Compact, energy-saving lamp

Details Compact, energy-saving lamp Compact, energy-saving lamp

1999-10-14

2002-12-03

Patel, Nimeshkumar D. (Department: 2879)

Electric lamp and discharge devices

With luminescent solid or liquid material

With gaseous discharge medium

C313S483000, C313S485000, C313S639000, C313S640000, C252S30140R

Reexamination Certificate

active

06489716

ABSTRACT:

The invention relates to a compact energy saving lamp which is distinguished by high luminous flux and very good color rendering characteristics in conjunction with long life. The field of application is that of mercury vapor low-pressure discharge lamps in lighting and illumination technology.
Fluorescent lamps in general, when a suitable excited gas is discharged involving suitable phosphors, generate visible light for illumination purposes.
Particularly widely used for interior lighting are compact mercury vapor low-pressure discharge lamps, comprising a glass bulb which is fabricated so as to be vacuum-tight and is filled with mercury and noble gas and on its inside is provided with a phosphor layer which converts the shortwave mercury resonance radiation having energies of about 6.71 eV and 4.88 eV into visible light.
Conventional compact energy saving lamps have lives of about 8,000 hours and, depending on output, type and color temperature, have a luminous flux of between about 250 lm and 4,300 lm.
The energy saving lamp operating in accordance with the three-band principle comprises the blue mercury resonance radiation and also a green component, which is particularly important for light output ratio and luminous flux, and in addition the phosphor Eu-activated yttrium oxide (YOX) as the red component and, in lamps of elevated color temperature, the phosphor Eu-activated aluminate such as, for example, BAM and/or SAE as an additional broadband blue component.
In fluorescent lamps, in particular compact lamps but also three-band fluorescent lamps, preferential use is made, as green components, of compounds which, owing to their typical terbium emission, are narrowerband emitters with a maximum wavelength of about 541-543 nm. These include the phosphors cerium magnesium aluminate: Tb (CAT) as claimed in AT 351 635, lanthanum phosphate: Ce, Tb (LAP) as claimed in DE 33 26 921 and U.S. Pat. No. 4,891,550, and lanthanum phosphate silicate: Ce, Tb (LAPS) as claimed in DE 32 48 809 and Y
2
SiO
5
: Ce, Tb as claimed in EP 037 688 as the most important representatives. All these phosphors are distinguished by high temperature stability and light output ratio. Drawbacks of these compounds are the high costs, caused by the preparation temperatures required of 1300° C. to 1600° C. Moreover, the stability of the phosphors overall is too low with respect to the discharge when the fluorescent lamp is lit, thus limiting the useful life of the latter to about 8,000 hours.
EP 023 068 describes a fluorescent lamp which employs the phosphor gadolinium magnesium pentaborate: Ce, Tb (CBT) having an emission maximum at 542 nm. In addition to comparably good emission characteristics, this phosphor has a higher stability compared with the phosphors CAT and LAP.
Catalogs of various fluorescent lamp manufacturers disclose that in the case of compact energy saving lamps it is possible, as shown by the following table,
Lamp
number
Output/W
Luminous flux/Im
Color temperature/K
Ra (8)
1
9-23
600-1500
2700-5600
80
2
15-23 
925-1580
3000
82
3
5-50
250-4300
2700-5000
82
4
5-20
250-1200
2700-6000
82
5
5-20
250-4000
2700-8500
82
6
18-32 
1250-2200 
2700
82
7
5-54
250-3200
2700-4100
80
to employ conventional phosphors in achieving quite different light colors in conjunction with a color rendering index of Ra(8)=80 to 82. The life as specified is generally about 8,000 hours.
Catalogs of leading lamp manufacturers also disclose that in the case of linear fluorescent lamps it is possible to achieve extended useful lives by means of protective layers. A known method for this is to coat the glass bulb by decomposing gaseous compounds or by applying a slurry in the form of a suspension comprising the protective agent. This phosphor-containing layer is generally applied on top of the protective layer. DE 3 322 390, however, also describes a method in which, conversely, an aluminum protective layer covers the phosphor layer applied to the lamp bulb, said protective layer being applied in the conventional manner, and similarly to the phosphor-containing layer, by means of a water-soluble suspension. A method for treating the glass surface by ion exchange and sealing by means of the protective layer is described in DE 3 023 397. Further examples are listed in U.S. Pat. No. 4,923,425 and U.S. Pat. No. 4,344,016. EP 0 762 479 describes a lamp in which the protective layer is achieved by hydrolysis of organometallic compounds which are admixed to the phosphor-containing suspension. In DE 3 322 390 a rare earth oxide layer in the nanometer range is prepared by flushing the lamp bulb with a suitable organometallic solution, followed by a sintering process.
Color rendering with the standard compact lamps known hitherto does not or not significantly exceed the Ra(8) value of 82 and is therefore classified as color rendering class IB.
EP 0 550 937 A2 disclosed a mercury vapor low-pressure discharge lamp having color rendering glass IA. This includes lamps having a higher wall load of E(UV)>500 W/m
2
. The color point (x, y) is located on or near the Planck curve, and the efficiency of the luminescence is comparatively high. Still, it is about 25 to 30 percent or even more below the efficiency of comparable standard compact lamps. The phosphor layer used in the lamp as claimed in EP 0 550 937 comprises three phosphors. The first is a blue-emitting phosphor activated with bivalent europium. The second phosphor is activated with bivalent manganese and has at least one emission band in the red spectral region. The third phosphor, which has its main emission in the yellow spectral region, is a (strontium, barium, calcium) orthosilicate activated with bivalent europium.
In the mercury vapor low-pressure discharge lamp as claimed in EP 0 596 548 A1, five luminescent materials are used as a phosphor, in order to achieve very good color rendering in conjunction with low aging of the lamp. The reduction in luminous flow of such deluxe lamps does, however, amount to more than 30 percent compared with standard compact lamps.
It is an object of the invention to improve the quality of use of the compact energy saving lamp, the aim being to achieve a high initial luminous flux and improved color rendering characteristics in conjunction with long life.
This object is achieved by the compact energy saving lamp having a very similar color temperature of between 2300 K and 6500 K comprising a discharge vessel which is fabricated so as to be vacuum-tight, which is filled with mercury and noble gas and on whose inner wall side the luminescent layer is disposed on top of an interlayer comprising silicon and/or aluminum and/or boron, and means for maintaining the discharge, the power density of the power absorbed by the column relative to the luminescent layer preferably being greater than 500 W/m
2
and the UV radiation predominantly having energies greater than 3.5 eV, is to fabricate, wherein the luminescent layer comprises at least two phosphors. According to the invention, the luminescent layer comprises as a first phosphor a green-emitting gadolinium magnesium borate silicate, activated with cerium and terbium (BSCT) having the composition
(Y,La)
1−x−y
Ce
x
Gd
y−z
Tb
z
(Mg, Zn, Cd)
1−p
Mn
p
B
5−q−s
(Al, Ga, In)
q
(X)
s
O
10
,
where X=Si, Ge, P, Zr, V, Nb, Ta, W or the sum of a plurality of the elements listed
and it is further the case that
p=0 and z≠0,
0.01
≦x
≦1
−y−z
0
≦y
≦0.98
y+z
≦0.99
0.01
≦z
≦0.75
0
≦q
≦1.0
0
≦s
≦1.0
and as a second phosphor, emitting in the red spectral region, preferably comprises yttrium oxide:Eu
3+
which has the formula Y
2−x
Eu
x
O
3
, where 0.01<x<0.2.
Table 1 shows a few examples of such improved warm-hue compact lamps embodied as a high-standard compact lamp within the tolerance ellipse.
TABLE 1
CL
Relative luminous
Color
x,y coordinates
number
flux
temperature/K
x
y
Ra(8)
1
104
2682
0.4667
0.4207
84
2
104
2704
0.4650
0.4205
84
3
105
2727
0.4633
0.4204
84
4
106
274

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