United States Patent
`van Kemenade et al.
`
`[19]
`
`[11] Patent Number:
`
`4,727,283
`
`[45] Date of Patent:
`
`Feb. 23, 1988
`
`[54] LOW-PRESSURE MERCURY VAPOUR
`DISCHARGE LAMP
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`[75]
`
`Inventors:
`
`Johannes T. C. van Kemenade;
`Gerardus H. M. Siebers; Jean J.
`Heuvelmans; Johannes T. W. deHair,
`all of Eindhoven; Johannes W. ter
`Vrugt, Geldrop, all of Netherlands
`
`[73] Assignee: U.S. Philips Corporation, New York,
`NY.
`
`[21] Appl. No.: 883,186
`
`[22] Filed:
`
`Jul. 8, 1986
`
`Foreign Application Priority Data
`[30]
`Jul. 15, 1985 [NL] Netherlands ......................... 8502025
`
`Int. Cl.4 .............................................. H01J 61/46
`[51]
`
`[52] US. Cl. ...................
`313/487; 252/301.4 R
`[58] Field of Search ................ 252/301.4 R, 582, 584,
`252/586, 301.4 P; 313/483, 486, 487, 485;
`315/57
`
`2/1976 Verstegen et al.
`.................. 313/487
`3,937,998
`
`5/1977 Schuil ....................... 252/301.4 R
`4,024,070
`..................... 313/485
`4,177,401 12/1979 Yamane et a1.
`2/1982 Barnes ...................... 252/301.4 R
`4,314,910
`
`.......... 315/57
`4,383,200
`5/1983 Van 2011 et a1.
`
`4,447,756
`5/1984 Kohmoto et a1.
`313/487
`
`......
`4,559,470 12/1985 Murakami et a1.
`313/485
`
`Primary Examiner—David K. Moore
`Assistant Examiner—Mark R. Powell
`Attorney. Agent, or Firm—John C. Fox
`
`[57]
`
`ABSTRACT
`
`'A low-pressure mercury vapor discharge lamp with a
`luminescent layer whose emission mainly lies in three
`spectral ranges and whose loading amounts to at least
`500 W per at2 surface area of the luminescent layer, is
`characterized by having an absorption layer of a lumi-
`nescent aluminate activated by trivalent cerium and
`having a garnet crystal structure. The absorption layer
`permits the obtaining of low color temperatures (down
`to 2000 K.).
`
`18 Claims, 2 Drawing Figures
`
`
`
`TCL 1029, Page 1
`TCL 1029, Page 1
`
`

`

`US. Patent
`
`Feb. 23, 1988
`
`
`
`
`
`
`
`
`’é/II/Il/mlI?__________.__.
`
`
`/////
`
`TCL 1029, Page 2
`TCL 1029, Page 2
`
`
`

`

`1
`
`4,727,283
`
`LOW-PRESSURE MERCURY VAPOUR
`DISCHARGE LAMP
`
`BACKGROUND OF THE INVENTION
`
`5
`
`20
`
`10
`
`15
`
`The invention relates to a low-pressure mercury va-
`pour discharge lamp, whose emission mainly lies in
`three spectral ranges and of which the colour tempera-
`ture of the emitted light lies in the range of 2000—3000
`K., this lamp being provided with a gas-tight discharge
`envelope transparent to radiation and having a gas fill-
`ing comprising mercury and a rare gas and with a lumi-
`nescent layer comprising luminescent materials whose
`emission mainly lies in the range of 590—630 nm and in
`the range of 520—565 nm, whilst further means are pro-
`vided for maintaining a column discharge in the gas
`filling, the power consumed by the column being at
`least 500 W/m2 surface area of the luminescent layer.
`Low-pressure mercury vapour discharge lamps,
`whose emission mainly lies in three spectral ranges, also
`designated as three-band fluorescent lamps, are known
`from US. Pat. No. 4,176,294 and from Netherlands
`Patent Specification No. 164,697. These lamps are com-
`monly used in general illumination and have the advan- 25
`tage that they have both a good general colour rendi-
`tion (colour rendition index R(a, 8) of at least 80) and a
`high luminous efficacy (up to values of 90 lm/W and
`higher). This is possible because the emission of these
`lamps is mainly concentrated in three comparatively 30
`narrow spectral bands. For this purpose the lamps con-
`tain a red luminescing material whose emission mainly
`lies in the range of 590—630 nm and a green luminescing
`material whose emission mainly lies in the range of
`520—565 nm. The required emission in the third spectral 35
`range, i.e. the range of 430—490 nm, is supplied in many
`cases by a blue luminescing material. However,, the
`visible radiation emitted by the mercury vapour dis-
`charge itself also provides a contribution (i.e. the emis-
`sion of the 436 nm mercury line) in this spectral range.
`The lamps emit white light at a given colour tempera-
`ture, that is to say that the colour point (x,y in the CIE
`colour coordinate diagram) of the emitted radiation lies
`on or near the line of the black body radiators. The
`colour point of fluorescent lamps of low colour temper- 45
`ature is generally chosen to lie preferably slightly above
`(for example about 0.010 in y coordinate) the line of the
`black body radiators.
`A desired colour temperature of the light emitted by
`a three-band fluorescent lamp is obtained by a suitable so
`adjustment of relative contributions in the three spectral
`ranges to the overall emission of the lamp. As the colour
`temperature of the lamp is lower, the contribution in the
`blue range of 430490 nm should be smaller. It follows
`from the aforementioned Netherlands Patent Specifica- 55
`tion No. 164,697 that the minimum attainable colour
`temperature for lamps having an inner diameter of the
`tubular discharge envelope of about 36 mm is about
`2300 K., in which event the lamp need no longer con-
`tain a blue luminescing material and all the required 60
`radiation in the blue spectral range originates frOm the
`blue mercury radiation. In lamps having a smaller inner
`diameter of the discharge envelope, especially a diame-
`ter of about 24 mm, the mercury vapour discharge is
`found to be more efficient the relative contribution of 65
`the blue mercury line being larger. Consequently for
`these lamps. the minimum attainable colour temperature
`is found to have a higher value, i.e. about 2500 K.
`
`2
`Three-band fluorescent lamps of the kind mentioned
`in the opening paragraph are known, for example, from
`us. Pat. Nos. 4,335,330; 4,199,708; and 4,374,340, and
`are generally of very compact construction and in-
`tended to replace incandescent
`lamps. Due to their
`compact construction, the luminescent layer in these
`lamps is heavily loaded, that is to say, the power con-
`sumed by the column during operation of the lamp is at
`least 500 W per m2 of surface area of the luminescent
`layer. This is considerably higher than the load of the
`luminescent lamp layer in the aforementioned lamps
`having an inner diameter of about 36 and 24 mm, re-
`spectively, which load has a value of the order of 300
`and 400 W/mz, respectively. It has been found that in
`these heavily loaded lamps the relative contribution of
`the blue mercury radiation is even higher, and that such
`lamps without a blue luminescing material have a col-
`our temperature of the emitted light of at least about
`2700 K. at colour points lying on the line of the black
`body radiators. As a result of this, and also of their high
`R(a, 8), these lamps are suitable to replace incandescent
`lamps.
`Hitherto, incandescent lamps have been mainly used
`for interior illumination. With a view to saving energy,
`it is often desirable to replace incandescent lamps with
`fluorescent lamps. A typical value of the colour temper-
`ature of an incandescent lamp is 2650 K. However, the
`use of colour lamps (for example the so-called fiame
`lamps) and dimmers in interior illumination result in
`colour temperatures down to about 2000 K. A disad-
`vantage of the aforementioned heavily loaded fluores-
`cent lamps is that due to the intense blue mercury radia-
`tion they cannot be used in the frequently desired col-
`our temperature range of about 2000 to about 2700 K.
`The invention has for its object to obviate the said
`disadvantage and in general to provide means for shift-
`ing the colour point of heavily loaded three~band fluo-
`rescent lamps and for reducing the colour temperature,
`while substantially maintaining the good general colour
`rendition and the high relative luminous flux.
`
`SUMMARY OF THE INVENTION
`
`A low-pressure mercury vapour discharge lamp of
`the kind described in the opening paragraph is charac-
`terized according to the invention in that the lamp is
`provided with an absorption layer comprising an alumi-
`nate activated by trivalent cerium and having a garnet
`crystal structure.
`The said garnet is a known luminescent material (See
`for example J.O.S.A., 59, No. l, 60, 1969), which ab-
`sorbs short-wave ultraviolet radiation, but especially
`absorbs radiation having a wavelength between about
`400 and 480 nm and converts it into radiation in a wide
`emission band (half-value width of about 110 nm) with
`a maximum at about 560 nm. It has been found that the
`use of such a luminescent garnet in an absorption layer
`for three-band fluorescent lamps leads to a shift of the
`colour point of the radiation emitted by the lamp and
`allows for a reduction of the colour temperature of the
`lamp.
`A reduction of the colour temperature in itself could
`be attained with any yellow pigment absorbing blue
`radiation. However, a yellow pigment leads to a reduc-
`tion (unacceptable for this lamp type) of the relative
`luminous flux so that it cannot be used.
`
`_
`
`The use of the luminescent garnet in lamps according
`to the invention has the advantage that the absorbed
`radiation is no lost, but is converted with a high effi-
`
`TCL 1029, Page 3
`TCL 1029, Page 3
`
`

`

`3
`ciency into visible radiation so that high relative lumi-
`nous fluxes are obtained. In addition, the lamps accord-
`ing to the invention have high values of R(a, 8), which
`could not be expected because it is known for three
`band fluorescent lamps that radiation in the range of 5
`565-590 nm, in which a comparatively large part of the
`emission of the garnet is found,
`is detrimental to the
`colour rendition properties.
`A preferred lamp according to the invention is char-
`acterized in that the luminescent aluminate having a
`garnet structure corresponds to the formula Ln3.xCex.
`A15.p.anpSc9012, in which Ln is at least one of the
`elements yttrium, gadolinium, lanthanum and lutetium
`and in which
`0.01 éxé 0.15
`
`10
`
`15
`
`20
`
`0§pé3 and
`Oéq § 1.
`in the
`As appears from the formula and conditions,
`garnet one or more of the elements Y, Gd, La and Lu
`may be used as the cation Ln and the aluminium may be
`partly replaced within the aforementioned limits by
`gallium and/or scandium. The Ce activator replaces
`part of the Ln and is present in a concentration x of 0.01
`to 0.15. Ce contents lower than 0.01 lead to materials 25
`having an insufficient blue absorption, while for Ce
`contents higher than 0.15 the garnet is formed insuffi-
`ciently and undesired subphases may be obtained.
`Preferably, such a lamp according to the invention is
`characterized in that in the garnet Ln is yttrium and in
`that the garnet does not contain Ga and Sc(p=q=0).
`Such materials in fact have the most favourable absorp-
`tion properties and supply the highest luminous fluxes.
`In an embodiment of a lamp according to the inven-
`tion, the absorption layer is disposed on the outer sur— 35
`face of the discharge envelope. This has the advantage
`that the mercury resonance radiation produced in the
`lamp is utilized to the optimum and the absorption layer
`only absorbs the undesired blue radiation and converts
`it into visible radiation. In general, such a lamp will be
`provided with protection, for example an outer bulb, or
`will be used in a closed luminaire.
`
`30
`
`40
`
`45
`
`Another embodiment of a lamp according to the
`invention is characterized in that the absorption layer is
`disposed on the inner surface of the discharge envelope
`and in that the luminescent layer is disposed on the side
`of the absorption layer facing the discharge. In this
`lamp, the mercury resonance radiation will mainly be '
`absorbed by the luminescent layer. The use of an outer
`50
`bulb or a closed luminaire is not necessary for this lamp.
`Another embodiment of a lamp according to the
`invention is characterized in that the garnet activated
`by trivalent cerium is mixed with the luminescent mate-
`rials of the luminescent layer so that the luminescent 55
`layer is at the same time the absorption layer. Such a
`lamp can in fact be manufactured in a simple manner
`because the absorption layer and the luminescent layer
`can be introduced into the lamp in a single operation.
`In a particularly advantageous embodiment a lamp
`according to the invention comprises a discharge enve-
`lope, a ballast unit and an ignition unit, and Optional
`reflectors, all in a common envelope consisting of a
`bottom portion comprising a cap and an outer bulb
`transparent to radiation, and is characterized in that an 65
`absorption layer is disposed on at least parts of the sur-
`face of the ballast unit and/or ignition unit and/or of the
`bottom portion and/or the reflectors.
`
`4,727,283
`
`4
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`Embodiments of lamps according to the invention
`will now be described more fully with reference to the
`drawing in which:
`FIG. 1 shows in elevation and partly broken away a
`low-pressure mercury vapour discharge lamp compris-
`ing two parallel tube portions interconnected by a cou-
`pling tube, and
`FIG. 2 shows diagrammatically a low-pressure mer-
`cury vapour discharge lamp capped on one end, which
`is suitable to replace incandescent lamps.
`DESCRIPTION OF THE PREFERRED
`EMBODIMENTS
`
`The lamp shown in FIG. 1 comprises a glass dis-
`charge envelope 1 sealed in a gas-tight manner and
`comprising two parallel tube portions 2 and 3 intercon-
`nected by a coupling tube 4. The discharge envelope 1
`contains a small quantity of mercury and argon at a
`pressure of 400 Pa and is further provided at its inner
`surface with a luminescent layer 5. The layer 5 com~
`prises a red luminescing yttrium oxide activated by
`trivalent europium and a green luminescing terbium-
`activated cerium magnesium aluminate. An electrode
`(not shown in the drawing) is arranged at each of the
`ends of the tube portions 2 and 3 remote from the cou—
`pling tube 4 and these electrodes constitute the means
`for maintaining a column discharge in the gas filling.
`The ends of the tube portions 2 and 3 located near the
`electrodes are connected to a lamp base 6, which carries
`two current-supply pins 7 and 8 and in which a glow
`starter (not shown) is arranged. The discharge envelope
`1 is coated throughout its outer surface with a thin
`absorption layer 9 of yttrium aluminate activated by
`trivalent cerium having a garnet structure. The inner
`diameter of the tube portions 2 and 3 is 10 mm and the
`length of the U-shaped discharge path is about 200 mm.
`During operation, the lamp comsumes a power of 9 W
`and the load of the luminescent layer 5, Le. the power
`consumed by the column divided by the surface area of
`the luminescent layer 5, is about 1350 W/mz.
`The lamp of FIG. 2 has an envelope 1 comprising a
`glass outer bulb 2 and a bottom portion 3, which is
`connected to the bulb and is provided with a cap in the
`form of an E 27 lamp base 4. In the envelope 1 are
`arranged a discharge bulb 5, a ballast unit 6 and an
`ignition unit (not shown in the drawing) provided in the
`bottom portion 3. The discharge bulb 5 comprises a
`glass tube having an inner diameter of 9.5 mm, this tube
`being bent into the shape of a hook comprising four
`adjacent parallel extending tube portions intercom
`nected by three curved tube portions. The discharge
`bulb 5 contains a small quantity of mercury and an
`amalgam and a mixture of argon and neon at a pressure
`of 300 Pa. Electrodes 7 and 8, respectively, are arranged
`at the ends of the bulb 5 and the inner surface of the bulb
`5 is provided with a luminescent layer 9 comprising red
`and green luminescing materials of the type mentioned
`in FIG. 1. The bulb 5 is arranged with its free ends in a
`bottom plate 10, which is secured in the bottom portion
`3. The bottom plate 10 and the ballast unit 6 are coated
`with thin absorption layers 11 and 12, respectively, of
`cerium-activated yttrium aluminate. The lamp con-
`sumes during operation a power of 18 W. The length of
`the curved discharge path is about 390 mm and the
`power consumed by the column divided by the surface
`
`TCL 1029, Page 4
`TCL 1029, Page 4
`
`

`

`5
`2
`area of the luminescent layer 9 has a value of 1250
`Wm '
`
`4,727,283
`
`6
`
`TABLE II
`ex. A (mg)
`x
`y
`R (a.8>
`Loam)
`Llooo (1m)
`
`a
`o
`0.457
`0.411
`82
`564
`502
`g
`:3
`3:13:
`3:32
`:1
`:22
`:3:
`
`0,444.0.430757 513 30 565
`
`
`
`
`
`
`5
`
`EXAMPLES 1 T0 4
`Four lamps (designated 1 through 4) of the type de-
`scribed with reference to FIG. 1 (9 W) were provided
`with a thin uniform absorption layer of cerium-
`activated garnet according to the formula Y2.9Ceo.1Al-
`.
`.
`.
`.
`5012’ which layer was disposed on the outer surface of
`It is again seen that the absorption layer leads to a shift
`-
`.
`of the colour point by about Ay=1.5Ax. The lamps 5, 6,
`ficgflfisuflbifli fglingigel-iblilifif:2:23:11]- 10 and 7 all had a luminescent layer with the same ratio of
`mass of the garnet used in the absorption ’layer (A in
`the quantity of red luminescing material to that of the
`mg), the colour point (Ly) of the light emitted by the
`green luminescing material as the lamp a, which has a
`lamp and the luminous flux obtained (L in lumen) are
`colour temperature .of about 2750 K. A small enlarge-
`indicated for each of these lamps. For comparison, (x, 15 ment or this ratio yields for the lamp 5 a €019“ pomt
`y) and L were measured on a lamp designated a) with-
`near the line of the black body radiators, in which event
`out an absorption layer, but otherwise identical to the
`the C9101" temperature 18 about 2500 K' In a corre-
`lamps 14_ These value also indicated.
`spending manner, even lower colour
`temperatures
`(down to about 2000 K.) can be attained for the lamps 6
`TABLE I
`20 and 7_
`4
`L (lm)
`y
`x
`EXAMPLE 8
`A (mg)
`example
`564
`0.411
`.
`0.457
`.
`o
`a
`558
`0.429
`0.468
`A lamp (8) of the kind described With reference to
`59
`i
`542
`0'434
`0~47°
`FIG. 2 (18 W) was provided with a Y2,9Ceo.1 A1501:-
`72
`2
`
`
`
`
`
`2 25 containing absorption layer disposed on the bottom 1:3 8:3; 3:33 :3:
`plate on the ballast unit and on the side of the upright
`edge of the bottom portion facing the discharge bulb.
`The lamp had a colour point of the emitted radiation
`It clearly appears that With increasing thickness 0f the
`x=0.465 and y=0.417, which is very close to the de-
`absorption layer an increasing Shift 0f the C010“! point
`occurs, where total AY=1-5AX- The 0010‘“ temperature 30 sired point (x=0.468 and y=0.418). An identical lamp,
`0f the light emitted by the lamp 3 is about 2750 K and
`but without an absorption layer, had a colour point
`the colour point lies substantially on the line of the black
`x=0.461 and y=0.412.
`.body radiators.
`EXAMPLES 9 T0 11
`If now in the luminescent layer of the lamps 1—4 the
`Three lamps (9, 10 and ii) of the kind described with
`ratio of the quantity of red luminescing material to the 35
`reference to FIG. 2 (18 W) were provided with a lumi-
`'quantity 0f the green luminescing material is enlarged
`nescent layer consisting of a mixture of green luminesc-
`(this ratio must be larger as the absorption layer is
`ing terbium-activated cerium magnesium aluminate
`. thicker) 30 that the COiO‘h' 130th Of the lamp shifts to 3“
`(CAT), red luminescing yttrium oxide activated by
`area on or rim the line of the black body radiators, a
`colour temperature is attained of about 2400, 2340, 2200 40 trivalent europium (YOX) and cerium-activated garnet
`and 2000 K for the lamps 14. reSPectiveIY-
`.
`(YAG) according to the formula Y2‘9Ceo,1A15012. In
`EXAMPLES 5 TO 7
`these lamps, the luminescent layer therefore also ful-
`_
`.
`filled the function of absorption layer. In the following
`Three lamps (5, 5 and 7) 0f the kind shown in FIG- 1
`Table III, the composition of the luminescent layer (in
`(9 W), hilt without an outer absorption layer, were 45 % by weight) of the colour point (x, y), the colour
`coated on the inner Side of the discharge bulb With
`temperature (Tc in K.), luminous efficacy ('0 in 1 m/W)
`varying thicknesses Of an absorption layer 0f cerium-
`and the general colour rendition index R (a, 8) are indi-
`activated garnet according to the formula Y2,9Ceo.1Al-
`cated for these lamps.
`-
`TABLE III
`——.________..___.—___________
`
`1)
`Tc
`YAG
`YOX
`CAT
`——-———_—_____—____.__.—_____
`example % by weight % by weight % by weight
`(K)
`(lm/W)
`x
`y
`R (3.8)
`9
`30.8
`66.5
`2.7
`0.477 0.414 2500
`49.0
`80
`10
`26.8
`67.9
`5.3
`0.493 0.415
`2325
`48.4
`82
`ll
`23.0
`68.1
`8.9
`0.508 0.4!5 2175
`47.6
`83
`——-———_———_—__
`
`Finally, it should be noted that the luminescent layer
`of a lamp according to the invention may comprise
`5012. Onthis absorption layer, aluminescent layer con-
`sisting of a mixture of red luminescing Y203-Eu3+ and 60 besides a red luminescing and a green luminescing mate-
`green luminescing CeMgAanig-Tb is provided. In the
`rial also a small quantity of a blue luminescing material,
`following Table II, for each lamp the mass of the ab-
`as is also the case in three-band fluorescent lamps hav-
`sorption layer (A in mg), the colour point (x, y), the
`ing a high colour temperature. In the present heavily
`general colour rendering index R (a, 8), the luminous
`loaded lamps, this can afford advantages because the
`flux at 0 hours (L0 in l m) and the luminous flux after 65 blue luminescing material provides an additional degree
`1000 operating hours (Liooo in 1 m) are indicated. For
`of freedom for reaching a desired value of the colour
`comparison, these values are also indicated for the lamp
`point of the lamp.
`a without an absorption layer.
`What is claimed is:
`
`TCL 1029, Page 5
`TCL 1029, Page 5
`
`

`

`7
`1. A low-pressure mercury vapour discharge lamp,
`whose emission mainly lies in three spectral ranges and
`whose colour temperature of emission lies in the range
`of 2000—3000 K., the lamp comprising a gas-tight dis-
`charge envelope transparent to radiation and having a 5
`gas filling comprising mercury and a rare gas, a lumines-
`cent
`layer comprising luminescent materials whose
`emission mainly lies in the ranges of 590—630 nm and
`520-565 nm, means for maintaining a column discharge
`in the gas filling, the power consumed by the column 10
`being at least 500 W per in2 surface area of the lumines-
`cent layer,
`characterized in that the lamp is provided with an
`absorption layer comprising a luminescent alumi-
`nate activated by trivalent cerium and having a 15
`garnet crystal structure.
`2. A lamp as claimed in claim 1, characterized in that
`the luminescent aluminate having a garnet structure
`corresponds to the formula Ln3.xCexAls.p.anpch012,
`in which Ln is at least one of the elements yttrium, 20
`gadolinium, lanthanum and lutetium and in which
`0.01 .5. x; 0. 15
`0§p§3
`.
`Oéqél.
`3. A lamp as claimed in claim 2, characterized in that 25
`Ln is yttrium and p=q=0.
`4. A lamp as claimed in claim 3, characterized in that
`the absorption layer is disposed on the outer surface of
`the discharge envelope.
`5. A lamp as claimed in claim 3, characterized in that 30
`the absorption layer is disposed on the inner surface of
`the discharge envelope and in that the luminescent layer
`is disposed on the side of the absorption layer facing the
`discharge.
`6. A lamp as claimed in claim 3, characterized in that 35
`the garnet activated by trivalent cerium is mixed with
`the luminescent materials of the luminescent
`layer
`whereby the luminescent layer also is the absorption
`layer.
`7. A lamp as claimed in claim 3, including a ballast
`unit and an ignition unit, which are arranged together
`with the discharge envelope in a common envelope
`consisting of a bottom portion comprising a cap and of
`an outer bulb transparent to radiation, characterized in
`that the absorption layer is disposed on at least parts of 45
`the surface of one or more of the ballast unit, the igni-
`tion unit and the bottom portion.
`8. A lamp as claimed in claim 2, characterized in that
`the absorption layer is disposed on the outer surface of
`the discharge envelope.
`
`50
`
`4,727,283
`
`8
`9. A lamp as claimed in claim 1, characterized in that
`the absorption layer is disposed on the outer surface of
`the discharge envelope.
`10. A lamp as claimed in claim 2, characterized in that
`the absorption layer is disposed on the inner surface of
`the discharge envelope and in that the luminescent layer
`is disposed on the side of the absorption layer facing the
`discharge.
`11. A lamp as claimed in claim 1, characterized in that
`the absorption layer is disposed on the inner surface of
`the discharge envelope and in that the luminescent layer
`is disposed on the side of the absorption layer facing the
`discharge.
`12. A lamp as claimed in claim 2, characterized in that
`the garnet activated by trivalent cerium is mixed with
`the luminescent materials of the luminescent layer and
`in that the luminescent layer also is the absorption layer.
`13. A lamp as claimed in claim 1, characterized in that
`the garnet activated by trivalent cerium is mixed with
`the luminescent materials of the luminescent layer and
`in that the luminescent layer also is the absorption layer.
`14. A lamp as claimed in claim 2, including a ballast
`unit and an ignition unit, which are arranged together
`with the discharge envelope in a common envelope
`consisting of a bottom portion comprising a cap and of
`an outer bulb transparent to radiation, characterized in
`that the absorption layer is disposed on at least parts of
`the surface of one or more of the ballast unit, the igni-
`tion unit and the bottom portion.
`15. A lamp as claimed in claim 1, including a ballast
`unit and an ignition unit, which are arranged together
`with the discharge envelope in a common envelope
`consisting of a bottom portion comprising a cap and of
`an outer bulb transparent to radiation, characterized in
`that the absorption layer is disposed on at least parts of
`the surface of one or more of the ballast unit, the igni-
`tion unit and the bottom portion.
`16. A lamp as claimed in claim 7, including at least
`one reflector arranged within the envelope, character-
`ized in that the adsorption layer is disposed on at least a
`portion of the surface of the reflector.
`..
`17. A lamp as claimed in claim 14, including at least
`one reflector arranged within the envelope, character-
`ized in that the absorption layer is disposed on at least a
`portion of the surface of the reflector.
`18. A lamp as claimed in claim 15, including at least
`one reflector arranged within the envelope, character-
`ized in that the absorption layer is disposed on at least a
`portion of the surface of the reflector.
`#
`t
`i
`t
`*
`
`55
`
`65
`
`TCL 1029, Page 6
`TCL 1029, Page 6
`
`