Year 2 I1 Flashcards
cornea
light enters the eye through the transparent outer membrane surrounding the eye
Describe: the retina
passes through the focusing lens, and strikes the retina for form the optical image pattern
Describe: the iris
(coloured portion of the eye) acts as a diaphragm to expand or contract the pupil.
Describe the pupil
controls the amount of light that is allowed to enter the eye
List four factors affecting visibility
size
brightness
contrast
time
wavelengths of visible light
from 380 nm to 760 nm
human eye is most responsive to
555 nm or yellow-green colour range
Colour Temperature
or chromaticity is expressed in degrees Kelvin but not a measure of temperature, but rather a measurement of light quality
Low colour temp = warm colour below 3000K
High colour temp = cool colour above 4000K
Color Rendering Index (CRI) 75-100 Excellent 60-75 Good 50-60 Fair 0-50 Poor
the ability of a light source to portray the colour appearance of objects accurately
Value from 0 to 100 where 100 is the best
List 2 Light measurements
Luminous Flux quantity of light output
Luminous Flux density is the density of light flux or illumination
1 Lux
is equal to 1 lumen per square metre
Lighting equation 1
Inverse square law
E = l/d^2 E = illumination in lux l = light intensity in candela d = distance in metres
Lighting equation 2
Cosine law of incidence
E = (I/d^2) x cos(theta)
Luminous efficacy
is the ratio of the light output (lumens) to the power input (watts) Lm/W
with no losses 1 watt would produce about 683 Lumens
List three factors that affect the Quality of light
Glare
Diffusion
Colour
Two of the main causes of light loss
Lamp lumen depreciation
Luminaire dirt depreciation
Light Shapes
Straight side = S Tubular = T
Flame = F Pear-shaped = PS
Globular = G Parabolic = PAR
Standard line = A Reflector = R
Edison base
most common screw type
Tungsten-halogen lamp
also called quartz halogen or quartz iodine
compact high-intensity
white light output
Used for projection, automotive, photocopying and floodlights
contains halogen gas the aids in the regenerative cycle
Lamp life 2500-3000
operates at 5 to 6 atmospheres must be contained in case lamp shatters
Ballast function
provides the high starting voltage to ignite the tube
limits the current in the tube once the tube lights
in some short tubes only limits the current
Fluorescent lamps are measured in 8ths
T8 is 8 8ths or 1 inch in diameter
CFL
compact fluorescent lamp
can be used for replacement of a incandescent lamp
Stroboscopic effect of fluorescent lamps
makes rotating machine appear stopped
use lead-lag ballasts operating in twin-lamp fixtures
connect lamp fixtures on different phases of a three phase system
electronic ballasts eliminates this
Fluorescent lamps are classified
according to their start methods
preheat start not used much
instant-start
rapid-start
Instant start or cold-cathode starting
has a step-up transformer to a sufficient magnitude to not have to pre-heat the cathode
Slimline fluorescent is a instant-start
that has a switch incorporated in one of the lamp-holder sockets so that high voltage will not be present until lamp is fully seated
Rapid-start cct fluorescent
eliminates three major shortcomings
large, heavy ballast
high strike voltage
longer lamp life due to lower strike voltage
Electronic ballasts
take low-frequency AC convert to DC convert to very-high-frequency AC. above 20kHz
caution shock hazards high voltages can be above 347 V
the wire used for end to end fluorescent fixtures install
must be not less than 600 V rated and 90 degrees Celsius
List three types of HID lights
High-intensity discharge
Metal halide
Mercury vapour
High-pressure sodium
Describe Mercury Vapour Lamp
Must have ballast to strike small arc that vapourizes the mercury and permits striking of the main arc.
3 to 7 min starting
Restart - restrike time is 4 to 6 min
24000 hour plus operation
have a phospor coating that improves the colour by converting some UV radiation to visible light
Letter code is H for Hg
Describe Metal halide lamps
Shorter arc tube than Mercury vapour
contains additional compound metals and halogen gas that improves efficacy and colour rendition of the lamp.
first choice for good colour redition
startup is 5 to 7 min
restart and restrike can be as long as 15 min
Shorter life span 15000 hrs
letter code is MD or M
Describe High-pressure sodium lamp
HPS different in that it has no starting electrode
An arc tube that contains xenon gas and sodium-mercury amalgam
Special circuitry in the ballast provides arc strike or 2500 v or more
startup time of 3 to 4 min warm golden white
restrike time is usually less than a min
rated lifespan is 24000
can operate in any position without adverse effects on bulb
letter code is S
Letter shape codes for HID
B = bullet BT = bulged-tubular E = elliptical PAR = Parabolic aluminized reflector T = tubular
H36BT-1000/DX
H for mercury vapour 36 for ballast type BT for shape 1000 for wattage DX for colour Deluxe colour
HID Reactor ballast
only used with H and sometimes called a lag reactor ballast
works only when supply voltage is high enough to strike an arc
acts only as a choke
seldom used in new install
HID Autotransformer ballast
lag autotransfromer ballast PF .9
used with H lamps
can not be used when supply voltage varies beyond plus or minus 5%
to low or variations of voltage can keep lamp from striking
HID auto-regulator ballast
constant wattage autotransformer ballast (CWA)
With the combination of capacitor and autotransformer (reactor) give a PF .95
can handle voltage fluctuation of 40 to 50 % without extinguishing the lamp
taps for two or more supply voltages
used for all HID but most common for MH
HID regulator ballast
secondary windings are electrically isolated from the supply windings
superior to autotransformer in that it can hand plus or minus 13 % and voltage dips of up to 50 to 60%
larger and more expensive
HID HPS ballast
supplies high-voltage spike to augment the starting voltage because HPS bulb has no starting electrode.
Electronic starting aid provided pulsed voltage with a peak of 2500 to 4000V
