GB2265471A - Photochromic filter assemblies - Google Patents
Photochromic filter assemblies Download PDFInfo
- Publication number
- GB2265471A GB2265471A GB9306104A GB9306104A GB2265471A GB 2265471 A GB2265471 A GB 2265471A GB 9306104 A GB9306104 A GB 9306104A GB 9306104 A GB9306104 A GB 9306104A GB 2265471 A GB2265471 A GB 2265471A
- Authority
- GB
- United Kingdom
- Prior art keywords
- filter
- filters
- wavelengths
- incident
- photochromic
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
Classifications
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
- A61F9/00—Methods or devices for treatment of the eyes; Devices for putting-in contact lenses; Devices to correct squinting; Apparatus to guide the blind; Protective devices for the eyes, carried on the body or in the hand
- A61F9/02—Goggles
- A61F9/022—Use of special optical filters, e.g. multiple layers, filters for protection against laser light or light from nuclear explosions, screens with different filter properties on different parts of the screen; Rotating slit-discs
- A61F9/023—Use of special optical filters, e.g. multiple layers, filters for protection against laser light or light from nuclear explosions, screens with different filter properties on different parts of the screen; Rotating slit-discs with variable transmission, e.g. photochromic
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B5/00—Optical elements other than lenses
- G02B5/20—Filters
- G02B5/22—Absorbing filters
- G02B5/23—Photochromic filters
-
- G—PHYSICS
- G02—OPTICS
- G02C—SPECTACLES; SUNGLASSES OR GOGGLES INSOFAR AS THEY HAVE THE SAME FEATURES AS SPECTACLES; CONTACT LENSES
- G02C7/00—Optical parts
- G02C7/10—Filters, e.g. for facilitating adaptation of the eyes to the dark; Sunglasses
- G02C7/102—Photochromic filters
-
- G—PHYSICS
- G02—OPTICS
- G02C—SPECTACLES; SUNGLASSES OR GOGGLES INSOFAR AS THEY HAVE THE SAME FEATURES AS SPECTACLES; CONTACT LENSES
- G02C7/00—Optical parts
- G02C7/14—Mirrors; Prisms
Landscapes
- Health & Medical Sciences (AREA)
- Physics & Mathematics (AREA)
- Ophthalmology & Optometry (AREA)
- Optics & Photonics (AREA)
- General Health & Medical Sciences (AREA)
- General Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Biomedical Technology (AREA)
- Heart & Thoracic Surgery (AREA)
- Vascular Medicine (AREA)
- Life Sciences & Earth Sciences (AREA)
- Animal Behavior & Ethology (AREA)
- Public Health (AREA)
- Veterinary Medicine (AREA)
- Optical Filters (AREA)
Abstract
An optical device 10 (e.g. a human eye) is protected from very high levels of illumination 12 by photochromic filters 11A, 11B, etc which progressively attenuate the transmitted visible light. The filters are activated by the UV content of the illumination which is intercepted by a 50% UV beamsplitter 13 to permit the front faces of the filters to be irradiated by UV light whilst their rear faces are similarly irradiated by UV light directed by the beamsplitters, a fold mirror 14 and one or more UV bcamsplitters 13B, 13C, etc. Each filter is of limited thickness for maximum efficiency being equal to the penetration depth for the UV activation wavelengths. In other embodiments one or more double-sided filters is used. <IMAGE>
Description
PHOTOCHROMIC FILTER ASSEMBLIES
This invention relates to optics and to photochromic filter assemblies in particular.
Photochromic filters are already known and when exposed to wavelengths within an activation waveband they become less transmissive than previously to wavelengths within a transmission waveband. Typically the activation waveband is blue and ultra-violet light whilst the transmissive waveband is the visible spectrum which, when the filter is activated, can have an attenuation level of more than 99%. One known form of photochromic filter comprises a dispersion of photochromic materials or dyes in a carrier medium such as polyurethane.
Photochromic filters have already been proposed for use in protecting sensitive optical devices such as the human eye from saturation illumination levels such as occur with nuclear flash exposure. However, the known filters fail to get sufficiently dark when exposed to very high illumination levels and the resulting protection is inadequate.
We have now determined that the principal limiting factor in the performance of photochromic filters under high illumination levels is that the activation wavelengths are absorbed by those photochromic materials of the filter which are adjacent the surface of incidence of the illumination. This continues even after this layer of material has fully darkened. This creates a limited penetration depth (D) for activation wavelengths and the performance of the filter cannot be improved either by making the filter thicker or by increasing the concentration of the photochromic materials in the filter.
It is an object of the present invention to provide a new and improved method of protecting an optical device from high illumination levels. A further object is the provision of photochromic filter assemblies for use in the method.
According to one aspect of the present invention there is provided a method of protecting an optical device from high illumination levels comprising mounting in front of the device a plurality of photochromic filters and directing actuation wavelengths from the incident illumination to be incident on a face of each filter sufficient to activate each filter to the saturation level.
Preferably each filter has# a thickness substantially equal to the penetration depth D.
Preferably two of said filters are disposed back-to-back and conjoined to form a single element, the actuation wavelengths being directed to be incident on each of the exposed faces of the element.
The present invention also provides a photochromic filter assembly comprising a plurality of photochromic filters and means for directing actuation wavelengths from incident illumination to be incident on a face of each filter sufficient to activate each filter to the saturation level.
Conveniently said directing means comprises an ultra-violet beamsplitter.
Preferably each filter has a thickness substantially equal to the penetration depth D. Preferably two of said filters are disposed back-to-back and conjoined to form a single element, the directing means being arranged to direct the actuation wavelengths onto each of the exposed faces of the element.
The assembly may be incorporated in a pair of goggles for human wear to protect the eyes of the wearer from nuclear flash exposure.
According to another aspect the present invention provides a method of protecting from high illumination levels an optical device having a predetermined aperture, comprising expanding the incident beam,intercepting the expanded beam with a photochromic filter, and thereafter diminishing the beam size for reception by the aperture of the device, the filter having an area which is sufficiently large to provide protection by functioning at or below its saturation level and being activated by wavelengths contained in the expanded beam.
Embodiments of the present invention will now be described with reference to the accompanying drawings in which:- Fig. 1 schematically illustrates a first embodiment;
Fig. 2 shows a modification of the Fig. 1 embodiment;
Fig. 3 illustrates a second embodiment;
Fig. 4 shows a modification of the Fig. 3 embodiment and;
Fig. 5 schematically illustrates a further embodiment.
The embodiment which is shown in Fig. 1 for protecting an optical device 10 from exposure to very high levels of illumination such as arise from nuclear flash comprises providing in front of device 10 a plurality of photochromic filters llA,llB,llC,llD such that the visible light content of the incident illumination 12 passes through all of the filters and is progressively attenuated by each. This is achieved in this embodiment by locating a first beamsplitter 13A before the first filter llA.
Beamsplitter 13A is fully transmissive to visible light wavelengths but only partly, say 50%, transmissive to actuation wavelengths (UV/blue) so that 50% of the actuation wavelengths contained in the incident illumination 12 is incident on the front face of filter 11A causing it to reach saturation level. The diverted actuation wavelengths are directed by a reflector 14 to successive 50% beamsplitters 13B,13C,13D which are respectively angled to direct actuation wavelengths onto the rear faces of filters llB,llC,llD causing each to reach saturation level. The cumulative effect of each filter 11 provides maximum attenuation of the visible wavelengths prior to reaching device 10. Although each filter 11 can have any thickness, for maximum efficiency each should be substantially equal to the penetration depth D since this is both optically and cost efficient.
A UV/blue edge filter 15 is positioned immediately in front of the device 10 to prevent transmission of these wavelengths to the device 10 and this has the additional effect of redirecting these wavelengths to the near face of filter 11D to enhance the actuation thereof.
In the Fig. 2 embodiment filters 11A and 11B are arranged back-to-back and physically conjoined to form a single element 16 which for maximum efficiency should have a thickness only twice that of the penetration depth D.
Otherwise the Fig. 2 embodiment works in the same way as
Fig. 1 but with fewer components.
Figs. 3 and 4 illustrate arrangements which avoid the use of a primary beamsplitter 13A directly in front of the first filter 11A. This is achieved by utilising the illumination falling in the area peripherally surrounding the first filter 11A and directing that illumination or at least its Uv/blue content onto the second filter llB.
In Fig. 3 the second filter llB is conjoined with the first filter llA and the single filter element 16 is peripherally surrounded by an annular element 17 which is non transmitting to visible light but transmitting to UV wavelengths. A frusto-conical W reflector 18 directs the UV wavelengths onto the rear face of the filter element 16.
In Fig. 4 the first and second filters llA,llB are conjoined to form a single element 16 and a third filter llC is provided. The annular element 19 surrounding element 16 is both non-transmitting to visible light and has a 50% W beamsplitter 19A providing illumination to the rear face of element 16. A frusto-conical UV reflector 20 directs the remaining W wavelengths onto the rear face of filter 1lC.
In Fig. 5 the filter 11 is disposed in a region where the size of the illuminating beam 21 is expanded with respect to that of the initial illumination 12, the area of the filter 11 being sufficiently large to provide protection for the optical device 10 by functioning at or below its saturation level. The degree of expansion is determined from the ratio of maximum anticipated illumination to saturation level illumination. Expansion is provided by a beam expander 22. The output from the filter 11 is diminished by a beam contractor 23 for reception by the aperture 10A of the device. The filter 11 is activated by wavelengths contained in the expanded beam 21 and incident directly on the face of the filter.
Claims (9)
1. A method of protecting an optical device from high illumination levels comprises mounting in front of the device a plurality of photochromic filters and directing actuation wavelengths from the incident illumination to be incident on a face of each filter sufficient to activate each filter to the saturation level.
2. The method as claimed in Claim 1, wherein each filter has a thickness substantially equal to the penetration depth D.
3, The method as claimed in claim 2, wherein two of said filters are disposed back-to-back and conjoined to form a single element, the actuation wavelengths being directed to be incident on each of the exposed faces of the element.
4. A photochromic filter assembly comprising a plurality of photochromic filters and means for directing actuation wavelengths from incident illumination to be incident on a face of each filter sufficient to activate each filter to the saturation level.
5. An assembly as claimed in claim 4, wherein said directing means comprises an ultra-violet beamsplitter.
6. An assembly as claimed in claim 4 or claim 5, wherein each filter has a thickness substantially equal to the penetration depth D.
7. An assembly as claimed in claim 6, wherein two of said filters are disposed back-to-back and conjoined to form a single element, the directing means being arranged to direct the actuation wavelengths onto each of the exposed faces of the element.
8. An assembly as claimed in any one of claims 4-6 when incorporated in a pair of goggles for human wear to protect the eyes of the wearer from nuclear flash exposure.
9. A method of protecting from high illumination levels an optical device having a predetermined aperture, comprising expanding the incident beam,intercepting the expanded beam with a photochromic filter, and thereafter diminishing the beam size for reception by the aperture of the device, the filter having an area which is sufficiently large to provide protection by functioning at or below its saturation level and being activated by wavelengths contained in the expanded beam.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB9509104A GB2287099B (en) | 1992-03-27 | 1993-03-24 | Photochromic filter assemblies |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB9206686A GB9206686D0 (en) | 1992-03-27 | 1992-03-27 | Photochromic filter assemblies |
Publications (3)
Publication Number | Publication Date |
---|---|
GB9306104D0 GB9306104D0 (en) | 1993-05-12 |
GB2265471A true GB2265471A (en) | 1993-09-29 |
GB2265471B GB2265471B (en) | 1995-11-15 |
Family
ID=10712951
Family Applications (2)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
GB9206686A Pending GB9206686D0 (en) | 1992-03-27 | 1992-03-27 | Photochromic filter assemblies |
GB9306104A Expired - Fee Related GB2265471B (en) | 1992-03-27 | 1993-03-24 | Photochromic filter assemblies |
Family Applications Before (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
GB9206686A Pending GB9206686D0 (en) | 1992-03-27 | 1992-03-27 | Photochromic filter assemblies |
Country Status (1)
Country | Link |
---|---|
GB (2) | GB9206686D0 (en) |
Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB1008538A (en) * | 1960-10-20 | 1965-10-27 | Alvin Melville Marks | Phototropic cells |
US3507552A (en) * | 1965-12-01 | 1970-04-21 | Us Navy | Flashblindness protective apparatus |
US3547545A (en) * | 1965-05-11 | 1970-12-15 | Saint Gobain | Antiglare system and method |
-
1992
- 1992-03-27 GB GB9206686A patent/GB9206686D0/en active Pending
-
1993
- 1993-03-24 GB GB9306104A patent/GB2265471B/en not_active Expired - Fee Related
Patent Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB1008538A (en) * | 1960-10-20 | 1965-10-27 | Alvin Melville Marks | Phototropic cells |
US3547545A (en) * | 1965-05-11 | 1970-12-15 | Saint Gobain | Antiglare system and method |
US3507552A (en) * | 1965-12-01 | 1970-04-21 | Us Navy | Flashblindness protective apparatus |
Also Published As
Publication number | Publication date |
---|---|
GB9306104D0 (en) | 1993-05-12 |
GB2265471B (en) | 1995-11-15 |
GB9206686D0 (en) | 1992-05-13 |
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Legal Events
Date | Code | Title | Description |
---|---|---|---|
PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 20010324 |