Light Distribution And Glare Flashcards
is a graphical representation that illustrates the __________________ around the cross- section of a lamp or luminaire.
• It is a curve on a polar graph that shows the relative luminous intensity, in candela,
around the lamp or luminaire
• A cross-sectional map of intensity (candelas) measured at many different angles. It is a _____-dimensional representation and therefore shows data for one plane only.
• The heavy, dark line in the curve represents luminous intensity at various positions beneath the luminaire opening.
• If the distribution of the unit is symmetric:
ꟷ the curve in one plane is sufficient for all calculations.
• If the distribution of the unit is asymmetric:
ꟷ such as with street lighting and fluorescent units, three or more planes are required.
Candlepower ( Candela) Distribution Curve, luminous intensity, two
Categories of Light Distribution Produced By Luminaires:
• ___________
ꟷ ___ to ______% of the light is directed downward for maximum use
• _________
ꟷ ______ to ______% of the light is directed to the ceilings and upper walls and is reflected to all parts of a room or 90 to 100% of the light is directed downward for maximum use.
• Semidirect
ꟷ _____ to _____% of the light is directed downward with the remainder directed upward
• General diffuse/ direct-indirect
ꟷ Equal portions of the light are directed upward and downward
• Highlighting
ꟷ Beam projection distance and focusing ability characterize this luminaire
Direct, 90, 100, indirect, 90, 100, 60, 90
Is excessive brightness in the field of vision that causes discomfort or, in extreme cases, produces a disability from a temporary loss of vision.
ꟷ It is a visual sensation caused by __________ that is sufficiently greater than the luminance to which the eyes are adapted.
ꟷ Glare can be an irritant of or impediment to ______. To prevent the design of lighting installations that produce discomfort, the visual comfort probability is calculated.
Glare, luminance, vision
is a rating of a lighting installation expressed as a percentage of individuals who, when viewing from a specified _________ and in a specified ________, will be expected to find it acceptable in terms of discomfort glare.
• In most spaces, the VCP should exceed %; that is, at least ___% of a statistical group of individuals will rate glare levels acceptable in the space beingmilluminated.
• Guidelines from the ______________________ are used to compute the VCP
location, direction, Visual Comfort Probability, 70, Illuminating Engineering Society of North America
Types of Glare:
• ______________
ꟷ causes visual discomfort without necessarily impairing vision.
• ____________
ꟷ occurs when visibility is impaired from excessive brightness.
• ___________
ꟷ occurs when excessive light enters the eye directly from a light source.
• _____________
ꟷ the result of light entering the eye after reflecting off a glossy
surface. A common type is called a veiling reflection: the reflection
on a glossy surface that impedes seeing such as the reflection on a
computer screen or on a glossy sheet in a magazine.
Discomfort glare
Disability glare
Direct glare
Reflected glAre
- a zone above a 45° angle from the fixture’s vertical
axis.
glare zone
_________ prevent glare and work well in larger spaces such as gymnasiums and conference spaces.
uplights
In small spaces, indirect lighting techniques consisting of________, ________, and _________ lighting installations diffuse light well and prevent glare.
cornice, cove, valance
Properly designed downlights use ________ to prevent light from being thrown into the glare zone.
baffles
Most linear fluorescent fixtures use either a _____ or a ______ to prevent direct viewing of the lamps so direct glare is prevented.
lens , louver
typically made from clear UV-stabilized plastics.
• Clear ______ types include prismatic, batwing, linear batwing, and polarized
lenses
• White translucent diffusers are much less efficient than clear lenses, and they result in relatively low visual comfort probability.
• New low-glare lens materials are available for retrofit and provide high visual comfort (a VCP of 80 or more) and high efficiency.
• Lenses are usually much less expensive but they provide less ______ control than louvered fixtures.
lenses, lens, glare
___________ in a light fixture that create openings for emitting light
• ________ provide superior glare control and high visual comfort compared with lens diffuser
systems.
• The most common application of louvers is to eliminate the fixture glare reflected on ___________.
• Deep-cell parabolic __________ (with 5 to 7 in cell apertures and depths of 2 to 4 in)
provide a good balance between visual comfort and luminaire efficiency
• luminaire efficiency to about ___%. A disadvantage of the deep-cell louver is that it adds 2 to 4 in to the overall depth of a luminaire.
slats, louvers, computer screens, louvers 40
_________ or translucent elements that shield a light source from direct view. They are typically part of the light fixture.
• ________ prevent the light source from throwing light beyond a ___° angle from the fixture’s vertical axis.
• Keeps the light from being broadcast into the glare zone.
opaque, baffles, 30
the amount of light incident on (striking) a surface
illuminance
is the amount of light leaving an object, thus relating to how bright an object appears to the human eye.
ꟷ An object may be illuminated, but the eye cannot see it without visible light leaving (reflecting off) the object in the direction of the viewer.
ꟷ The luminance of a surface is equal to the _____________.
luminance, reflected illuminance
a LUMINOUS INTENSITY of a surface in a given direction per unit of projected area of the surface.
luminance
It is the density of LUMINOUS FLUX striking a surface.
• It describes how bright a surface may appear to the human eye depending upon the surface’s reflectance.
• The appropriate units of measurement for illuminance are the _______ and ________.
illuminance, lux, foot-candle
One foot-candle is roughly equal to ___ lux:
10
The SI (metric) unit for illuminance, which is ONE LUMEN of light uniformly illuminating a ONE SQUARE METER surface (lm/m2).
• ______ incident on a surface are related to the lumens (lm) striking the surface
and the area of the surface (A), in m2: E lm/A.
lux
ꟷ________ lighting installations that consumes lot of energy (electricity and cooling) or too much lighting that is not necessary in a building interior should be avoided.
ꟷit is wasteful because of higher investment (cost), maintenance, and energy.
ꟷCost that is enough to light is better
Large
___________ (measured in footcandles) or in terms of lumens per square meter or lux.
light intensity
Light Output is measured in _____.
lumens
For ambient lighting in public and working spaces.
Categories A through C
For common visual task requiring more difficulty.
Categories D through F
For prolonged, visually demanding task.
Categories G through I
In General, recommended lighting levels decrease as the size and contrast of the visual task increase ( T or F)
F, baliktad ang decrease and increase
the recommended lighting level will be near the
lower level of the range when the size and/or contrast of the visual task is large and will be near the upper level of the range when the size and/or contrast of the visual task is small
fun fact
In Lighting design
• E is used as a symbol for ________
• I is the symbol for __________
illuminance
luminous intensity
Illuminance (E) is the density of ________, the intensity of light on a surface.
luminous flux
states that the illuminance at a point on a plane
perpendicular to the line joining the point and a source is inversely proportional to the square of the distance between the source and the plane.
inverse square law
states that illuminance (E) at a point on a plane is
proportional to the cosine of the angle of light incidence, where the angle of light incidence is measured between the direction of the incident light and the normal to the plane of the surface.
cosine law of incidence
average illuminance at a reference work plane.
target illumination
usually horizontally positioned, at which work is performed and on which the illuminance is specified and measured.
• ___ fc may be acceptable on the floor of a lobby
• ___ fc on a table in a conference room
• ___ fc on tables in a drafting production area
Work plane
15
30
75
is the currently accepted method for calculating average illuminance levels for indoor areas unless the light distribution is extremely ________. The basic principle behind this method is that foot-candles at the work plane are equal to _______ over the work plane.
zonal cavity method, asymmetric, flux
The space between the luminaires and the work plane is referred to as the ___________; the space between the work plane and the floor is called the __________; and the space between the ceiling and the luminaires (if they are suspended) is defined as the ____________.
room cavity, floor cavity, ceiling cavity
Once the number of luminaires (#) required for uniform illumination has been determined, the luminaires must be arranged. ___________ and ________ luminaires generally cast light evenly in all directions, which permits uniform spacing in even rows and columns, although even rows and offset columns may be used. _______________ luminaires generally require spacing that is greater perpendicular to the axis of the lamps versus parallel with the lamps. To ensure uniform illumination of the work plane, luminaires cannot be spaced too far apart.
HID, incandescent, tubular fluorescent
The ______________ ratio is an approximate maximum ______________ height ratio required to ensure uniform illumination on the ________. It is used as
a conservative guide to determine maximum center-to-center luminaire spacing.
spacing criterion, spacing-to-mounting, work plane
TYPE OF GLAZING MATERIALS
historically, only _______ was used as a glazing material
glass
