Lighting & Acoustics Flashcards
Definition of light
visually evaluable radiant energy
visible spectrum on EM radiation
Coefficient of transmission
total light transmitted through a material
clear glass = 85% transmittance
translucent = transmits light, but not a clear image
Reflectance/reflectance coefficient
ratio of total reflected light to total incident light
reflection can be specular (mirror-like), diffuse (from uniformly rough surfaces), or combined (brighter and duller points)
Eye parts to process light
cones perceive detail and color, more near the fovea
rods perceive motion and light, surround the fovea
Candlepower
unit of luminous intensity that is equal to horizontal output of a wax candle
aka candela
radiant energy output
Illuminance
density of luminous flux incident on a surface (lumens per unit area)
one lumen uniformly incident on 1 sq ft = 1 foot-candle (fc)
radiant energy shining on a surface
Lumen
(lm) = the unit of luminous flux equal to a unit solid angle of 1 steradian (square radian, like a 3D ray) from a uniform point source of 1 candlepower
radiant energy in a given 3D shape
Luminance
the luminous flux per unit of projected/apparent area and unit solid angle leaving a surface, either reflected or transmitted, unit of candela/sq meter or nit, or US system, footlambert (fL)
aka brightness w/o subjectivity of pupil adjustment
how much illuminance from a lumen
Luminous intensity
solid angular flux density in a given direction
measured in candlepower or candelas
how much radiant energy, non geometrically defined
Illuminance targets
set by IESNA, Illuminating Engineering Society of North America
based on ppl 25-65 yrs old
for older, double values,
for younger, half the values
restricted overall for efficiency, set in watts/sq ft
Glare
direct (bright light source) and reflected (off a surface), aka veilng glare (reduces contrast)
both worse when surrounding area is dark
visual comfort probability (VCP) metric used to evaluate glare = percentage of viewers likely to experience discomfort
direct glare comes from more horizontal light (so cut off at 45 deg), reflected glare from more perpendicular (so make angles of incidence and reflection unequal)
Contrast
difference in illumination level of adjacent areas
means by which ppl see, vital, but must be balanced
should be limited to 3:1 task:adj area, 5:1 task:remote dark areas, 10:1, task:remote light areas
Uniformity & Color
uniformity = perception of light being comfortable, pleasant
color = light source and incident surface interactions
Light source types
incandescent lamps
fluorescent lamps
high-intensity discharge (HID) lamps
light-emitting diodes (LED)
must balance color, cost (initial & operational), efficacy (ratio of luminous flux emitted:total power input), size, operating life, ability to control output
Incandescent lamps
tungsten filament, sealed glass bulb w/ inert/noble gas, filament glows w/ electrical current
inexpensive, compact, easy to dim, turning on/off doesn’t reduce lifespan, warm colored, lenses and reflectors easy to use
low efficacy, high heat production, short lifespan, not energy efficient
halogen lamps are incandescents (tungsten halogen lamp or quartz-halogen lamp), where filament is burned away & redeposited, burns cooler light, more uniformly, better efficacy, so, samller, longer life, but still high heat (and can explode)
reflector lamps (R lamps) & parabolic aluminized reflector lamps (PAR lamps) used metallic backing to focus beam, either flood or narrow/spot beams (most of these outlawed for inefficiency)
elliptical reflector lamps (ER lamps) are more efficient, focus, then throw light, so smaller, bc less light trapped in fixture
low-voltage miniature reflector lamps (MR lamps), small halogen lamps
Fluorescent lamps
inert/noble gas + low-pressure mercury vapor; mercury arc formed when electricity added, creates UV light, which strikes the phosphor-coated bulb, causing fluorescence
have high efficacy, low cost, long life, can be dimmed, but expensive
too UV-ish light, large, hard to control, better for general illumination, but CFLs (compact fluorescent lamps) improve this
preheat lamps: do not carry current unless in use, takes awhile to produce light
rapid-start lamps: maintain a low-voltage current so that start time reduced to ~2 seconds
instant-start lamps: maintain constant voltage
some low-efficiency fluorescent lamps outlawed, but CFL bases (not Edison screw base, but GU-24, 2-pin base) are becoming most common energy-efficient lamp base
Ballasts
device that supplies proper start/operating/control of power/voltage
magnetic: (older), lam. steel plates wrapped in copper
electronic: solid state, operate at high frequency, less noise/heat/flicker, easier to dim
multilevel: to easily change lighting levels
energy-saving: lower current, efficient ballast design
ballast factor (BF) = ratio of light output w/ particular ballast to that of a reference ballast, not used directly
ballast efficacy factor (BEF) = ballast factor x 100, used to compare same kind, number of lamps on different ballasts
power factor = how effectively a ballast converts supplied power to useable power
rated for noise (+ A-F noisy)
High Intensity Discharge (HID) Lamps
mercury vapor: electric arc passes through high-pressure mercury vapor, produces UV + visible light, phosphors can be added to warm up light
metal halide: metal halides have been added, improves color & efficacy, shortens life span (most commonly used), color shifts over life span
high & low pressure sodium: electric arc through hot sodium vapor, tube from ceramic to resist salt corrosion, very high efficacy, long life, but very yellow light, though can be color corrected; low pressure even more efficient, but deep yellow in color
all use an outer bulb to protect from UV light: clear (optical control required), phosphor coated (to warm up light), diffuse (for recessed downlights in low ceilings)
all have significant start up and cool off times
ceramic metal halide (CMH): ceramic arc tube, not quartz, burns at higher temp, better color & control, better efficacy, but expensive, hard to dim, requires a ballast
LEDs
semiconductor, solid-state electroluminescence
OLEDs: organic
PLEDs: polymer
bright, long-lived, low heat, low power consumption
low efficacy, high cost
Other lamps
neon: gas filled tubes, different colors = different gases
cold-cathode lamps: higher efficacy than neon, mostly white, larger tube
fiber optic luminaire: light conducted, often for museums, pools, near flammable storage
Articulation index
measure of speech intelligibility; words read from a preset list
low (less than .15) desired for privacy
high (above .6) for presentations
IIC
Impact Insulation Class, measures floor/ceiling assembly’s impact sound transmission
NC/NIC/NR/NRC
noise criteria: single-number ratings of acceptable background noise
noise isolation class: noise isolation class: single number rating of noise reduction
noise reduction: noise difference btwn barrier of given transmission loss
noise reduction coefficient: average sound absorption coefficient measured at fixed frequencies
Sabin formula
relates reverberation time to a room’s volume and total acoustical absorption
STC/TL
sound transmission class: average of a barrier’s ability to reduce sound (higher is better)
transmission loss: decibel difference of sound at source and sound received across barrier
Sound intensity
intensity level measured in decibels (dB) goes from 0 dB to 130 dB, threshold of hearing to painful
intensity of sound at a given point is inversely proprotional to the square of the distance from that point
Loudness
subjective, but gains of 5 dB are noticeable, 10 dB is twice as loud, 20 dB is four times as loud
decibels are logarithmic, so they don’t add up directly
use the table or:
ILtotal = IL source = 10 log n, where n is the number of noise sources
Sound transmission
thicker barriers reduce it more, less stiff barriers reduce it more (if weight is equal)
transmission loss is the difference between sound power falling on a barrier and sound power received on other side of barrier (not the same for all frequencies with one type of barrier, STC combines these)
noise reduction is difference between intensity levels in two different rooms div. by barrier, so area, and absorptive surfaces in rooms is accouted for
Noise criteria curves
depends on type of space
low frequency noises tolerated better than high
some noise required for spaces to not feel dead
preferred noise criteria is for noises that are better than acceptable
Guidelines for transmission loss
easier to block high frequency sounds
a wall w/0.1% open area will have max 30 dB transmission loss
a wall w/1.0% open are will have max 20 dB transmission loss
hairline cracks decrease transmission loss by 6 dB
a 1 sq in opening in a 100 sq ft non-absorptive wall will transmit as much sound as having no wall at all
fibrous insulation increases the STC, but the density of the insulation doesn’t matter
25 STC, normal speech can be heard
45-50 STC, only loud sounds heard faintly
Sound absorption
in free space, each doubling of distance from sound source reduces it by 6 dB, but in a room, you start to have noise reflectance
coefficient of absorption: ratio of sound intensity absorbed to the total sound receive by a surface
below 0.2 is a reflective surface, above, is absorptive, max is 1.0
NRC/noise reduction coefficient combines the coeff. abs. for different frequencies and materials (since those are all different)
NRC has been superceded by SAA/sound absorption average, which focuses on averaging only the most important frequencies
Guidelines for sound absorption
average coeff. abs. for a room should be at least 0.2
0.5 not desirable & too expensive
each doubling of coeff. abs. only reduces noise by 3 dB
if it’s going to be worth it, adding absorptive material should target a 5 dB reduction, so three times an increase from original
an increase of 10 times original is usu. the max possible
each doubling of coeff. abs. reduces reverberation times by 1/2
in large rooms, put abs. material on ceilings; in small rooms, put it on the walls
increasing abs. material will increase abs., but not very much for low frequency sounds
want a porous, interconnected web of voids for your material
Reverberation
reverb time = the time it takes for sound to be reduced by 60 dB after source has stopped
- 5-1.8-3.0 sec for music auditoriums
- 3-0.6 for small offices or broadcast studios
