Note: Descriptions are shown in the official language in which they were submitted.
3 ~ 8 5
RDnO22'101
ELE~TRODELE~S FLUORE~GENT LAMP
CONFIGURATI~~
Field of the Inven~Qn
The present invention relates generally
to fluorescent lamps and, more particularly, to a
high-efficacy electrodeless fluorescent lamp
including an envelope configured to have a height-
to-width rati~ of less than one.
Fluorescent lamps generally require lower
electrical power to operate than conventional
incandescent lamps and are generally more efficient
than incandescent lamps on a lumens per Watt basis.
Some fluorescent lamps have therefore been designed
to replace incandescent lamps in standard fixtures.
However, the use of fluorescent lamps as
-incandescent lamp replacements is limited by the
fact that practical fluorescent lamps are generally
larger (i.e., longer) than incandescent lamps which
produce the same light output.
As a class, electrodeless fluorescent
lamps are generally smaller, i.e., shorter, than
conventional fluorescent lamps, but are still not
as short as desired. Typical electrodeless
fluorescent lamps use an envelope with a height
greater than or equal to the width. Many envelopes
are spherical. By way of illustration, exemplary
2~ 039~5
RD0022 1C1
electrodeless fluorescent lamp configurations are
shown in: commonly assigned U.S. Pat. No.
4,017,764 of J.M. Anderson; commonly assigned U.S.
Pat. No. 4,187,447 of V.M. Stout and J.M. Anderson;
and in the advertising brochure distributed by
Philips Lighting at the Hanover Fair in April 1991.
For fluorescent lamps in general, there
is a well-known trade-off in size versus lamp
efficacy. That is, for a given light output,
efficacy decreases as lamp size decreases. The
reason is that discharge current density and
electron density, and hence discharge loss
mechanisms, increase as a result of a smaller
discharge space.
Accordingly, it is desirable to reduce
the size ~more specifically, the height) of an
electrodeless fluorescent lamp without sacrificing
efficacy.
Summ~y of the lnvention
An electrodeless fluorescent lamp has an
envelope configured to have a height-to-width ratio
of less than one. According to one embodiment, the
envelope is ellipsoidal. Advantageously,
electrodeless fluorescent lamps configured in
accordance herewith operate at higher efficacies
than incandescent lamps and are useful for
replacing such lamps in standard fixtures.
21~398~
~D0~2101
e Drawi~
The features and advantages of the
present invention will become apparent from the
following detailed description o~ the invention
when read with the accompanying drawings in which:
Figure l is a partial sectional view of
an electrodeless fluorescent lamp envelope of the
prior art;
Figure 2 is a partial sectional view of
an electrodeless fluorescent lamp envelope of the
present invention; and
Figure 3 is a graphical comparison of
lS average arc e~ficacy for standard spherical
electrodeless fluorescent lamp envelopes and
electrodeless fluorescent lamp envelopes according
to the present invention, each lamp envelope having
the same diameter.
~etailed ~escriptiQn of the I~vention
Figure l illustrates a typical
electrodeless fluorescent lamp lO having a
spherical bulb or envelope 12 containing an
ionizable gaseous fill. A suitable fill, for
example, comprises a mixture of a rare gas (e.g.,
krypton and/or argon) and mercury vapor and/or
cadmium vapor. An induction transformer core 19
having a winding 16 thereon is situated within a
-, 'i , -. :. , .: . ':. : 1:, ':',: ' ,~ , . , ': , ' ' . , '
.
2103985
RD00221 01
q
re-entrant cavity within envelope 12. (However, i~
is to be understood that some fluorescent lamps do
not employ a transformer core, and the principles
of the invention apply equally to such lamps.) The
interior surfaces of envelope 12 are coated in
well-known fashion with a suitable phosphor which
is stimulated to emit visible radiation upon
absorption of ultraviolet radiation. Envelope 12
fits into one end of a base assembly (not shown)
containing a radio frequency power supply with a
standard incandescent lamp base at the other end.
In operation, current flows through
winding 16, establishing a radio frequency magnetic
field in transformer core 14. The magnetic field
within transformer core 14 induces an electric
field within envelope 12 which ionizes and excites
the gas contained therein, resulting in an
discharge 18. Ultraviolet radiation from discharge
18 is absorbed by the phosphor coating on the
interior surface of the envelope, thereby
stimulating the emission of visible radiation by
the lamp envelope.
Disadvantageously, for a lamp with a
spherical envelope such as that shown in Figure 1,
there is a trade-off between height versus lamp
efficacy. That is, for a lamp having a spherical
; envelope, to decrease the envelope height, the
diameter of the envelope must be decreased, leading
to lower efficacy. For example, an electrodeless
,
:
: . . .- . -, .. .. . .. ....... , ~. ,.. ,,,; , .,"",",, , ,.,, . ,,,.. ,;~ .", "., , . ", "
: ~ : : .: : - :: . : :,:: . ., ., ,.,. ~,, ,, ,:; .. :: . ,, .: . ...
' ':: ,i ;J. ~ '';!; :.. .
' ,-.' : '' ' ':' . '. , . ~ ;, :, , . ' . . ':; ' ''j:'~:, ':', ': ,' ::: : ':.,: '' ' ' '. : ' ' ' ;!: ' '` ' ,
: ' ' ' ' : , :: : . , " . . : ! ,. : . ; . .: . . . , :;: . . . : : . . . , ~ . . . .
21~3~85
- ~D0022101
-- 5 --
lamp having a sphe-ical envelope with a 68 mm
diameter and producing 1300 lumens is known to have
a lower efficacy than a lamp constructed with a
spherical envelope with 80 mm diameter also
producing 1300 lumens.
In accordance with the present invention,
Figure 2 illustrates an electrodeless fluorescent
lamp 20 having an envelope with a height-to-width
ratio of less than one. Since the top and bottom
portions of the envelope have very low discharge
density, these portions of the envelope can be
substantially reduced in size according to the
present invention without creating the increase in
current density that would otherwise decrease the
lamp efficacy. In particular, the fluorescent lamp
of Figure 2 comprises an envelope 22 having an
ellipsoidal (or "flattened spherical") shape.
preferred height-to-width ratio is in the range
from approximately 0.5 to approximately 0.9.
Advantageously, the shortened configuration of such
fluorescent lamps, without sacrificing efficacy,
render them as desirable replacements for
incandescent lamps in standard base assemblies.
~x~mple
Two spherical electrodeless fluorescent ^~
lamp envelopes, each having an outer diameter of 80
mm, and two ellipsoidal electrodeless fluorescent
lamp envelopes, each being 80 mm high by 70 mm
wide, were constructed. Each lamp envelope was
; ` ;~
21~3~5
~0v22~D1
-- 6 --
dosed with mercury and 0.5 Torr of krypton; and was
operated with an air core transformer. At five arc
power levels, from 15 Watts to 35 Watts, each lamp
envelope was allowed to warm up through its optimum
mercury temperature. Peak lumen output and power
output were measured at each arc power level, and
peak efficacy was measured. A graph of average
peak efficacy versus arc power for each pair of
lamp envelopes is illustrated in Figure 3, the
solid line representing average efficacy of the
standard spherical lamp envelopes and the dashed
line representing average efficacy of the
ellipsoidal lamp envelopes.
Advantageously, as indicated by the data
of Figure 3, the efficacy of an electrodeless
fluorescent lamp is not sacrificed (and may even be
improved) by configuring the lamp envelope
according to the present invention, resulting in a
small, high-efficacy replacement for incandescent
lamps in standard fixtures. Specifically, lamp
efficacy is not sacrificed by the shortened
envelope configuration because current density is
not increased.
While the preferred embodiments of the
present invention have been shown and described
herein, it will be obvious that such embodiments
are provided by way of example only. Numerous
variations, changes and substitutions will occur to
those of skill in the art without departing from
,~ .
2~3~8~
RD0022101
-- 7
the invention herein. Accordingly, it is intended
that the invention be limited only by the spirit
and scope of the appended olaims.
.- . . ~.: .. , , . : ,~ ,. ., .... : ,, :, ,.. ;. : .
, , . . ~ ~ ' , : ' . .: ! : ' , : '
