reflectance = luminance(fl)/illuminance(fc)

6. Tab16.1

7. Lamps and Luminaires • Luminaire is a device that consists of lamps and components for distributing the light. • Lamp is an artificial light source.

8. Lamps • Two types, Incandescent filament lamp and gas-discharge lamp. • Gas discharge have three types - high-intensity discharge (HID), mercury, metal halide, high pressure sodium, low pressure sodium and fluorescent lamps. • Fluorescent lamps produce ultraviolet that excite a phosphor coating.

9. Cont. • Lamp Color: CRI (color rendering index) • As CRI increases color judgment errors decrease. • Energy Considerations: lamp efficacy amount of light produced per unit of power consumed. • Fluorescent vs. incandescent : lasts 20 times longer, uses 41% less energy, and give 30% more light.

10. Tab16.2

11. Effect of Lighting on Performance • Both field and laboratory studies. • Visually difficult tasks are effected more by lighting levels than visually easy tasks. • Speed improvement noted by over 50% with lighting level changes.

16. Luminance - Glare • Glare is caused by brightness in the field of view that is greater than the luminance to which the eye is adapted, so as to cause discomfort and annoyance. • Direct or reflected glare • Reflected - spread,specular, diffuse,compound.

17. Glare - Cont. • Discomfort, disability and blinding. • Discomfort: A measure Borderline between comfort and discomfort (BCD) The higher the BCD the less glaring was the source or less sensitive was the person. DGR: Discomfort Glare Rating- can be converted to VCP (visual comfort prob)

18. Disability glare • Glare the directly effects visibility and visual performance is Disability glare.

19. Reducing Glare • Reduce direct glare from luminaires. • Select with low DGR, reduce the luminance of sources, position far from line-of-sight, increase luminance around glare source • Reduce direct glare from windows • Set above floors, overhang above window outside • Reduce reflected glare • Keep luminance level low as possible for luminaries, small light sources, diffuse light, use surfaces that diffuse light

20. Computer terminals • 1. Frosting or etching of front surface to reduce specular reflections. • 2. Quarter wave thin-film coatings • 3. Neutral-density filters • 4. Circular polarizers • 5. Micromesh filters

21. Chapter 17 Climate

22. Heat Exchange • Avenues of Heat Exchange: • 1. Conduction: Heat transfer by direct contact. • 2. Convection: Transfer of heat by currents of air. • 3. Radiation: Transmission of heat between objects by electromagnetic radiation. • 4. Evaporation: perspiration converted to vapor.

23. Heat Exchange Equation • DS = (M-W) + - R +- C - E • Where: • DS: = change in body heat content. • M = metabolism, W= work performed, R = radiative heat exchange, C= Convective, and E= evaporative heat loss If the body is in equilibrium -> DS=0

24. Fig 17.1

25. Environmental Factors Influencing Heat Exchange • Air temperature, air flow, humidity, temperature of the surroundings. • Effects of clothing: Insulation provided by air trapped inside the weavings of the fabric. • CLO: measure of insulation necessary to maintain comfort - 70F and 50%. 1 CLO can effect a 16 degree temp change. Eskimo = 12.

27. Measurement of Thermal conditions • Dry-bulb temperature, relatively humidity, hydrometer, wet-bulb temperature, mean radiant temperature, and air velocity.

28. Cont. • Effective Temperature: (et - et*) two indices, combinations of temperature, humidity, air movement that has equal sensation of warmth. ET* has a more complex equation shown on the following graph.

29. 17.2

30. Other Factors • Oxford Index: WD=.85*WB+.15*DB • WB: wet bulb, DB: Dry bulb • Wet-Bulb Globe Temperature: • WBGT = .7*NWB + .3*GT • Botsball: BB = WBGT - 3 degrees

31. The effect of Heat on Work • As external temperature increases, heart rate increases to increase blood flow to the skin to cool. • This can also cause a shortage of blood to muscles and essentially cause a longer amount of time to recovery from work. • Sweat is necessary to when convection and radiation does not cool a person.

32. Heat Illness • 1. Heat rash: • 2. Heat Cramps: • 3. Heat Exhaustion: • 4. Heat Stroke:

33. Cognitive and Perceptual Motor Performance • As temperature - WBGT increases the performance decreases steadily.

34. 17.11

35. 17.12

36. Reducing Heat Stress • Easiest way to reduce heat stress is cool the environment and lower the humidity. • Reducing the energy needed for a task is another way of lowering heat stress.

38. Cold Stress • Most workers that work outside in cool weather can dress properly. Most people who have work related cold weather usually have problems when vehicles break down or they are somehow stranded in the weather without protection.

39. Index of cold Stress - wind chill • Wind chill Index or its derivative, equivalent wind chill index temperature. • Index not used , the modified temp used.

40. Tab17.3

41. Cold Performance • Manual Performance is related to skin temperature. • Tactile Sensitivity: adversely effected by cold.

42. Chapter 18 Noise

43. Sound Level Meter Scales • Meters have scales: A,B,C,D • Psychophysical Indicies: • Physical properties • Psychological properties • Phon: decibel level of the 1000 hz tone

44. Noise of Loss of Hearing • Deafness: Nerve and Conduction. • Nerve deafness is a deterioration of the hairs in the organ of Corti. • Conduction: some blockage of the transmission of sound to the inner ear.

45. Measuring Hearing • 500,1000,2000,3000,4000,6000,8000hz • Presbycusis: hearing loss due to aging. • Sociocusis: hearing due to non-normal cause.

46. Occupational Hearing Loss • Temporary loss from continuous noise: 2 min after the exposure, temporary shift (TTS) . Permanent loss from continuous noise: (PTS) permanent threshold shift

47. Effects of Noise on Performance • General Conclusions: • With the exception of tasks requiring the use of short-term-memory it takes noise in excess of 95db. • Performance of routine tasks show no effect of noise. • If a person has to react to a signal at a definite time, performance will be good even at high noise.

48. Cont. • Visual acuity are not effected by noise. • Motor performance is rarely effected. • Simple reaction time is unimpaired. • Noise tends to have the most effect on continuous tasks without rest.

49. Noise Exposure Limits • OSHA has established noise guidelines • TWA: 8h time weighted average sound level. • Noise dose level of 50 percent ( TWA=85dba) as the ACTION level.

50. Tab 18.3