Producing Visible Light
Reading Preview
Key Conc:ept
• wtwl Me .he dif/efenl t)'IM'" of
light bulbol
Key Terms
~ Discover Activity
How Do Light Bulbs Differ? "
B
1. Your te<><::her will give you one illCalldescent ..1Id one
fluoreKent Ughl bulb.
2. EL'lmine the bulbs. RecOfd your obwrvallons and deso;ribe any
• IIlumin.lled
• lumll'lClU\
diffef('llCa. Draw each type of bulb.
• '!>K1I<K<0V"
3. How do you think ei><h bUlb produc.... light1
• incandt.>5<:enl light
• h.nglotefl.lwlogen bulb
• fIuo<8unilight
Think It Over
Posing Que.tions Make I lin of five QlIe'Stloos you could
hetp you underuand how each bulb WOfb.
a~
to
• Yapo< l;ghl
• neon I;ghl
Target Reading Skill
Comparlng and Conu'utl"'ll
Compare and contra$! lhe l"'e
trP'" of light bulbi by wmpleting
a t.1~ lib ,he one below.
_
...
.
...-- ,." '-­
Uvhll\llbl
H" 9 n
....Ie<ial
""""'"
Look around you. MOSI of the objects you Set: arc visible
be<ause they rdkcl light from 500lC kind of light source. An
obje<:t is illuminated if you ~e il by rcftcrte<! light. The page
you are reading, }'OUr desk, and lhe moon arc examl>les of illu­
minated objecls. An objcct is luminous if it gives off ils own
light. A light bulb, a burning log. and lhe sun all arc examples
of luminous objects.
Different types of light bulbs may be used to illuminate the
spaces around you. Common types of light bulbs include
incandescent, lungslen-halogen. f1l1Oresant, \llpor. and noon
lights. Some light bulbs produce a continuous spectrum of all of
the wavekngtlu of yisible light. Others produce onlr a few \Yaw­
lengths. YOlll.'<In use an instrument called a spectroscope to view
the different colors of light produced by a light bulb.
Incandescent Lights
Have }"ou heard the phrase ~red hot~? When a glassblo.....er
heats glass. il glo~ and gives off red light. At a higher tem­
perature. it gi\"eS off wrute light and the glass is said to be
·white hot.~ An incandescent light (in kun DES unt) is a
light bulb lhat glows when a ftlarnenl inside it geu while
hoi. Thomas Edison, the Ameriam inventor, patemcd the
first practical in<andcscent light bulb in 1879.
... .
.. GIa..blo_r wo"ing
with hut..:! gla..
...... ,
Incandescent Ughts
Tungsten
filamerll
Glass bulb-­
A filament glows when elecui< ClImmt pas~
through it. Comparlnl) and Contra.ting How
are ordinary light bulbs liie tungsten-ha/oqffi
bulbs? How a,e they diffe,enrl
Bulb made from
• INt~ial ulled
,..m
-
Tungmm
filament
Nitrogen 9"1
and argon gas
inside bulb
nl--T~eof
hc>1ogen gas
Inside bulb
Ordinary Light Bulb
Ordinary Light Bulbs Look closely a\ the ordinary light
bulb shown in Figure 9. Notice the thin wire called the fila­
menl. It is made of a metal (ailed tungsten. When an el«tri<:
current passes through the filament, il quickly heals up and
becomes hot, giving off white light. The filament is enclosed in
an airtight glass bulb. Most ordinary light bulbs contain small
amounts of nitrogen and argon gases.
Ordinary light bulbs are nOi effidenl. 1..tSS than 10 percent
oflheirmergy is gi\'cn off as light. Most of their energy isgivrn
off as infTllred rays. That's why they get so hoI.
Tungsten.Halogen Bulbs A bulb lhal has a tungsten fila­
ment and contains a halogen gas soch as iodine or bromine is
Ollled a tungstnl-balogen bulb. The filamenl nf this bulb gcts
much hOller than in an ordinary light bulb, so the hulb looks
whiter.
Tungsten-halogen bulbs are more efficient than ordinary
bulbs because they give off more light and use less clectrical
energy. But they also give off more heat. Because tungsten­
halogen bulbs get so hoI, they most be kept away from materi­
als thaI could calch fire.
§4~;t. 'I) What gases are uHod
in
tungsten-h&logen bulbs?
Observing
UM! a l.peCtroscop.e to view
light from two l.OUrccs.
CAUTION: Do not view the
sun with the spKtroKope.
•
1. took through the
s.pecIroscope at an
ordinasy light bulb. Ul.e
colored pencils to draw
and tabel what you see.
2. Now, look at a floofesceot
light through the
spectroscope. A.galn, df_
and label what you see.
How are the colon you see
the same? How are they
diffeflmt?
Chapter 3
o. 8S
FlGUIlf 10
fluol'fl~nt Ught
A fIUQrl!'$«'nt tight
i5 cool becallW W!ry linl"
"nt!rgy Is glW!fl off III infrared
fll),!,. Inferring Why is It
fWorIeK..nt light .. fficiMl1
Gt.ss tube
__"''''''''''';;'''':.;:n;urynpor
.
t~
Other Light Sources
[ncand~l light bulb~ are not the only light bulm. )'Ou ~
around you. Some spa<es arc lit by fluorescent lights. Str«ts
anu parking lots may bt' lit with vapor lights. Noon lights are
often used to altract attention to stura and theat('rs.
."..",
Sodium Vapor Llghts
SOdium vapor lights giW! off
a yellowish light.
FluOnIscent Lights lhl'e )'tIu ewr nOliced long, narrow
glass lUbes lhat illuminate schools and stores? These are fluo­
rescent light bulbs. It f1uoresnntlight (floo IIfS unt) is a bulb
Ihal conlaim a gas anl.! is coated on the inside with a powder.
When an electric current P.1SSl.'S through the bulb, it causes the
gas inside to give of( ultraviolet rays. When the ultraviolct rays
hit the powder in the lUbe, the po....'<ier girl'S of( visible light.
Fluorescent lights gil't' off most or Iheir energy as visible
light and only a little energy as inrnred rays. Thcrc(ore, fluo­
rescent lights do not get as hot as incandescent light bulbs.
'Iney also usually lasl longer than incandescent lights and use
less electrical ellergy for the same brightness. So. fluorC$Cent
Iights are \'t'ry efficient.
Vapor Lights A bulb that contains nl'{ln or argon gas and a
small amount or solid sodium or mercury is a vapor light.
When an electric current passes through the gas, the gas heats
up.1bc hot gas then heats the sodium or mercury. The heating
causes the sodium or mercury 10 change rrom a solid into a gllS.
In a sodium \'3por light, the particles or sodium gas glow to
give off a yellowish light. A mercury val)Or light produces a
bluish light.
Both sodium and men:ury V'Jpor lights are used ror street
lighling and parking loIs.. 1bcy require: very little ele<:lrical energy
to gi\'C off a great deal of light, so they are quite efficient.
86.0
Neon Ughtt A noon lighl is a sealed glass lube thai coo­
lains noon gas. When an dearie current pa-'i.~ Ihmugh lhe
neotl. particles of Iht gas absorb mtfgy. Hownocr, Inc ps
particles C1nnal hold ItIt mtrgy for V\"ry long. The enagy is
rekaKd in the fO£m of light. This procu.s is ClUed deCIric
discharge through ~
A Irue neon light ghu off red light. as
in
Figure 12. BUI often, lights lbal COOlain diffnm.1 ~ or a
mixture of pK$ are also called neon lights. Differenl gases
produce differenl colors of light. f"Of aJ.mpk. both aTln
gas and mercury vapor produee greenish-blue lighl. Hdium
gilU pinllighL Krypton gives a pal.! viokllighl. Sometimes
cokJred glass lUbes arc used 10 produee other roIon. Noon
lights are commonly UKd for brighl. Ruby signs.
..........
..... n
The (olor of a _light depellds
~ on ....t'>idI g.as or ~ _
in the tublo..
in
mown
" ' . ; WhIot (oklr of light doH a neon light t1vt! off?
",,'l{IIHl
3 Assessment
"@Target Reading Skill Comparing and Cont'il'Sti"ll Use
!he information in your taille about light bulbs 10 help
you aru;"TI Quesl.ion I below.
Reviewing Key COf!cepts
1. a. Uliting What are fi\'e common t)'pc$ ofl~hl bulbsf
b. Explaining How do inundescenllighl bulbs wurlt?
L Inferring Lamps Ihal use ordinary light bulbs oflen
have doth or p;lpn shadn. But tun~ten~haIogen
lamps usually haw metal shadel. E>;plain.
d. Making Generalizations Whal gi\U olTlight in
iOOlndescentlighl bul!».! \\!hal gi\"" off light in
other types of light bulbs?
At HUfll!' Activity
Buying Ught Bulin InVite f~ilv
members to visit. Mrdw,)re store.
Ask a salespei'1Of'l to desc,ibe the
diffe,ent kinds of light bulbs
avail.ble. Read the infoflnation
about el<h bulb on the packages.
Looli; for the (ost and the expected
life of the bulbs. How does this
information help ylXl and)'OYr
family to choose bulbs lor different
purposes?
Chllpt•• )
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