U.S. patent number 3,704,928 [Application Number 05/087,792] was granted by the patent office on 1972-12-05 for dental light with dichroic and infrared filters.
This patent grant is currently assigned to Sylvania Electric Products, Inc.. Invention is credited to Peter M. Coombs, Ernest Davey, Conrad Edward Kowalski.
United States Patent |
3,704,928 |
Coombs , et al. |
December 5, 1972 |
DENTAL LIGHT WITH DICHROIC AND INFRARED FILTERS
Abstract
A fixture for dental illumination, in which an elliptical
reflector and light source is used with a light gate and projection
lens, these being set in an enclosing canister with the light
emerging through the lens, an infrared filter in the path of the
light rays to absorb unwanted heat radiation, and a dichroic filter
on the surface of the lens facing the reflector to correct the
light-rendering index of the emitted light. Without any filter,
neither infrared nor visible, the color rendering index of the
light from the device is 97.5. When the infrared filter is added,
this drops to 88.0, but the addition of the dichroic visible-light
filter brings this back to 97.5, which is very good.
Inventors: |
Coombs; Peter M. (Newton,
NH), Davey; Ernest (Lynn, MA), Kowalski; Conrad
Edward (Marblehead, MA) |
Assignee: |
Sylvania Electric Products,
Inc. (N/A)
|
Family
ID: |
22207296 |
Appl.
No.: |
05/087,792 |
Filed: |
November 9, 1970 |
Current U.S.
Class: |
359/359; 359/890;
359/581; 362/804 |
Current CPC
Class: |
F21V
9/04 (20130101); F21V 9/08 (20130101); G02B
6/0005 (20130101); F21V 7/22 (20130101); F21V
7/08 (20130101); Y10S 362/804 (20130101); F21W
2131/202 (20130101) |
Current International
Class: |
F21V
8/00 (20060101); F21V 9/00 (20060101); F21V
9/08 (20060101); F21V 7/08 (20060101); F21V
7/00 (20060101); F21V 9/04 (20060101); F21S
8/00 (20060101); G02b 005/22 () |
Field of
Search: |
;350/1,163-166,316
;240/41.15,41.3 ;353/55 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Degenkolb, et al., "Dichroic Safeguards," Journal of the S.M.P.T.E,
Vol. 76, No. 1, Jan. 1967, pp. 15-17.
|
Primary Examiner: Schonberg; David
Assistant Examiner: Kusmer; Toby H.
Claims
What we claim is:
1. A dental lighting fixture comprising:
an optical system including an ellipsoidal reflector having a light
source disposed at one focus thereof;
a fixed light gate disposed in front of said optical system, said
gate having a rectangular opening disposed at the other focus of
said ellipsoidal reflector;
a lens disposed in front of said light gate, said lens having a
spheric side facing said light gate, the other side of said lens
being aspheric;
a dichroic coating disposed on said spheric side of said lens, said
coating having higher transmission of blue light than of green,
yellow, orange or red light; and
an infrared absorbing glass filter disposed in front of said lens,
the combination of said dichroic coating and said filter yielding
light of high color rendering index.
Description
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates to fixtures for dental illumination, and in
particular to such fixtures which utilize a heat-absorbing filter
to prevent excessive heating of the patient's face by infrared
radiation.
2. Brief Summary of Prior Art
Dental fixtures have been developed using a light source at one
focus of an ellipsoidal reflector, and at the other focus a gate
having an opening defining the extent of the beam. These provide a
high intensity of light on the patient's face, but since the light
source is an incandescent lamp, most of its radiated energy is
infrared, which does not assist the dentist in seeing, but can
undesirably heat up the face of the patient on which it falls. A
filter plate is used in front of the lens, that is between the lens
and the patient's face to absorb the infrared and produce a cooler
light.
The usual infrared filters have a broad cutoff and also absorb
visible light in some parts of the spectrum. The quality of the
light emitted from the fixture without the filter is such that its
color-rendering index is 97.5, which is considered excellent, but
the addition of the filter drops this index to 88, which is
undesirable, since the dentist needs to see the patient's teeth in
their natural colors.
The glass filters available for cutting off the far infrared are
found to transmit more in the green and yellow than in the blue,
and since the incandescent source is comparatively low in blue
radiation, this means that the green light will predominate and
give the light a greenish tinge which is undesirable.
BRIEF SUMMARY OF INVENTION
It is here that our invention solves the problem by using an
additional filter which cuts down on the green and has high
transmission for the blue. The filter also cuts down on the yellow,
orange and red somewhat, but since the source is rich in these
colors anyway, this merely helps to give a balanced light. The
color temperature is raised to an acceptable balance, and the color
rendering index is brought back to 97.5. We have discovered that
this filter can best be utilized by making it of the dichroic type,
which can be coated onto some light-transmitting part of the
device. The dichroic filter was tried at the light gate, but the
high radiation density at that point destroyed the dichroic
coating. A coating on the back of the infrared filter, that is, on
the side nearest the lens, was found to give secondary reflections
back onto the gate, which was transmitted into the illuminating
pattern, which was undesirable. A third approach was tried by
coating the external surface of the infrared filter, but this left
the coating vunerable to abrasion when cleaned.
We have discovered that all these disadvantages can be overcome by
having a dichroic coating on the lens surface which faces the
source of light. In the optical system used, this was the spheric
side of the lens, the other side being aspheric.
BRIEF SUMMARY OF DRAWINGS
Other features, objects and advantages of the invention will be
apparent from the following specification, taken in connection with
the accompanying drawings in which:
FIG. 1 is a graph of transmittance against wavelength for the
infrared filter and for the dichroic filter on the lens; and
FIG. 2 is a longitudinal section through the centerline of the
fixture.
DESCRIPTION OF SPECIFIC EMBODIMENTS
In FIG. 1, the dotted curve shows the transmission of the infrared
filter for visible light and is to be somewhat low in the blue
(400- 500 millimicrons), higher in the green and yellow (500-600
millimicrons), and low again in the red (600- 750 millimicrons).
This, in conjunction with the incandescent filament source,
produces a somewhat greenish light.
The full-line curve shows the transmission of the dichroic filter,
which is high in the blue, and low in the yellow and green, rising
somewhat toward the red.
Although only the visible transmissions of the filters are shown,
the transmission of the infrared filter drops to zero at about 900
millimicrons and continues there up to at least 2,700 millimicrons,
which was the limit of the measuring equipment.
Referring to FIG. 2, a cross sectional view of the medical and
dental fixture is shown. The major components comprise a main
housing canister 10, an optical system 12 located within the
canister and a flexible boot 14 affixed to the rear end of the
canister. The boot 14 covers and holds the electrical connections
for a lamp 16. The lamp, being one of the components of the optical
system of the fixture, is positioned within an ellipsoidal-shaped
reflector 18. The lamp and reflector produce an intense source
whose light is directed through a rectangular opening 24 centrally
located in a fixed light gate 20. A spacing rim 22 spaces the lamp
and reflector from the light gate so that an optimum amount of
light produced by the lamp 16 passes through the gate opening 24
and thence to an aspheric lens 26, and an exterior heat absorbing
cover glass 32.
The lens 26 and heat absorbing cover glass 32 are spaced from one
another and held by a circular bezel 30. This segment of the
optical system produces a very sharply defined rectangular light
pattern.
The optically clad glass rod 40 shown in FIG. 2 is made of a glass
rod probe with optically polished ends and encased within a metal
casing. One end of the rod 40 extends into the housing 10, and
passes through the reflector and terminates just short of the
envelope 51 of the lamp, and perpendicular to the axis of the
filament 50. The other end of the rod 40 extends outwardly from the
housing 10 and is connected to a flexible fiber optic conduit
comprised of a standard bundle of flexible glass fibers 44 in the
shape of a conduit having an approximately circular cross
section.
With this arrangement the rod 40 collects from the filament light
which travels over the conduit 44 to emerge at the light exit end
48.
The lens surface facing the source of light, that is, the back
surface 28 of the lens 26 is coated with a dichroic filter 9 which
transmits more blue light than green, and which also passes the
red. The filter can be made in the usual manner with successive
thin coats or layers of magnesium fluoride and zinc sulfide, each
about one-fourth wavelength thick, there being 9 coats of magnesium
fluoride and 10 coats of zinc sulfide in all. The coatings can be
applied by vacuum disposition in the usual manner.
* * * * *