Note: Descriptions are shown in the official language in which they were submitted.
PHN. 8371.
~01~1306
The invention relates to a lcw-pressure
mercury vapour discharge lamp having a colour rendering
index Ra of at least 80, the lamp having a filling comr
prising mercury and a r æe gas, and a luminescent layer
emitting in the three wavelength ranges of 430 to 490
nm, from 520 to 565 nm, and frcm 590 to 630 nm, the
emission in the range fron 590 to 630 nm being nainly
produoed by a luminescent rare earth metal oxide
activated by trivalent europium.
Such fluorescent lamps which emit in
three relatively narrow wavelength ranges æe kncwn,
for example, from United Ringdom patent specification
1,458,700 which issued to Philips Electronic and
Associated Industries Limited on December 15, 1976.
By means of these lamps a high luminous efficiency,
for example 70 lm/W or higher can be obtained in ccmr
bination with a good colour rendition. A good
colour rendition must here be underst~od to mean that
the general CIE colour rendering index Ra has a value
of 80 or higher. In general these lamps have a ~;
luminescent layer with three lumines oe nt materials
which each radiate in one
B~
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PHN 8371
10.2.1977
1081306
of the three above-mentioned spectral ranges.
By a suitable choice of the ratio of the qu~-
tities of these three luminescent materials, it
is possible to obtain colour temperatures of the
radiation emitted by the lamp in a relatively
wide range, for example ~tween 2300 and 6800 K.
In the above-mentioned United
Eingdom patent specification 1,458,700, rare
earth metal oxides activated by trivalent euro-
pium, particularly Eu3~-activated yttrium oxide,
are mentioned as being the most suitable red
luminescing materials for use in law- pressure
mercury vapour discharge lamps having an Ra f
at least 80 and a luminescent layer emitting
in the three wavelength ranges of 430 to 490 nm,
from 520 to 656 nm and from 590 to 630 nm. These
oxides have, namely, a high quantum efficiency
so that high luminous fluxes can be obtained.
It has appeared, however, that the prior art
lamps provided with these oxides have a not
very satisfactory rendition of deep red and
deep purple colours. This is a result of the
fact that said oxides emit in a few narrow
lines, the strongest of which is located at
611 nm. ~t appears, however, that ln the red
part of the spectrum deep-red and deep-purple
objects reflect radiation to a considerable
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PHN 8371
10.2.1977
1081306
degree only at wavelengths which exceed
6~5 nm. It is therefor a disadvantage of
the prior art lamps that the colour rendition
of the human skin may be not so good sometimes.
This is especially then the case if the blood
vessels are in the upper layers of the skin.
Then too great a contrast is created between
the colour of these blood vessels, which have
a considerable reflection in the deep-red part
of the spectrum, and the colour of the skin
itself.
It is an object of the invention
to pro~de fluorescent lamps emitting in the
three above-mentioned spectral ranges, and
which have an improved rendition of deep-red
and deep-purple colours.
The inventi~n provides a low-
pressure mercury vapour discharge lamp having
a colour rendering index of at least 80, the
lamp having a filling comprising mercury and a
rare gas, and a luminescent layer which emits
in the three wavelength ranges from 430 to
490 nm, from 5Z0 to 565 nm, and from 590 to
630 nm, the emission in the range from 590 to
630 nm being mainly produced by a luminescent
rare earth metal oxide activated by trivalent
europium, and wherein the luminescent layer
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PHN 8371
10-2.1977
~081306
comprises from 2 to 10~ by weight of a luminescent
B Oxysulphide of yttrium and/or lanthanum activated
by trivalent europium.
A lamp according to the invention
comprises, besides the Eu3+-activated oxide a
comparatively small quantity of Eu3~-activated
oxysulphide. These oxysulphides of yttrium nnd/or
lanthanum which are known per se emit, in some
narrow spectral lines. For the oxysulphide~
however, the highest emission is found at 627 nm.
A result of this additional emission in the red
part of the spectrum is that wil;h the lamps
according to the invention, a considerable im-
provement of the rendition of deep-red and
purple colours, especially of the colour of the
skin, can be obtained.
It could be expe~ted that the
use of oxysulphide as red-emitting component
in the luminescent layer would entail a reduc-
tion in the luminous flux of the lamp, as onthe one hand the quantum efficiency of these
materials is lower than that of the correspon-
ding oxides, and, on the other hand, the sensi-
tivity of the eye for the deep-red radiation
emitted by these oxysulphides is lower than that
for the radiation deriving from the corresponding
PHN. 8371. -
108~306
oxides. It has surprisingly been fo~nd that the
lamps according to the invention have a lu~inous
flux which is not, or is not substantially,
lcwer than that of the prior art lamps. However,
the luminescent layer should not contain m~re
than 10 % by weight of the oxysulphide. When
less than 2 ~ by weight of oxysulphide is used
the improvement in the colour rendition is too
small.
In a lamp according to the inven-
tion a luminescent layer is preferably used
which contains a Eu2 or Eu2 and Mh2 _ activated
aluminate of Ba and/or Sr and, optionally, of Mg.
me above-mentioned binary or ternary aluminates
have a hexagonal crystal structure which is
related to that of the hexagonal ferrites and are
further described in United Kingdom patent speci-
fication 1,190,520, 1,384,683 and 1,452,083
which issued to Philips Electronic and Associated
Industries Limited on May 6, 1970; February 19,
1975 and Octdber 6, 1976 respectively. mese
aluminates are particularly efficient blue-
luminescing materials whose emission spectra are
very suitable ~or use in these la~s. As green-
luminescing components, a
B - 6 -
PHN 8371
10.2.1977
10~31306
- . terbium-activated aluminate of
cerium and, optionally, of magnesium is
preferably used. These aluminates have a
crystal structure which is analogous to that
of the blue-luminescing aluminates and are
described in United Kingdom patent specifi-
cation 1,452,083. Eu3+-activated yttrium
~ ~X~ d~
ulphidc is preferably used as luminescent
material which yields most of the radiation in
the red part of the spectrum and Eu3~-activated ,
yttrium oxysulphide is preferably used as
deep-red emitting component according to the
invention.
Some embodiments of the inven-
tion will now be described with reference to
two Tables, the Examples and to the acoompany-
ing drawing, the single Figure of which shows
diagrammatically a longitudina] section of a
low-pressure mercury vapour discharge lamp
according to the invention.
The lamp has a glass envelope 1
with electrodes 2 and 3located at opposite ends.
The lamp has a filling consisting of a mixture
of a rare gas which serves as starting gas and
a small quantity of mercury. The inside of the
envelope 1 is coated with a luminescent layer 4
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PHN 8371
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1081306
which contains a mixture of luminescent ma-
terials according to the invention. The
luminescent materials can be applied in a
custormary manner to the envelope 1, for
example by means of a suspension containing
the luminescent materials.
A number of 40 watt lamps of
the type shown in the drawing were provided
with a luminescent coat containing luminescent
materials having emissions in the spectral
ranges indicated above. For each lamp the
composition of the mixture of luminescent
materials was chosen such that the colour
temperature of the radiation emitted by the
lamp was 4000 K. All lamps contained europium-
activated yttrium oxide (referred to in the
Tables as Y2o3-Eu3+) as a red-luminescing
material, terbium-activated cerium magnesium
aluminate (referred to in the Tables below
as aluminate-Tb3+) as green-luminescing
material and europium-activated barium magne-
sium aluminate (referred to in the Tables as
aluminate-Eu ~) as blue-luminescing material.
Table 1 defines the composition (in weight %)
of the luminescent layer of these lamps and a
summar~y of the results of measurements made on
PHN 8371
10.2.1977
1081306
lamps. These lamps specified under A (not
according to the invention) have a prior
art mixture of luminescent material and have
only been included in Table 1 for comparative
purposes. The lamps according to the inven-
tion (I, II and III) contain as an additional
red-luminescing component the specified quan-
tity of europium-activated yttrium oxysulphide
(Y2o2S-Eu3+). Listed under the headin6 measure-
ments are the luminous flux of the lamp after300 operating hours in Lm/W (L0300), the value
of Ra (general colour rendering index), the
value of R9 (colour rendering index for deep-
red colours), and the so-called red percen-
tage (red %), that is to say the luminous fluxemitted by the lamp having wavelengths exceeding
approximately 615 nm in a percentage of the
total luminous flux. Finally, under the heading
"figure of merit", Table 1 gives for the lamps
A, II and III aLfigure which is a measure for
the natural colour rendition quality which is
obtained by means of visual comparison and
judgement by a number of persons (52) of the
colour rendition of a great number of objects.
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1081306 PHN 8371
10.2-1977
TABLE 1 (Colour temperature 4000 K)
Composition (% by weight)!
Y2o3-Eu3+ ~ 5- 49.0 1 47.0 1 45.0
! Y2o2s-Eu3+ I o.o 3-0 5.6 ' 8.1
' Aluminate-Tb3+ ¦ 35.o 34.0 33.0 ~ 32.4
Aluminate-Eu2+ ¦ 15.0l 14.0 14.4 1 14.5
Measurements ~
I , .
, L0300 1 78.6 78.4 , 78.2 77-2
.~ Ra ¦ 85 85 i 86 ~ 86
10 '' Rg ~ 44 46 ¦ 5 ~ 55
red % 2.6 2.8 ~ 2.9 ! 3.
¦ figure of merit 100 ~ - ~ 188
Results of lamps, analogous to
the lamps described above but having a colour
temperature of the emitted radiation of 3000 K
are shown in the table II which follows here-
below.
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PHN 8371
lOB1306 10.2.1977
TABLE II (colour temperature 3000K)
~~ ~ - IV I V
Composition (% by weight) ~_. _ ~ . ~ . .L ___ _
1 Y20J-EU3+ 64.o 62.0 160.0
5 ~ Y2o3s-Eu3+ 0.0 3. 15.5
Aluminate-Tb3~29.0¦ 28.0 127-5
~l Aluminate-Eu2+.7.0 1 7.0 17.0
! Measurements ~
, L0100 ! 80 ~ 81 ,80 .j
10 ~ Ra 182 1 82 182
'1~ Rg 29 1 33 1. 4
The lamps listed under in
Table 2 under B do not contain Y2o2S-Eu3+
(hence these lamps are not according to the
invention) and have been included for compa-
rative purposes. The luminous flux measurements
: (in Lm/W) for these lamps were performed after
100 operating hours (L0100).
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