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  1. Sens of human eye varies with? (2)
    • wavelength of light
    • lighting conditions (phtotopic and scotopic sensitivity)
  2. Scotopic vision (4)
    • very low light levels 10-6-10-3 cdm-2
    • cannot see colour
    • difficult to see detail
    • peak sens of eye is 507nm
  3. Mesopic vision (2)
    • e.g. at dusk
    • can detect some colour and some detail
  4. Photopic vision
    • at least 10cdm-2
    • can see colour
    • can see detail
    • peak sens of evey is 555nm
  5. Our ability to see depends on factors such as (7)
    • illumination 
    • detail 
    • contrast
    • task difficulty
    • age
    • time needed to complete task
    • aptitude
  6. Coloured light is perceived through _____________
    additive colour mixing
  7. White light is ______
    a combination of all colours in the visible spectrum
  8. Ywllow light is ____________
    a combination of red and green light
  9. Coloured objects are perceived through ____________
    subtractive colour mixing
  10. Coloured _________ is perceived though ___________
    • light - additive colour mixing
    • objects - subtractive colour mixing
  11. What is the colour is observed with subjective colour mixing?
    the colour that is reflected
  12. Blue cloths absorb _______ except ________, which is ___________
    • all colours
    • blue
    • reflected
  13. Black cloth absorbs __________
    all spectral colours
  14. The apparant colour of an object may vary due to ___________
    the wavelength of the incident light
  15. What happens when a blue towel is observed under red light? (3)
    • towel absorbs red light
    • there is no short/blue wavelength in incident light so no light is reflected
    • towel appears black/grey
  16. Light is _________ and it is measured in _____
    • energy
    • Joules (J)
  17. Power is ____________
    the rate of energy flow
  18. Power is measured in
    Joules per second or Watts (W)
  19. Rate of emission of radiation is also known as ______ and is measured in ______
    • radiant flux
    • Watts
  20. Rate of radiation falling on a surface is measured in _______
    Watts per sq metre
  21. Define Lumen (3)
    • amount of light
    • a unit of light similar to watts
    • takes into account the sensitivity of the eye
  22. Define Luminous flux (2)
    • the rate of flow of light energy
    • measured in lumens
  23. What is the luminous efficacy if we have a 100W lamp with a luminous flux of 1360 lumens?
    13.6 lumens per watt
  24. What is luminous efficacy in general terms?
    the efficiency of the lamp
  25. Define relative luminous efficacy (2)
    • related to the photopic sensitivity curve for the human eye
    • watts radiated at 555nm - watts required at another wavelength to produce the same sensation of brightness
  26. Define luminous intensity
    • the luminous flux (amount of lumens) emitted in a particular direction
    • measured in candelas (cd)
  27. Define illumination (3)
    • the amount of light falling onto a surface
    • the number of lumens averaged over a sq metre (lumens/m2)
    • units of measurement = lux
  28. What is the inverse square law of illumination? (2)
    • Illumination = 1/distance2
    • illumination on a surface decreases as the square of the distance to the surface increases (assuming a pt source)
  29. What is the cosine law of illumination?
    if the source is not perpendicular to the surface then illumination = (1/d2)cosθ
  30. Define luminance (4)
    • the brightness of an object
    • the amount of light reflected from an object (paper with print on it, lamp, sun)
    • luminous intensity (cd) in a particular direction / projected area (m2) in a particular direction
    • measured in cdm-2
  31. Illuminance vs luminance
    • amt of light reaching a surface
    • apparent brightness of a surface
  32. How is lumens, illuminance, luminous intensity and luminance related?
    • amt of light
    • per sq m
    • lumens in a particular direction
    • " per sq m
Card Set:
2015-04-17 00:34:27
Env Lighting
lighting prac
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