Glare

Question 1

What is Glare?

Answer 1

• Light in wrong place
• Discomfort or impairment of vision experienced when parts of VF are excessively bright in relation to general surroundings
• 2 main types:
  o Disability Glare
  o Discomfort Glare

Question 2

Describe Disability Glare?

Answer 2

• Prevents detection of important details & causes serious loss of visual efficiency (plus discomfort)
• Most likely to occur when there is an area of high luminance close to line of sight
  o E.g. bright sky in front of VDU operator makes screen difficult to read
• ↓ contrast – everything looks bright – causing washing out  whole scene looks grey, can’t see until light adapted
• Like discomfort, disability glare often ↓ by ↑ light level – or putting computer at better angle
  o Car’s headlights on full during day – lots of light and so car’s headlights are less of a problem
  o But if on v dark road w/ no other lighting  much more difficult to drive at night when blinded by car headlights

Question 3

Describe Discomfort Glare?

Answer 3

• Commonest type of glare
  o Causes annoyance but no serious loss of visual efficiency
  o Can impact visual efficiency as makes you feel uncomfortable
• Often only apparent after prolonged exposure  v brightly lit room – feel tired and discomfort
  o E.g. in an airport
• When portion of VF has a much higher luminance than its surround, a feeling of discomfort around eyes and brows may occur
• ↑ w/ an ↑ in luminance of glare source & w/ an ↑ in angular size of glare source at eye
• ↓ w/ an ↑ in luminance of background & w/ an ↑ in angular position of source relative to line of sight
• 45° - forbidden angle

Question 4

What are the 5 types of glare and describe them?

Answer 4

• Direct: when origin is bright source
  o Incorrectly positioned lamp – feel both disability & discomfort glare
  o Angle of light should be >45°
• Reflected: light is reflected from specular or mirror-like surfaces
• Adaptive: range of luminance is too great to be acceptable to eye at any one level of adaptation
  o Every ergonomically designed place of work especially for near work should be designed like this
• Successive: occurs as subject moves from relative darkness to brightness or vice versa
  o Visual system takes time to adapt to its new conditions
   Bright adapting is quicker than dark adapting
• Veiling: reflections are superimposed on object of regard
  o E.g. computer -> move computer

Question 5

What is something to remember about the types of glare?

Answer 5

All types of glare are not mutually exclusive  all interact w/ each other -> may have veiling glare along w/ direct glare as well as others