Lighting & Acoustics

Question 1

Definition of light

Answer 1

visually evaluable radiant energy

visible spectrum on EM radiation

Question 2

Coefficient of transmission

Answer 2

total light transmitted through a material

clear glass = 85% transmittance

translucent = transmits light, but not a clear image

Question 3

Reflectance/reflectance coefficient

Answer 3

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)

Question 4

Eye parts to process light

Answer 4

cones perceive detail and color, more near the fovea

rods perceive motion and light, surround the fovea

Question 5

Candlepower

Answer 5

unit of luminous intensity that is equal to horizontal output of a wax candle

aka candela

radiant energy output

Question 6

Illuminance

Answer 6

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

Question 7

Lumen

Answer 7

(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

Question 8

Luminance

Answer 8

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

Question 9

Luminous intensity

Answer 9

solid angular flux density in a given direction

measured in candlepower or candelas

how much radiant energy, non geometrically defined

Question 10

Illuminance targets

Answer 10

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

Question 11

Glare

Answer 11

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)

Question 12

Contrast

Answer 12

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

Question 13

Uniformity & Color

Answer 13

uniformity = perception of light being comfortable, pleasant

color = light source and incident surface interactions

Question 14

Light source types

Answer 14

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

Question 15

Incandescent lamps

Answer 15

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

Question 16

Fluorescent lamps

Answer 16

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

Question 17

Ballasts

Answer 17

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)

Question 18

High Intensity Discharge (HID) Lamps

Answer 18

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

Question 19

LEDs

Answer 19

semiconductor, solid-state electroluminescence

OLEDs: organic

PLEDs: polymer

bright, long-lived, low heat, low power consumption

low efficacy, high cost

Question 20

Other lamps

Answer 20

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

Question 21

Articulation index

Answer 21

measure of speech intelligibility; words read from a preset list

low (less than .15) desired for privacy

high (above .6) for presentations

Question 22

IIC

Answer 22

Impact Insulation Class, measures floor/ceiling assembly’s impact sound transmission

Question 23

NC/NIC/NR/NRC

Answer 23

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

Question 24

Sabin formula

Answer 24

relates reverberation time to a room’s volume and total acoustical absorption

Question 25

STC/TL

Answer 25

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

Question 26

Sound intensity

Answer 26

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

Question 27

Loudness

Answer 27

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

Question 28

Sound transmission

Answer 28

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

Question 29

Noise criteria curves

Answer 29

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

Question 30

Guidelines for transmission loss

Answer 30

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

Question 31

Sound absorption

Answer 31

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

Question 32

Guidelines for sound absorption

Answer 32

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

Question 33

Reverberation

Answer 33

reverb time = the time it takes for sound to be reduced by 60 dB after source has stopped

1. 5-1.8-3.0 sec for music auditoriums
2. 3-0.6 for small offices or broadcast studios