Nov. 19, 1940.
H. KUDAR
2,222,414
PROJECTION SYSTEM
Filed Feb. 15, 1937
. Inventar
170/76 KIA/an
Attorneys
‘ Patented Nov. 19, 1940
'
UNITED STATES
2,222,414
‘
' PATENT OFFICE
2,222,414
PROJECTION SYSTEM
Hans Kudar, Berlin-Schoneberg, Germany, as- ‘
signor to Telelunken Gesellschai't iiir Drahtlose
Telegraphic m. b. IL, Berlin, Germany, a corpo
ration of Germany
Application February 15, 1937, Serial No. 125,856
In Germany February 13, 1936
6 Claims. (01. 88-24)
My .invention relates to a method of and means Anteriorly of the television receiver screen on
the projection screen there should then be
for clearly showing luminous pictures, more par
ticularly television images upon ?uorescent mounted another ?lter in addition to the neo
screens and cinematographic pictures upon a dymium ?lter in or in front of the screen, the
said second ?lter being adapted to absorb the 5
5 projection screen, in illuminated rooms.
second mentioned light.
It is well known that for clearly showing pro
The ?lter may be mounted at any convenient
jected or ?uorescent pictures the room has to be
point between the television picture and the eye.
darkened so as to avoid an undesirable illumina
For instance, the bulb of the cathode-ray-tube
tion of the picture screen.
I
of a television receiver of the cathode-ray type,
According to the invention projected or ?u
10
orescent pictures of any kind can be clearly
shown in illuminated rooms without any sub
stantial undesirable illumination of the picture
Screen by using arti?cial light having a narrow
spectral range for lighting the room, and using
a picture screen made out of a material adapted
to absorb the spectrum of the room illumination,
or protecting the picture screen from the effect
of the room illumination by a ?lter pane consist
ing of such a material and arranged in front of
thepicture screen. The light sources for lighting
the room may emit one or more substantially
monochromatic radiations and the absorbing
0
medium contained in the picture screen or in the
‘*5 ?lter arranged in front of it should be opaque
substantially only within the spectral range or
ranges of the light sources. It has been found
that it is particularly advantageous to use sodium
vapor lamps for the room illumination, and neo
30 dymium as absorbing medium for protecting the
picture screen against illumination by the light
of said light sources. The sodium vapor lamp
emanates practically monochromatic yellow light
of a wave length between 570 and 600W. and a
translucent material like glass containing neo
dymium absorbs this very wave-length while it
permits all other wave-lengths of the visible spec
trum to penetrate through it almost undimin
ished.
If a fluorescent screen is used ‘of a kind
producing comparatively white light‘, or substan
tially white light is used for projecting a picture,
‘then, in an arrangement of this invention, the
said white light is transmitted with the excep
tion of the yellow D-line, and the result is a per
-' fectly natural reproduction of the ?uorescent or
projected picture.
If the requirements regarding the room illumi
nation are severer, then another single-wave may
be added to the one before mentioned, with the
result that the ?rst radiation is so supplemented
that the ensuing light will be as agreeable and
pleasing as possible to the eye, For instance,
what may be added to the yellow sodium vapor
r light is a red or a bluish light, and also the lat
ter should be practically single-wave in nature.
or at least the screen wall of the tube, may be
made of the ?lter glass. Another embodiment
consists in that the protective pane mounted an
teriorly of the cathode-ray tube and which is to
protect the eyes of the ?lter in case of accidental
breaking of the tube, ‘is made of filter glass; for
instance, the safety glass marketed under the.
trade-name of “Sekurit” and consisting of sev
eral glass sheets could have incorporated in it a
certain addition of neodymium, or, for a room an
illumination consisting of two monochromatic
radiations, each one of the glass sheets of such
glass may contain an absorbing medium adapted
to absorb one of the radiations forming part of
the room illumination.
A projection screen to be used for projecting
pictures according to the invention may consist of
a frosted mirror plate made of glass containing
neodymium or .didymium.
In the drawing two embodiments of the inven- 30
tion are shown diagrammatically by way of ex
ample:
Fig. 1 shows an arrangement for showing tele
vision pictures,
'
Fig. 2 illustrates the use of the invention for 35
showing cinematographic pictures.
'
The source of illumination l is a sodium-vapor
lamp. In its stead could also be used a luminous
source giving off light comprising several wave
lengths, while in front thereof would then be ‘0
?tted a ?lter designed to transmit‘ only single
wave light. The television tube 2 is mounted
posteriorly of a protective pane 3 which is ?tted
into the casing 4 of the television receiver. The
said pane 3 serves two different purposes at the 45
_ same time:' (1) it safeguards the viewer from
scattered glass chips in case of accidental burst
ing of ,the television tube, and (2) the pane is
of such a composition that it will permit nearly
all wave-lengths inside the visible spectrum to 50
penetrate and pass with the exception of the
light of luminous source I. The said pane 3
consists preferably of neodymlferous glass. An
other plan would be to mount a so-called “Se
kurit” glass (safety) pane adjacent or in juxta- 55
2
2,222,414
position with a neodymiferous glass pane. Even
if a ?uorescent screen is employed which trans
mits a very wide spectrum including also the d
line, the pane I, because of the low percentage of
(1 line light in the entire spectral range of the
?uorescent light will occasion a hardly appreci
able attenuation of the luminosity of the tele
yision image.
There is no absolute need for the pane I being
10. built into the casing l, in fact, it could be mount
ed at some suitable place between the ?uorescent
screen and the viewer. Even if the light issued
from source I should be able to directly strike
the fluorescent screen 2 of the tube 2, the ar
.18 rangement will be e?icient provided that the
pane I is mounted somewhere in front of the
viewer's eye.
The present invention is not con?ned to the
viewing of television images. For instance, in
lieu of the ?uorescent screen of tube 2 there
could be used also a ground glass (matted) pane
upon which a picture is projected. Because of
the fact that pane l is mounted, this image
would be visible from the illuminated room con
taining the onlookers just as is true of a cath
predetermined narrow bands of frequencies, pro
jecting a picture in light of different frequencies
from that of the light illuminating the room on
a viewing surface normally illuminated by said
light of narrow bands of frequencies within the
room, and absorbing substantially only the light
of said predetermined frequencies which is di
rectly in register with the viewing surface to
provide pictures of maximum contrast and undi
minished intensity for an observer.
.
10
3. A device for showing luminous pictures in
illuminated rooms, comprising a picture screen
for producing luminous pictures within a room,
means for lighting the room and said screen by
light having a narrowspectral range and different 15
from the spectral range of the luminous pictures,
and an absorbing medium positioned adjacent
to the picture screen and intermediate the light
ing means and the picture screen and also posi
tioned between said screen and an observer, said
absorbing medium absorbing light substantially
only in the same region as the narrow spectral
range of the lighting means, whereby pictures of
maximum contrast are viewed by the observer..
4. A device for showing television images upon
ode-ray tube. It would also be possible to dis
a ?uorescent screen in an illuminated room,
pose a wall at relatively great distance poste
riorly of the pane 3, upon which wall a picture
could be projected from the side of pane 3. In
comprising a television receiver wherein is pro
vided a cathode ray tube having a ?uorescent
screen upon which images of predetermined spec
tral emission are produced, means for lighting 30
the room and said tube by light having a narrow
spectral emission range di?erent from the spec
tral emission of the fluorescent screen, and
face, the projector could be arranged anteriorly
of the pane 3 provided the cone of light is made
to laterally skirt the said pane. In this man
ner motion-picture projection would be feasible
even in brightly lit rooms or auditoriums.
The television receiver shown in the drawing
may be of the type described in U. S. Patent No.
1,975,056 to W. L. Carlson, issued September 25,
1934.
In Fig. 2 the light source I is again a sodium
I vapor lamp while the light source 5 is a high
pressure mercury vapor lamp emanating in first
line blue light of a wave length of 436 an. The
projector 8 has a light source emitting substan
tially white light. The projection screen 1 con
. sists of a frosted mirror plate made of glass con
taining neodymium, and in front of this screen
there is an ordinary yellow ?lter 8 for protecting
the screen from being illuminated by the blue
light of the mercury vapor lamp 5. The screen
1 1 and the filter 8 are mounted in the frame 9.
What I claim is:
1. The method of showing luminous pictures
in an illuminated room, which comprises illu
minating the room with light of a predeter
‘mined narrow band of frequencies, projecting
a picture in light of diiferent frequencies from
that of the light illuminating the room on a
viewing surface normally illuminated by said
light of narrow band of frequencies within the
‘room, and absorbing substantially only the light
of said predetermined frequencies which is di
rectly in register with the viewing surface to
provide pictures of maximum contrast and undi
minished intensity for an observer.
. 2. The method of showing luminous pictures
in an illuminated room, which comprises illu
minating the room with light of a plurality of
means for absorbing only light substantially
within the spectral range of the lighting means,
said absorbing means being positioned adjacent
8.5.
to the ?uorescent screen and intermediate the
?uorescent screen and lighting means and lo
cated between said screen and an observer,
whereby produced images of maximum contrast 40
are viewed by said observer.
5. A device for showing projected cinamato
graphic pictures in illuminated rooms compris—
ing a projection screen, means for projecting
pictures in light of wide spectral range upon the 45
projection screen, means for lighting the room
and said screen by light having a narrow spec
tral range, and an absorbing medium positioned
adjacent to the projection screen and interme
diate the projection screen and light means and 50
also positioned between said screen and an ob
server, said absorbing medium absorbing light
substantially only the same as the spectral range
of the lighting means whereby the projected pic
tures of maximum contrast and undiminished 55
intensity are viewed by said observer.
6. In combination, a picture viewing area with
in a room, a sodium vapor lamp illuminating
said room and said viewing area, and a sheet
of neodymium glass positioned adjacent to the 60
viewing area and intermediate the viewing area
and the sodium lamp, said sheet being between
said viewing area and an observer, whereby pic
tures of maximum contrast are viewed by said
observer.
>
HANS KUDAR.
66