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Title:
UNIFORM LIGHT TRANSMITTING, INFRARED ABSORBING AND REFLECTING MATERIALS AND ARTICLES
United States Patent 3591248
Abstract:
A light-transmitting article composed of a layer of transparent material having radiant heat-absorbing properties and arranged to be exposed to a principal source of heat radiation, and a protective layer of transparent material disposed adjacent that surface of the first-mentioned layer which is to face the principal source of heat radiation and capable of at least temporarily reflecting at least a portion of the radiant heat from such source which the first-mentioned layer is capable of absorbing so as to protect the article from damage due to excessive heat absorption.


Inventors:
Meunier, Gerard (Jumet, BE)
Leger, Lucien (Montigny-le-Tilleul, BE)
Lelong, Jose (Givry, BE)
Application Number:
04/866104
Publication Date:
07/06/1971
Filing Date:
10/07/1969
Assignee:
Glaverbel S. A. (Watermael-Boitsfort, BE)
Primary Class:
Other Classes:
359/589, 428/432
International Classes:
B32B17/10; B44F1/06; C03C1/10; C03C17/06; C03C17/23; C03C17/36; C03C27/12; E06B3/67; E06B7/28; G02B5/20; (IPC1-7): G02B5/20
Field of Search:
350/1,163--166
View Patent Images:
US Patent References:
3266370Electro-thermo-phototropic compositions and apparatusAugust 1966Marks et al.
3259016Tunable semiconductor optical modulatorJuly 1966Rosenblum
3208860Phototropic material and article made therefromSeptember 1965Armistead et al.
3202054Radiation filter with plural iridized metal oxide filmsAugust 1965Mochel
3192575Heat insulating windowJuly 1965Rosenau et al.
3078693Method and apparatus for producing filmed bent glass sheetsFebruary 1963Lytle
3069301Heat-reflecting laminatesDecember 1962Buckley et al.
2887010Neutral density filtersMay 1959Ruettiger
Other References:

Swarts, "Solar Control Through Glass" THE GLASS INDUSTRY, Vol. 45, No. 12, Dec., 1964 pp. 670--674 and 711..
Primary Examiner:
Schonberg, David
Assistant Examiner:
Kusmer, Toby H.
Claims:
We claim

1. A light-transmitting article for providing protection against infrared radiation emanating from a principal source, comprising, in combination:

2. An arrangement as defined in claim 1 wherein said first layer comprises a sheet of transparent material and a first transparent coating disposed on said sheet.

3. An arrangement as defined in claim 2 wherein said first coating is tinted.

4. An arrangement as defined in claim 3 wherein said first layer acquires a deeper tint as the radiation to which it is exposed increases.

5. An arrangement as defined in claim 2 wherein said first coating is substantially colorless when exposed to low intensity radiation and acquires a tint when exposed to high-intensity radiation.

6. An arrangement as defined in claim 2 wherein said second layer comprises a transparent sheet and a second coating disposed on said sheet.

7. An arrangement as defined in claim 1 wherein said first layer is tinted and absorbs thermal radiation under all ambient radiation conditions.

8. An arrangement as defined in claim 7 wherein said second layer is constituted by a coating disposed on one surface of said first layer.

9. An arrangement as defined in claim 7 wherein said second layer comprises a coating on a transparent sheet.

10. An arrangement as defined in claim 9 wherein said second layer is composed of a material selected from the group consisting of metals, metal containing compounds and metalloid containing compounds.

11. An arrangement as defined in claim 9 wherein said second layer is composed of an oxide.

12. An arrangement as defined in claim 9 wherein said second layer has an index of refraction which is different from that of the first layer.

13. An arrangement as defined in claim 12 wherein said second layer has a larger index of refraction than said first layer.

14. An arrangement as defined in claim 1 wherein said second layer is constituted by a film of titanium dioxide deposited on one surface of said first layer.

15. An arrangement as defined in claim 1 wherein said first layer is constituted by a glass sheet.

16. An arrangement as defined in claim 1 further comprising an additional sheet of transparent material, and wherein said first layer is constituted by a sheet of transparent material and said second layer is constituted by a coating disposed on one of said sheets.

17. An arrangement as defined in claim 16 wherein said second layer is disposed between said first layer and said additional sheet.

18. An arrangement as defined in claim 16 wherein said first layer is tinted and said additional sheet is substantially colorless.

19. An arrangement as defined in claim 18 wherein said second layer is deposited on said additional sheet.

20. An arrangement as defined in claim 16 wherein both said additional sheet and said first layer are tinted.

21. An arrangement as defined in claim 20 wherein said additional sheet has a tinting which is different from that of said first layer.

22. An arrangement as defined in claim 16 wherein said additional sheet is spaced from, and disposed parallel to, said first layer.

23. A light-transmitting article for providing protection against infrared radiation emanating from a principal source and permanently having a substantially uniform transmission characteristic over the visible light band, comprising, in combination:

24. An arrangement as defined in claim 23 wherein said first layer is constituted by a sheet of soda-lime glass containing a tinting agent constituted by at least one of the substances Fe2 O3, CoO, NiO, MnO and Se.

25. An arrangement as defined in claim 24 wherein any of said tinting agent substances contained in said soda-lime glass sheet are present in the following concentration:

26. A light-transmitting article for providing protection against infrared radiation emanating from a principal source and permanently having a substantially uniform transmission characteristic over the visible light band, said article consisting of:

Description:
The present invention relates to transparent solid materials and to articles incorporating such materials.

Among the many uses of transparent materials in sheet form, it is known to use materials of various colors in order to protect objects against light or heat radiation whose nature or intensity might be harmful or annoying. For example, dark blue panes are used by arc-welders, and building windows are often made of tinted glass to prevent the occupants from being exposed to excessive infrared radiation.

The radiant energy absorbed by these materials causes them to become heated and the amount of this heating is often unacceptably high, particularly when they are exposed to thermal radiation. For example, some tinted glass panes are liable to break or to damage their frame if the frame should become heated by conduction or if there should be an excessive amount of differential expansion between the pane and the frame. It is also evident that the heating of the glass by the energy which it absorbs is detrimental to its ability to provide protection against heat radiation since the heat stored in the glass tends to reradiate.

It is a primary object of the present invention to overcome these drawbacks.

Another object of the present invention is to at least partially insulate a layer of heat-absorbing material from the source of radiant heat.

Still another object of the present invention is to provide a layer of light-transmitting, radiant heat-reflecting material between a layer of light-transmitting, radiant heat-absorbing material and the source of radiant heat.

According to the present invention, these and other objects are achieved by the provision of a light-transmitting article for providing protection against radiant heat, which article is composed of at least two layers. The first of these layers is made of transparent material and is provided for absorbing radiant heat at least when subjected to the influence of radiant energy having a predetermined intensity level. The second layer, also of transparent material, is provided for at least temporarily reflecting radiant heat, the second layer being disposed between the first layer and the principal source of radiant heat to which the first layer is exposed.

As a result of this arrangement, the second layer of transparent material acts to shield the first layer of material from a substantial portion of the incident thermal radiation. The term "layer" employed herein is used broadly to cover both self-supporting layers or sheets and coating layers applied to other self-supporting sheets.

Mention has already been made of the damage which can result from the excessive exposure of colored transparent glass sheets to heat radiation. It should also be mentioned that several types of transparent coating layers can also be adversely affected by radiant heat. For example, some phototropic coating layers which are applied to window panes to reduce their transparency under conditions of strong sunlight function less efficiently when exposed to appreciable thermal radiation due to the fact that the layer becomes temporarily capable of absorbing radiation when exposed to intense sunlight to such an extent as to cause an increase in its temperature. This can be prevented by shielding such a coating layer from at least the major part of the incident thermal radiation according to the techniques of the present invention.

Comprehensively stated, embodiments of the present invention include any article having a first layer of transparent material which has, or which is capable of temporarily acquiring under the action of sufficiently intense radiant energy, radiant heat-absorbing properties, and a second layer of transparent material which has, or which is capable of temporarily acquiring, radiant heat-reflecting properties and which is disposed to shield the first layer from incident thermal radiation.

Since units produced according to the present invention are primarily intended for affording protection from solar radiation, the condition that the first layer, or layer to be protected, have, or be capable of acquiring, radiant heat-absorbing properties is satisfied if, under the action of heat radiation or of intense sunlight, the layer becomes capable of absorbing a significant proportion of the incident thermal radiation. In order for the second layer, or protecting layer, to satisfy the condition of having, or of being capable of acquiring radiant heat-reflecting properties, it is not necessary that this layer be capable of reflecting all of the incident heat radiation. It is only necessary that this layer be capable of reflecting a significant proportion of the incident radiation, and not just an incidental proportion such as may be reflected by the protected layer itself. It is preferable for the permanent or temporary radiant heat-reflecting properties of the protecting layer to be as good as possible, and in general, this layer should be capable of reflecting at least the major part of the incident solar thermal radiation.

The material used for the layers according to the present invention may also be of the type which normally possesses thermal radiation absorbing or reflecting properties to some degree, but which possesses these properties in a greater degree under certain conditions, such as when subjected to strong sunlight or to an electric field, for example.

If the material or article incorporates a protecting layer at only one side of a layer or layers to be protected then care must be taken when the material or article is used to ensure that the protecting layer is located between the layer or layers to be protected and the source of potentially harmful thermal radiation.

The primary intended field of use of the invention is the field of windows comprising a transparent pane or panes or one at least of which is colored and/or bears a phototropic layer which acquires coloration or a deeper coloration than normal when exposed to strong sunlight. Such windows are often used when it is desired to shield the interior of a building from strong sunlight. The advantage of providing a phototropic layer is that the layer can be constituted so as not materially to reduce the transparency of the window to light when the prevailing daylight is weak.

A material or article according to the invention may incorporate one or more light-transmitting sheets of plastic composition, e.g., plastics sold under the trademarks of "Perspex" or "Plexiglass," acetate or acrylic resins, and vinyl resins, and such sheet or sheets may be rigid or flexible. However, the invention is more particularly concerned with materials and articles comprising sheet glass.

In spheres of use of colored light-transmitting materials in which the degree of coloration has hitherto been selected not only with a view to the required light filtration, but also with a view to reducing the amount of transmitted thermal radiation the invention has the advantage of permitting a greater freedom of choice as regards the color of the material. As the colored material is at least to some extent relieved of its function of affording protection against thermal radiation, the color can in any given case by chosen to be paler or more pleasing.

By using a radiant heat-reflecting coating layer in association with a light-transmitting sheet having a dominant tint complementary to that of the light transmitted by such layer in daylight, a material can be prepared which has a neutral tint or a tint approaching neutral. Such a material is of potential value for glazing buildings in which it is desirable for objects to be seen in their natural colors, e.g., for buildings in which textile materials for decorative or clothing purposes are exhibited.

Additional objects and advantages of the present invention will become apparent upon consideration of the following description when taken in conjunction with the accompanying drawings in which:

FIG. 1 is a side, cross-sectional view showing a first embodiment of the present invention.

FIG. 2 is a side, cross-sectional view showing another embodiment of the present invention.

FIG. 3 is a partly cutaway, perspective view of the unit shown in FIG. 2.

FIG. 4 is a side, cross-sectional view of yet another embodiment of the present invention.

FIG. 5 is a side, cross-sectional view of still another embodiment of the present invention.

FIG. 6 is a side, cross-sectional view showing of a further embodiment of the present invention.

FIG. 7 is a side, cross-sectional view showing another further embodiment of the present invention.

The unit shown in FIG. 1 includes a tinted glass sheet 1 coated on one side with a transparent radiant heat-reflecting film 2. The sheet 1 is preferably made of an athermanous soda-lime containing a high proportion of iron oxide to give it a blue-green tint.

According to one preferred embodiment, the glass sheet 1 is a soda-lime glass which has incorporated therein at least one of the following substances as a coloring agent: Fe2 03, Co0, Ni0, MnO, or Se, in order to give to the unit a neutral tint or a tint approaching neutral.

However, any of these coloring agents can be used individually or in combination of two or materials. The use of a single substance will only permit, in general, an imperfect neutral tint to be attained. However, by combining two or more of the above substances in appropriate concentrations, it is possible to create a tint having an excellent neutral light transmission characteristic. The choice of one or another of these materials in any case depends on the purpose which the transparent article is to serve.

Preferably, the above-mentioned tinting substances should be used, whether singly or in combination of two or more, in the following concentrations:

Fe2 03 from 0.01 to 0.15 percent

CoO from 0.0001 to 0.01 percent

NiO from 0.02 to 0.05 percent

MnO from 0.01 to 0.5 percent

Se from 0.005 to 0.03 percent

The composition of the layer 2 must be selected to ensure adequate adherence to the surface by which it is carried, and so that it can form a thin film which will not be impaired by exposure under the intended conditions for use.

For forming an inherent radiant heat-reflecting film, while any substance which has these properties and has the requisite radiant heat-reflecting properties can be used, it is in general preferred to use a metal or metal containing film. Such films generally show good ultraviolet and infrared ray-reflecting properties. Also compounds of various metalloids can be used. Oxide coatings have the advantage that they are in general very resistant to abrasion.

A metal which is very appropriate for forming a film on glass is gold. A preferred metal oxide for forming a radiant heat reflecting film is titanium oxide which is easy to deposit and which adheres very well to glass surfaces.

It is recommended to employ for the formation of a radiant heat-reflecting coating layer, a material of which the refractive index is different from, and preferably higher than, that of the material on which the layer is deposited so as to promote good reflection of radiant heat rays at both surfaces of the layer. Titanium dioxide has a high refractive index, appreciably in excess of 2, which is another factor in its favor. This material may be readily deposited on glass sheet 1 by any one of the known processes, such as by hydrolyzing titanium chloride. It is also recommended that the optical thickness of the transparent radiant heat-reflecting film have a value equal to a quarter of one of the wavelengths of the thermal radiation to which the material is to be exposed, or equal to an odd numbered multiple of such a value. This ensures a very strong reflection of rays whose wavelengths are equal or close to such one wavelength, so that the thermal rays will be reflected more strongly than the light rays.

For example, when, as is normally the case, it is desired to cause a high percentage of the heat energy to be reflected, the above-mentioned interference phenomena are brought into play by giving the oxide film an optical thickness which is equal to a quarter, or an odd numbered multiple of a quarter, of a selected wavelength in the infrared band. As a result, the radiation wavelengths in the vicinity of the selected wavelength are more intensively reflected. In this case, the selected wavelength normally lies between 1 and 1.2 μ, which corresponds with a wavelength region in which the solar heat energy is relatively intense.

The product which has just been described can be advantageously used for glazing buildings. It is inexpensive and affords a high standard of thermal comfort, as well as effectively protecting the eyes against solar glare.

Turning now to FIGS. 2 and 3, there is shown a laminated, multilayer pane one outer layer of which is constituted by a sheet 3 of blue glass whose tint is created by the addition of Co0 to glass. The other outer layer of the pane is constituted by a sheet 4 of transparent glass. Between the sheets 3 and 4 are disposed an intervening layer 5 polyvinylbutyral and a silver film 6 which is sufficiently thin to pass an appreciable portion of the incident light. Such a laminated pane is particularly suitable for use as an inspection window in furnaces and for welders' spectacles and helmets. The pane is arranged in use so that the radiation to be reflected and absorbed strikes the film 6 before reaching the sheet 3.

The arrangement shown in FIGS. 2 and 3 can also be constructed by omitting the bonding layer 5 and by soldering the sheets together along their edges. If both the sheets 3 and 4 are tinted, the composition of one of the sheets will in general have to be such that it does not absorb thermal radiation to any appreciable extent unless the outer surface of this one sheet is coated with a protecting, heat-reflecting layer. When two sheets are employed, the tint of one of them can be selected, for example, so as to vary the overall tint of the pane in a predetermined manner, or so as to selectively absorb radiation in a predetermined wavelength band.

Turning now to FIG. 4 there is shown another embodiment according to the present invention in the form of a double pane composed of the sheets 7 and 9 separated from each other by a space 13. The sheet 7 is made of gray tinted glass and has its inner surface coated with a thin gold film 8. The edges of the inner surfaces of sheets 7 and 9 have copper bands 11 and 12, respectively, deposited thereon and these copper bands are connected together by a metal strip 10 which is soldered to both bands. The sealed space 13 is preferably filled with a dry gas.

Such an arrangement is particularly advantageous for use in homes because it combines the beneficial features of a double pane with the improvements resulting from the present invention.

As is well known, a thin gold layer, such as the layer 8, has the property of reflecting thermal radiation more intensely than it does light radiation. In addition, it is possible to accurately control the proportion of light transmitted by properly selecting the composition of the gray tinted glass sheet 7. Instead of having a gray tint, the sheet 7 may be given a dominant tint which is complementary to that of the film 8 so that the overall tint imparted to light by the arrangement 7, 8 will be substantially neutral.

Although the sheet 9 may be made of colorless glass, it is also possible to make this sheet of a glass which is slightly tinted to have a tint which is complementary to that of the film 8 or which harmonizes particularly well with the colors of the building facade.

In the arrangement in FIG. 4, the sheet 9 will only be heated to a small degree because its tinting is of such a nature that it will not absorb any substantial amount of thermal radiation.

The arrangement shown in FIG. 4 can also be constructed to have a colorless glass sheet constituting the sheet 7 and a suitably tinted glass sheet for the sheet 9, with the arrangement being installed so that sheet 7 is disposed to the outside of the building. The sheet 9 may be given a dominant tint which is complementary to that of the film 8 so that the assembly imparts a neutral tint to the light passing therethrough. For example, the gold film 8 will have a gray-green color when interposed between the viewer and sunlight and a tinted glass sheet 9 having an appropriate complementary dominant tint may be fabricated from a conventional soda-lime glass composition to which 0.0065 percent Co0 has been added. A double-pane unit constructed from these materials has a transmission coefficient of the order of 40 percent for waves having a wavelength between 0.4 and 0.6 μ and a transmission coefficient of approximately 33 percent for waves having a wavelength between 0.6 and 0.75 μ.

A dominant tint substantially complementary to that of the gold film can also be produced by fabricating the soda-lime glass to have 0.0065 percent Co0 and 0.0133 percent Se. A double pane made of these materials exhibits an almost uniform transmission of light in the visible range, the transmitted light being subjected to a substantially neutral tinting. It is also possible to obtain a good neutral tint by using a colored glass prepared by adding to a soda-lime mass of ordinary composition a mixture of Ni0 and Co0, or a mixture of Fe2 03 and Ni0, or a mixture of Fe2 03 and Co0, or a mixture of Co0, Fe2 03 and Ni0.

A modification of the arrangement shown in FIG. 4 is shown in FIG. 5 to include a gray-tinted glass sheet 14 and a spaced glass sheet 15 assembled with the sheet 14 by means of bands 11 and 12 and strip 10 in a manner similar to that for the arrangement of FIG. 4. A film 16 of titanium oxide is deposited on the outer surface 17 of sheet 15, this being the surface which is exposed to the radiation to be absorbed. The sheet 15 may either be tinted or untinted. The arrangement shown in FIG. 5 has the advantage that the radiant heat-reflecting film 16 is positioned to protect both of the glass sheets 14 and 15, thus permitting a wider range of possible tints to be imparted to sheet 15. It should be noted that when a transparent film, such as the film 8 of FIG. 4 or the film 16 of FIG. 5, is applied to a colorless glass sheet, it is easier to inspect the film to assure that it has the desired properties than when this film is applied to a tinted sheet.

While arrangements which employ a tinted sheet coated with a transparent radiant heat-reflecting layer effectively reduce the transmitted thermal radiations, they do have the drawback that the tinted material reduces the intensity of the transmitted light by a substantially constant percentage irrespective of the intensity level of the incident light. As a result, the level of illumination within the building can become so poor during periods of weak sunlight that the use of artificial becomes necessary in cases where artificial light would not be needed if the building were furnished with ordinary colorless windows. In order to eliminate this disadvantage, and in further accordance with the present invention, the window panes can be provided with at least one phototropic layer. Such a layer permits the illumination level within the building to be maintained at a substantially constant level despite relatively large fluctuations in the intensity level of the incident sunlight.

Such a phototropic layer may be arranged for reducing the light transparency of the material when the incident light intensity is high, this layer being shielded by a radiant heat-reflecting layer from thermal radiation which might reduce its efficiency. The phototropic layer can also be arranged to reflect a portion of the incident light and much of the thermal radiation under conditions of high intensity incident light. This layer may be so constituted that its light-transmitting properties are varied automatically under the action, either direct or indirect, of the incident light.

For example, a phototropic layer may be composed of a material, which, when exposed to sufficient light or heat, reversibly crystallizes to some degree so that its coefficient of reflection is modified. One such material is calcium butyrate incorporated in an agar binder. If such a phototropic layer is used on a colored light-transmitting sheet, any heating of the colored sheet directly participates in increasing the reflecting property of the phototropic layer.

As another example a protecting layer may be in the form of a thin metallic or semiconductive layer whose radiation-reflecting property is varied by the application of an electric field. The intensity of this field may itself be controlled by sunlight through the agency of a photoelectric cell, or by a thermostatic cell.

As yet another example, a material or article according to the invention may comprise a phototropic substance of which the light transmission varies automatically under the action of variations in the intensity of incident light, so as to afford an illumination level in the interior of a room which is substantially constant, for example. Such a phototropic substance may be provided for example, between two sheets of glass or plastic material or may be in the form of a thin transparent coating layer or film which is applied to a sheet of glass or other light-transmitting material (which may be colorless) and whose nature and thickness are chosen in order to preserve a sufficient interior illumination level during periods of feeble sunlight, the phototropic layer functioning to reduce the light transmission during periods of strong sunlight. The transformation of the light-transmitting properties of such a phototropic layer may occur, for example, under the action of variations in the intensity of the incident sunlight or under the action of such heat rays as penetrate to such layer through a protecting radiant heat-reflecting layer.

Phototropic layers with variable light transmission coefficients include layers of organic phototropic substances, for example substances which pass reversibly from a sol to a gel state with accompanying change of transparency, or of color, under the action of heat radiation. Such substances are for example: polyvinyl methyl ether, alkaline earth metal salts of polyacrylic acid, and polymerized polyvinyl partial acetals or cetals having the ether oxygen atoms associated with water or hydrated salts.

A material or article according to the invention may equally well comprise a phototropic layer comprising a compound, or compounds, which reversibly dissociates under the action of light, one of the elements of dissociation becoming absorbed reversibly on a support and being subsequently released when the exciting light radiation is reduced or terminated, while the other element restricts the passage of visible light and heat rays. Such compounds are for example light-sensitive halogenides to which are added catalysts such as copper halogenides, cadmium halogenides or nickel halogenides.

One arrangement of the above-described type may be constructed to have the form shown in FIG. 6. According to this form of construction, the sheet 18 is made of an athermanous soda-lime glass containing between 1 and 2 percent Fe0. The film 19 is composed of four successively applied layers constituted by: a first layer 20 of silver having a thickness of 100 A; a second layer 21 of Si0 having a thickness of 2 μ; a third layer 22 of SnO2 having a thickness of 3 μ and containing selenium in such a concentration that the ratio of selenium atoms to tin atoms is 1:100; and a final layer 23 of silver having a thickness of 100 A. These successive films are preferably applied to the glass sheet 18 by evaporation in a vacuum. In the resulting composite sheet, the SnO2 layer constitutes a layer having a variable reflection coefficient. In use, the reflection coefficient of this layer is caused to vary by varying the potential of an electric field applied across it between the two silver layers, which constitute electrodes, and the voltage between these silver layers is preferably controlled by a photoelectrical cell 24. The SiO layer is provided as an insulating layer which prevents the passage of current through the SnO2 layer between the silver layers.

After the installation of such a pane, the photoelectric cell is placed so as to be exposed to the prevailing sunlight. When the light is feeble, the voltage across the SnO2 layer will assume a value such that the layer will only reflect a small percentage of the visible light and thermal radiation. Under these lighting conditions, the athermanous glass sheet can readily absorb the low intensity heat rays without becoming unduly heated, so that there is no risk of breakage of the glass under these conditions.

On the other hand, when the sunlight is very strong, the photoelectric cell will apply a potential between the silver electrodes whose value is such as to give the SnO2 layer a high heat-reflecting coefficient. In fact, this layer can be made to reflect all of the incident infrared radiation, together with a small percentage of the visible light. The athermanous glass sheet can absorb any small residual heat radiation not reflected by the SnO2 film without becoming unduly heated.

Another form of construction according to the present invention will have the form shown in FIG. 7. According to this form of construction, the first glass sheet 25 is constituted by a colorless sheet carrying a gold film 26 having a thickness of 150 A and having a high coefficient of reflection with respect to thermal radiation. The thickness of this film is such that even in periods of weak sunlight a sufficient level of illumination will be maintained within the building. In place of the uncoated glass sheet 14 of FIG. 5, a sheet 27 of soda-lime glass coated with a 200 A thick transparent layer 28 of a mixture of 50 percent AgCl and 50 percent AgBr is employed. This silver halide layer is in turn coated with a layer 29 of SiO 500 A thick and then with a protective impermeable calcium silicate layer 30.

Under weak lighting conditions, only the gold film on sheet 25 acts to reduce the intensity of the transmitted light. The silver halide phototropic layer remains inactive and practically colorless. As the intensity of the sunlight increases, the gold film continues to reflect the same proportion of incident light radiation and effectively reflects most of the radiation in the infrared region. At the same time, the silver chloride and silver bromide decompose and the liberated bromine and chlorine are absorbed reversibly by the SiO layer. As a result, the composite pane becomes more opaque and prevents the transmission of a greater portion of the visible radiation, as well as the remainder of the heat radiation, while imparting a neutral tint to the transmitted light. The level of illumination in the room is thus maintained substantially constant at a comfortable level, while the thermal radiation is substantially entirely reflected or absorbed.

It may thus be seen that the present invention provides arrangements in which one layer of material effectively reflects a large portion of the incident thermal radiation, while another layer absorbs the residual thermal radiation passing through the protecting layer. It may also be seen that such protecting layer may be a layer which permanently reflects thermal radiation or which only temporarily reflects this radiation under certain conditions. For example, the layer may be of a type associated with means for creating or intensifying an electric field which serves to reduce the transparency of the layer of thermal radiation.

It should also be noted that the present invention can be applied to the manufacture of sheet materials comprising a single transparent sheet having radiant heat-absorbing properties and coated with one or more transparent protecting layers, or to the manufacture of laminated sheets comprising two or more transparent sheets bonded together and one or more coating layers applied between the sheets or on the outer surface of one or both of them.

It should further be noted that the present invention is concerned not only with sheet materials as such, but also with articles, such as windows, incorporating a transparent layer which has or which under certain conditions acquires, thermal radiation absorbing properties, and which is protected by a protecting layer which is, or which becomes under certain conditions, radiant heat reflecting. In such manufactured articles, such as multipane units, there may be provided separate transparent sheets held in a frame and spaced apart from one another, with one sheet or a coating layer thereon being provided to protect the other sheet, or to protect a coating layer thereon, against the thermal radiation.

It will be understood the above description of the present invention is susceptible to various modifications, changes, and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.