Lighting and glare control Flashcards
What are the symptoms that are associated with cataracts?
scattering of light
decreased vision
glare sensitivity
What are the criteria for cataract?
when vision is worse than 6/12 and when the cataracts are interfering with the patients lifestyle
How is illumination measured?
radiometry (measures the entire radiant power and the quantities derived from it) and photometry (measures the part of the radiant power that is perceived by the human eye)
What is radiant flux/power?
radioptic measure of output of light emitted in all directions. Measured in Watts(W)
What is luminous flux?
the output of light source within visible range. Measured in lumens (lm)
What is luminous efficacy?
the ratio of luminous flux to radiant flux. The ratio of the light emitted by a light source within the visible spectrum. measured in lumens per watt (lm/W)
What is luminous intensity?
the perceived power emitted from a light source in a particular direction per unit solid angle. measured in candela (cd)
What is luminance?
the luminous intensity per unit area of light travelling in a given direction. measured in candela per square meter (cd/m2)
What is illuminance?
total luminous flux incident on a surface, per unit are. measured in lux (lx)
What are the laws of radiometry and photometry?
Inverse square of the distance law - light intensity decreases with the square of the distance of the source.
Lambert’s cosine law of illumination -light source not perpendicular to the task surface = illuminance reduced by cosine of the angle with perpendicular plane
What are the types of illumination?
natural light
artificial light
artificial light in general light conditions
artificial light with task illumination
What are the types of light sources?
incandescent - produces light by heating tungsten filament
halogen - whiter light and longer life that incandescent, not as cheap, can get very hot
fluorescent - can be dimmed, doesn’t get as hot
compact fluorescent - smaller - so compact, don’t get as hot, effective - last 8 hrs longer than tungsten, however do give off UV (do not get too close)
LEDs - do not produce heat low light output, produce a blue/white light
What are the types of glares?
Veiling reflections and disability glare and discomfort glare
What is veiling reflections?
high luminance reflections which overlay the detail of the task. usually reduce contrast and cause discomfort. Management - avoid glossy surfaces, use a non-reflective screen, change position of the task and lighting/windows, use additional task lighting to swamp veiling reflections
What is disability glare?
significantly higher luminance than the object of regard causing scattering, decrease in contrast. Management - reduce luminance of glare source, move further away from the line of sight
