Note: Descriptions are shown in the official language in which they were submitted.
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Solar Protective Filter
Field of the Invention
The invention relates to a solar protective filter for
protecting the eye against damaging and disturbing radiation.
Back~round of the Invention
Such solar protective filters are utilized in solar
protective spectacles and serve to absorb as completely as
possible radiation from the ultraviolet spectral range and to
limit to a minimum amount the danger of glare from rays from
the visible spectral range. However, the filter
characteristic mus~ be so designed that the so-called
signal~light recognition is assured. According to the
requirements of the ISO "Specification for afocal filters for
daylight`' (8/87), this means that light from the
green-yellow-red spectral range may be attenuated to at
mos~ 80~. Pursuant to a standardization (different in various
parts of the world~, the recognition of blue light (for
example, of police vehicles and of rescue vehicles3 must be
possible.
Solar protective filters are made of glass or of a
transparent plastic, for example, the plastic available under
the trade designation CR 39O This material can be d~ed as a
mass, however, a coating determining the spectral transmission
is for the most part applied to the base material. This
coating can comprise thin vapor-deposited interference films.
The coating can however be produced for filters made of
plastic also by dipping in a dye bath. Dye molecules then
lodge in the layers of the plastic near the surface. The
spectral transmission of such protective filters made of
plastic is then determined solely by the spectral absorption
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of the applied dye coating.
The coefficient of absorption or transmission for solar
protective filters is determined by means of convolution with
the photopic solar response curve (V~ - curve) which is
determined by standardization. As a practical matter, such
filters having an absorption of 85%, 65% to approximately 40%
are available.
The solar protective filters known up to now essentially
have a transmission T~ of 0 fox xadiation of the
wavelength ~ < 350 nm. Thereafter, the transmission increases
quasi linearly with increasing wavelength and remains
approximately constant at a maximum value in the
range 450 < ~ < 780 nm. In general, the transmission also
still remains constant for ~ > 780 nm up to more than 800 nm
and only again becomes less thereafter, mostly caused by the
absorption of the filter material in the IR-range.
It has been shown that these known solar protective
spectacles negatively influence the contrast sensitivity
especially at low luminance and that under specific light
conditions, for example for hazy weather or for indirect
illumination, a disturbing blurred luminance occurs. This
disadvantage has a negative effect on the acceptance of such
protective spectacles.
Summary of the Invention
~5 It is an object of the invention to provide a solar
protective filter to protect the eye against damaging and
disturbing radiation which is characterized by a greatly
improved contrast sensitivity. This increase of the contrast
sensitivity should, above all, have an effect for average
luminance and for unfavorable lighting conditions.
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According to a feature of the invention, this object is
achieved by means of a solar protective filter whose spectral
distribution of the transmission (T~) is configured in
dependence upon the wavelength (~) of the incident radiation
according to the following:
~a) T~ ~ 1% in the range ~ < 350 nm;
(b) T~ < 20% in the range 350 < ~ < 400 nm;
(c) 5 < T~ < 30~ in the rang~ 400 < ~ < 500 nm; and,
(d) T~ increasing approximately linearly with ~ in the range
of 500 ~ ~ < 780 nm starting from the value for T500.
As can be recognized from these features, the
transmission for the shortwave component of the radiation is
significantly reduced in the solar protective filter according
to the invention. In this way, and in a surprising manner, a
significant increase of the contrast sensitivity is obtained
and an improved acceptance and compatibility of the solar
protective filters result. The increase of the contrast
sensitivity (as investigations in connection with the
invention have shown) can be accounted for by the fact that
the ocular media sca~ter in the shortwave range of the light
and that this scatter leads to glare phenomenon and
disturbances. An especially significant attenuation of this
solar range has a positive effect on the contrast sensitivity.
For shortwave light, an interaction furthermore occurs between
the photopic system and the scotopic system of the eye which
especially for medium and low luminance leads to a
deterioration of the contrast sensitivity.
~ ith the solar protective filter according to the
invention, the contrast sensitivity with respect to known
filters and especially also the contrast sensitivity with
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medi~m luminance is improved.
A solar protective filter configured according to the
invention has a red brown tint according to a preferred
embodiment. Even when such a filter is configured with an
absorption of 80 to 85% determined in the usual manner by
convolution with the V~ - curve, it has nonetheless the
subjective effect for the user as does a neutral grey filter
having an absorption of 50%. From this it is apparent that a
sGlar protective filter configured pursuant to the invention
is very comfortable to wear for the user. The solar
protective filter according to the invention falsifies the
colors for the user by only a small amount and fulfills all
requirements with reference to the signal-light recognition
according to ISO "Specification for afocal filters for
daylight", test pursuant to method ~.
In a solar protective filter configured according to
another feature of the invention, the shortwave component of
the light is still further reduced in that the transmission
for wavelengths up to 380 nm is reduced to values < 1%.
Another advantageous embodiment of the solar protective
filter according to the invention provides that the
transmission for wavelengths above the visible range, that is
for ~ > 780 nm, is reduced to values < 1~. In this way, the
eye is protected also against radiation from the shortwave
infrared range. In addition, materials are disclosed for the
solar protective filter as is the nature of the configuration
of the spectral transmission.
Brief Description oE the Drawin~s
The invention will now be described with reference to the
drawings wherein:
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FIG. l shows the spectral transmission of a solar
protective filter according to the invention and configured
pursuant to a first embodiment;
FIG. 2 shows the spectral transmission for a second
embodiment; and,
FIG. 3 shows the international spectral brightness curve
(V~ - curve).
Description of the Preferred Embodiments of the Invention
In the embodiment of FIG. 1, the solar protective filter
has a transmission < 1~ for wavelengths ~ < 380 nm, that is it
absorbs the UV-radiation lying in this range almost completely.
Above A = 380 nm and up to approximately ~ = 400 nm, the
spectral transmission (T~) increases rapidly to a value of
approximately 15%. This value remains approximately constant
up to ~ = 500 nm so that the recognition for signal lights
according to ISO "Specification for afocal filters for
daylight", test according to method B, is guaranteed.
Above ~ = 500 nm, the transmission increases to its highest
value starting from the value for T500 preferably linearly
with the wavelength (A~. The linear increase shown is
idealized and an actual linear increase can hardly be
achieved. The increase should however be as linear as
possible in order to prevent color falsifications by means of
the solar protective filter.
The maximum value of the transmission T~ is attained at,
for example, ~ ~ 700 nm. This value remains approximately
constant up to the end of the visible range at ~ = 7B0 nm and
then drops to values < 1~ up to approximately ~ = 820 nm.
Such a course of the spectral transmission can be
~30 obtained for solar protective filters of glass by coating with
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thin interference coatings. In this connection, it is
possible to apply the coatings which fulfill different tasks
to both sides of the solar protective filter. Such coatings
can today be calculable with respect to their composition so
that a predetermined course of the T~ - curve is obtained and
the production of such coatin~s is possible in
computer-controlled vaporization units.
Protective filters of plastic can also be coated in this
manner. However, for filters made of plastic, it is more
economical to obtain the spectral transmission by dipping into
an appropriate dye bath. The dye molecules become lodged in
the layers of the filter close to the surface. It is also
possible to control the dye process so that the filter is dyed
throughout. In this way, the UV-stability of the filter is
improved.
The suitable composition of the dye bath can be
determined by means of computation or experimentation with
so-called dispersion dye materials being used.
A solar protective filter of FIG. 1 has an absorption of
approximately 65 to 85%. This absorption is in a known manner
determined through convolution with the V~ - curve shown in
FIG. 3. Nonetheless, this protective filter acts subjectivaly
as a neutral grey filter with 50% absorption for the wearer
thereof. The wearer enjoys a very good contrast sensitivity
even for mid and low luminance without the occurrence of a
disturbing color falsification of the observed scene.
In the embodiment of FIG. 2, the transmission is reduced
to values < 1% for wavelengths ~ < 400 nm and then increases
and reaches a value of approximately 12% in the
range 410 < ~ < 500 nm. Thereafter, the spectral transmission
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increases with the wavelength substantially linearly and
reaches its maximum value at approximately ~ = 780 nm which it
maintains also for ~ > 780 nm. Above ~ = 800 nm, that is in
the IR-range, the transmission drops again because of reduced
IR-transmission of the filter material.
The spectral transmission curve shown in FIGS. 1 and 2
are only examples which serve to show the principle course of
this curve.
It is understood that the foregoing description is that
of the preferred embodiments of the invention and that various
changes and modifications may be made thereto without
departing from the spirit and scope of the invention as
defined in the appended claims.
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