WO2015054724A9 - Anti-glare mirrors - Google Patents

Abstract

A spectrally selective mirror having a reflectance percentage between 30.2% and 5.2% for all discrete wavelengths of visible light across a range from 445nm to 635nm, with a first local reflectance maximum between 47.8% and 72.8% in a range from 380nm to 445nm, and a second local reflectance maximum between 54.7% and 79.7% in a range from 635nm to 780nm.

Description

ANTI-GLARE MIRROR

TECHNICAL FIELD

[0001] This international patent applicatio claims priority from Australian provisional patent application 2013903966 filed on 15 October 2013, the contents of which are to be taken as incorporated herein by this reference.

[0002] The present invention relates to mirrors intended for use as rear-view mirrors for vehicles, ideally being spectrally selective mirrors that typically utilise multiple thin layers on a substrate to modify the reflection of incident light to reduce the reflected glare experienced, for example, under night-time driving conditions. While the primary use for the mirrors of the present invention is as rear-view mirrors for vehicles, it will be appreciated that the invention is not to be limited to only that use.

BACKGROUND OF THE INVENTION

[0003] A rear-view mirror is a device intended to provide a means of clear indirect vision to the rear of a vehicle within a defined field of view. Driving is primarily an optical task requiring drivers to process visual information continuously and clear vision is required for visibility (for object detection) and for colour reproducibility (for colour recognition). Clear visibility is required for drivers to detect aids and hazards such as lane lines, signs, pedestrians and vehicles, Colour reproducibility is important for drivers to be able to characterise objects such as traffic lights and traffic control signals. To ensure adequate object detection and colour recognition, legislative requirements require a photopic reflection for rear-view mirrors of not less than 40 percent as measured by SAE J 84, which allows the colours of the signals used for road traffic to be recognized.

[0004] Glare, a visual sensation, is often experienced b drivers at night when exposed to reflected unpleasant bright light in a rear-view mirror. Glare can result from too much light or from the range of luminance in a visual environment being too large. Where too much light is experienced, a simple photophohie response occurs, which forces the viewer to reduce the luminance of the whole visual f ield by a method such as looking away. Alternatively, if glare has resulted from the range of luminance in a visual environment being too large, the effect is disabilit glare or discomfort glare. This type of glare is common on roads at night and is the most relevant for discussing reflected headlights in rear-view mirrors,

[0005] Exposure to glare can reduce visibility which presents a safety concern as driving is particularly reliant on visual information. Exposure to reflected rear-vision mirror glare is unique in two important areas, namely that the exposure is often for a relatively long period of time as trailing cars remain in a relatively fixed position, and that exposure to glare is often compounded as headlights are visible i more than one mirror, As a result, steady glare sources can create a local adaption or a blind spot after the light source is removed from the field of vision, which is an obstacle to satisfactory observation in peripheral vision.

[0006] To alleviate the amount of reflected glare seen at a driver's eyes, a few solutions have been developed and implemented by car manufacturers. E!ectroc romic mirrors (EC) are a complex high cost solution typically seen on luxury cars, which switch from a high to low reflectance state electrochemically when a glare source is sensed. Prismatic mirrors use a wedge-shaped piece of glass and changes in geometry to switch from a high to low reflectance state. These mirrors offer a low cost solution, but need to be manually actuated to change states. Blue mirrors have an anti-glare tint aimed to reduce the amount of long wavelength reflected light seen traditionally in halogen headlamps, thus reducing glare. More recently, a new design for a glare-reducing mirror has been presented (US patent 7,887,201 ), which seeks to reduce blue wavelengths seen in high intensity discharge (HID) lamps where the eye is most sensitive. This latter approach minimises the spectral reflectivity of the mirror where scotopic vision is most sensitive to the reduced glare, resulting in a mirror thai is gold coloured in appearance that has low cosmetic appeal.

[0007] Whilst these options are available to reduce reflected glare, new glare management techniques are required based on human eye glare sensitivity models to optimise a mirror for minimum reflected glare whilst maintaining mirror visibility for object and colour detection. Furthermore, glare management techniques need to account for headlamp technology trends moving away from traditional longe wavelength halogen sources to a mix with short wavelength HID and LED sources. To have the potential to make a tangible impact on the road, an new mirror should reduce glare across all light sources and be manufacturab!e using a practical and cost competitive method.

[0008] Before turning to a summary of the present invention, it must be appreciated that the above description of the prior art has been provided merely as background to explain the contex of the invention. It is not to be taken as an admission that any of the material referred to was published or known, or was a part of the common general knowledge in Australia or elsewhere.

SUMMARY OF THE INVENTION

[0009] The present invention provides a spectrally selective mirror having a reflectance percentage between 30.2% and 55.2% for all discrete wavelengths of visible light across a range from 445nm to 635nm, with a first local reflectance maximum between 47.8% and 72.8% in a range from 380nm to 445nm, and a second local reflectance maximum between 54.7% and 79.7% in a range from 835nm to 780nm.

[0010] A spectrally selective mirror is a mirror that uses one or more characteristics of light, such as interference or absorption, in a manner to alter its reflectance across a discrete portion/portions of the visible wavelength spectrum or across th entire visible wavelength spectrum. The purpose of such a reflectance modification Is to achieve a target reflectance spectrum which will deliver desired optical properties. Examples of spectrally selective mirrors include other anti-glare mirrors, such as th blue mirrors mentioned above. Examples of mirrors which are not spectrally selective included standard glass mirrors with a chrome or metallic surface, which are standard on most vehicles in the modem era.

[0011] By way of explanation, the human eye's sensitivity to glar V_dgi{A) can be described as a combined function of signals produced by the eye's rod receptors, as well as from both the magnocellular and opponent chromatic channels, commonly described as short, medium and long wavelength cone functions, where Λ is the wavelength of light. The technology mix of short and longer wavelength headlamp sources can be characterised by a weighted spectral power distribution W(A) for Halogen, HID and LED sources. With this in mind, V_f.¾i(A) x W(A) then describes the relative glare from headlamp sources a driver is likely to experience across the electromagnetic visible spectrum.

[0012] The present inventors have recognised that to reduce a driver's glare response, a reflected mirror spectrum should be minimised where V_i;,_;!i(A} x VV(A) has maximum relative energy, which is between 51Gnm and 620nm. In addition, the reflected mirror spectrum should also be maximised as ν<¾ι(λ) x W(A) tends towards zero at about 400nm and about 7S0.nm respectively.

[0013] Further, the reflected spectrum that is optimised to reduce the driver's glare response ideally will also be optimised for a driver's in-car positio viewing angle, which typically ranges from 30 degrees to 70 degrees depending on vehicle geometry. In this respect, the reflectance spectrum of the mirror of the presen invention will ideally be apparent at a driver's viewing angle between 0 degrees to 90 degrees, preferably between 30 degrees and 70 degrees but most preferably at 45 degrees. The driver's viewing angle is the angle of incidence between the driver's line of sight with the mirror image and the line perpendicular or normal to the mirrors surface

[0014] The reflectance spectrum of a spectrally selective mirror in accordance with the present invention can be described to fall within a region bound by the following equations, where Υ(λ) is a measure of the reflectance at a driver's viewing angle (%) at wavelength λ (nrn):

A, < Υ(λ) - -0.272 A + D < k₂

A₂ < Y(A) ~ C < A₃

where Ai = 380 nm and where C = 42.7 ± 12.5

A₂ ~ 445 nm D =^■ 16.3.7 ± 12.5

A₃ ~ 635 nm E = -62.3 ± 12.5

λ ~ 780 nm

[0015] In an alternative form of the present invention, the region may be narrower such that C = 42.7 ± 10.0, D = 163.7 ± 10.0 and E ~ -62.3 ± 10.0. Further, the region may be narrower stilt such that C = 42.7 ± 5,0, D = 163,7 ± 5.0 and E = -62.3 ± 5 0. Further still, the region may be narrower again such that C ^~ 42.7 ± 2.5, D ~ 163.7 ± 2.5 and E = -82.3 ± 2.5.

[0016] A local reflectance maximum at a discrete wavelength is a maximum value within a specific range. It is defined as that point on a reflectance vs wavelength curve which has a first derivative of zero and a second derivative which remains either positive or negative on wavelengths directly adjacent, above or below this point. Alternatively, a local reflectance maximum can be a point which lies on the bounds of a range such as λι or A₄ where the reflectance value at this point is a maximum within the range and there is no value within the range having a first derivative of zero.

[0017] In a preferred form, the spectrally reflective mirro is provided by a substrate having a coating thereon- I one form, the coating is a multi-layered interference coating, which will be described below.

[0018] The substrate of the preferred form may be formed from a suitable polymeric or plastic material, or from a metal, a glass, or any other suitable material or blends thereof.

[0019] For example, a plastic substrate may be formed from a material selected from the group including polyacrylate, polyester, polystyrene, polyethylene, polypropylene, polyamides, polyamides, polycarbonate, epoxy, phenolic, acrylonltrile- butadiene-styrene, acryloniirile-styrene-acrylates, acetal and blends of these. Preferred plastic substrate materials include polycarbonate, poly {2:2'- dihydroxyphenylpropane) carbonate, polydiethyleneglycol bis(aJlyl carbonate), polymethylmethacrylate and polystyrene, or blends thereof.

[0020] A glass substrate may be formed from a material selected from the group including silica, soda lime glass, horosiiicate glass, fused silica glass, lead-oxide glass, oxide glass, aluminosllicate glass, or blends thereof.

[0021] A metal substrate may be formed from a material selected from the group including aluminium, boron, chromium, cobalt, copper, iron, magnesium, molybdenum, nickel, niobium, stainless steel, tantalum, tin titanium, tungsten, vanadium, zinc, zirconium and mixtures thereof; and an oxide, nitride, beside or carbide thereof, and mixtures thereof.

[0022] In preferred forms, the substrate will typically have a physical thickness in the range of 0.1mm to 20mm, more preferably in the range of 1mm to 5mm, and most preferabl in the range of 2mm to 3mm.

[0023] The multi-layered interference coating of the preferred form may include up to 30 alternating layers of materials of different refractive indices, ideally with a relatively high refractive index contrast between adjacent layers, in this respect, such a refractive index contrast ca be achieved by the selection of a material with a suitably low refractive index and another material with a suitably high refractive index. Th refractive index can be considered as a complex number which is made up of the real part (defined as refractive index) and the imaginary part (defined as the absorption coefficient). The amount of light that is reflected can then be determined by the optical thickness, where optical thickness is a dimensionless measure of how much a given material retards the passage of light therethrough, derived from the multiplicatio of the complex refractive index and the distance travelled through the material by a light beam.

[0024] With this in mind, high refractive index materials may be selected from the grou including: chromium, aluminium, titanium, nickel, molybdenum, zirconium, tungsten, silicon, niobium, tantalum, vanadium, cobalt, manganese, silver, zinc, and mixtures thereof; and an oxide, nitride, boride, fluoride or carbide thereof, and mixtures thereof. Most preferably, at least one layer is chromium, or a chromium mixture, such as Cr-Zr, Cr-Ni or Cr- o, or carbides or nitrides thereof, such as Cr-N.

[0025] Low refractive index materials may be selected from the group including: boron, silicon, germanium, antimony, tellurium, polonium, niobium, zirconium, magnesium, tin, tantalum, aluminium, chromium, titanium and mixtures thereof; and an oxide, nitride, boride, fluoride or carbide thereof, and mixtures thereof. Most preferably, at least one layer is formed from an oxide such as 8ί(¾,

[0026] Before exemplifying the interaction of a material's refractive index, optical thickness and physical thickness, it should be generally appreciated that for any given layer of a material the optical thickness (t) is defined as the material's refractive index (n) multiplied by the layer's physical thickness (d), normalised at the handled wavelength, for a refractive index at this, wavelength. In one embodiment, optical thickness is calculated using a refractive index at a wavelength of 550nm. For example, chrome:

having a physical thickness of 50nm corresponds to an optical thickness of 0.288, whil Si0₂ ^nsso^l ^SS, having a physical thickness of lOOnm corresponds to an optical thickness of 0.285,

[0027] In a preferred form, the multi-layered interference coating includes at least three layers and has opposed outermost layers, either one or two innermost layers (one where the number of layers in the coating is odd and two where the number of layers in the coating is even), and an even number of intermediate layers between an outermost layer and the innermost layers (there being zero intermediate layers when the total number of layers is three or four). In this form, the optical thickness of the outermost layers is less than the optical thickness of the innermost layers, and the optical thickness of each layer increases from one layer to the next layer, in a manner such that the innermost layers have the largest optical thickness.

[0028] In a preferred form, each layer of a multi-layered interference coating will preferably have an optical thickness in the range of about 0.013 to about 1.058, more preferably in the range of from about 0.026 to about 0.899, and most preferably will be a thickness of about 0.034 to 0.767.

[0029] By way of illustration, where the multi-layered interference coating includes five alternating layers of materials of different refractive indices, with a relatively high refractive index contrast between adjacent layers, the following would be ideal (with layer 1 being closest to the substrate). a. For layer 1 , a material will be selected from the group including a metal, a metalloid, an oxide, fluoride or nitride of a metal, an oxide, fluoride or nitride of a metalloid, or carbon (such as a diamond-like carbon (DLC)), and will preferably have an optical thickness in the range of from about 0,013 to about 0.794, more preferably i the range of from about 0.026 to about 0.132, and most preferably will be a thickness of about 0.050 to 0.058. Preferably, the material will be SiG>2. b. For layer 2, a material will be selected from the grou including chromium, aluminium, titanium, nickel, molybdenum, zirconium, tungsten, silicon, niobium, tantalum, vanadium, cobalt, manganese, silver, zinc, and mixtures thereof, and an oxide, nitride, boride or carbide thereof, and mixtures thereof, and will preferably have an optical thickness in the range of from about 0.029 to about 0.481 , more preferably in the range of from about 0.173 to about 0.288. and most preferably will be a thickness of about 0.213 to 0.248. Preferably, the material will be Cr. c. For layer 3, a material will be selected from the group including a metal, a metalloid, an oxide, fluoride or nitride of a metal, an oxide, fluoride or nitride of a metalloid, or carbon (such as a diamond-like carbon (DLC)), and will preferably have an optical thickness in the range of from about 0.285 to about 1.058, more preferabiy in the range of from about 0.881 to about 0.899, and most preferably will be a thickness of about 0,714 to 0.767. Preferabiy, the material will be SiC½. d. For layer 4, a material will be selected from the group including chromium, aluminium, titanium, nickel, molybdenum, zirconium, tungsten, silicon, niobium, tantalum, vanadium, cobalt, manganese, silver, zinc, and mixtures thereof, and an oxide, nitride, boride or carbide thereof, and mixtures thereof, and will preferably have an optical thickness in the range of from about 0.029 to about 0.461 , more preferably in the range of from about 0.058 to about 0.173 , and most preferably will be a thickness of about 0.121 to 0.144. Preferably, the material will be Cr. e. For layer 5, a material will be selected from the group including a metal, a metalloid, an oxide, fluoride or nitride of a metal, an oxide, fluoride or nitride of a metalloid, or carbon (such as a diamond-like carbon (DLC)}, and will preferabl have an optical thickness in the range of from about 0.013 to about 0.794, more preferabiy in the range of from about 0.026 to about 0.132, and most preferably will be a thickness of about 0.029 to 0.042. Preferably, the material will be Si0₂.

[0030] Where the substrate is opaque, the multi-layered interference coating can be applied to a first surface to form the mirror, where the first surface is defined as the surface in-between the substrate and a person viewing the mirror image. Where the substrate is transparent, the multi-layered interference coating can be applied to the first surface or a second surface, or a combination of the first and second surfaces, where the second surface describes the situation where th multi-layered coating is viewed through a substrate which is positioned between the multi-layered coating and the person viewing the mirror image.

[0031] Preferred deposition methods that may he adopted for applying the multilayered interference coating to a substrate, or to a hardcoated substrate as will foe described below, can be chosen from any vacuum vapour deposition system, such as thermal evaporation, electron beam evaporation (with or without ion beam assistance) or sputter deposition. Sputter deposition is the preferred method. Additionally the surface of the substrate, or of the hardcoated substrate, may first be subjected to a surface treatment to improve adhesion between the multi-layered interference coating and the substrate (or the hardcoated substrate). Th surface treatment may be selected from any of plasma discharge, corona discharge, glow discharge and UV radiation.

[0032] The mirror of the present invention may also include other coatings either between the multi-layered interference coating and the substrate, within the multi- layered interference coating, or upon the multi-layered interference coating, such as a hard coating. A coating that is said to be a "hard coating" is a coating that is harder and stiffer than the substrate whereby it increases the abrasion resistance of that substrate. An abrasion resistant coating is one that reduces damage due to impacts and scratching. Abrasio resistance can be measured through tests such as ASTM F735 "Standard Test Method for Abrasion Resistance of Transparent Plastics and Coatings Using the Oscillating Sand Method", ASTM D4060 "Standard Test Method for Abrasion Resistance of Organic Coatings", by the Taber Abrader, or by using the well-known Steelwool Test.

[0033] Furthermore, some plastic substrates can be damaged by certain solvents; for example, polycarbonate is damaged b acetone. It is a requirement in the automotive industry for a mirror to be "chemically resistant", which is a reference to an ability to withstand exposure to normal solvents such as diesel fuel, petroleum, battery acid, brake fluid, antifreeze, acetone, alcohol, automatic transmission fluid, hydraulic oil and ammonia based window cleaners. In this respect, it will be appreciated that a hard coating ideally provides the mirror of the present invention with such chemical resistance. [0034] A hard coating for the mirror of the present invention is preferably formed from one or more abrasion resistant layers, and may include a primer layer that bonds well to a plastic substrate (where the substrate is plastic) and forms a preferable material for subsequent abrasion resistant layers. The primer layer may be provided by any suitable material and may for example be an organic resin such as an acrylic polymer, a copolymer of acrylic monomer and methacryioxysliane, or a copolymer of a methacrylic monomer and an acrylic monomer having a benzotriazole grou or benzophenone group. These organic resins may be used alone or in combinations of two or more.

[0035] The abrasio resistant layers are preferabl formed from one or more materials selected from the group consisting of an organo-silicon, an acrylic, a urethane, a me!amine or an amorphous SiO_xC_yH_E. Most preferably, the abrasio resistant layer is an organo-silicon layer, due to its superior abrasion resistance and compatibility with physical vapour deposited films. For example, an abrasion resistant layer comprising an organo-silicon polymer can be formed by forming a layer of a compound selected from the following compounds by a method such as dip coating or the like and then curing the layer: t ialkoxysilanes or triacyloxysi lanes such as meth yltri methoxysi la ne , methyltriethoxysilane, methyltrimethoxyethoxysilane, neihylinaceioxysi!ane, methyltripropoxysilane, methyi ributoxysiiane,

ethy!tnmethoxys!!ane, ethyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltracetoxysilane, vinyltrimethoxyethoxysila e, phenyitrimethoxysila e,

phenyltriethoxysiiane, phenyltriacetoxysilane, gamma-chloropropyltnmethoxysilane, gamma-chloropropyltrieihoxysilane, gamma-chloropropyitripropoxysilane, 3,3,3- trifluoropropy!frimethoxysilan gamma-glycidoxypropyltrimethoxysilane, gamma- glycidoxypropyltnethoxysilane, gamma-(beta-glycidoxyethoxy)propyltrimethoxysilane, beta~(3,4~epoxycyclohexyl)ethyitriniethoxysilane, beta-(3,4- epoxycyclohexyl}ethyltriethoxysilane, gamma-methacryloxypropyltrimethyoxysilane, gamma-aminopropyltrimethoxysilane, gamma-ammopropyltriethoxysilane, gamma- meraptopropyltrimethoxysiiane, gamma-mercaptopropyltriethoxysilane, N- beta(am!noethyi)~gamma-aminopropyltrimethOxys!lane, beta- cyanoethyltriethoxysilane and the like; as well as dialkoxysilanes or diacyloxysilanes such as dimethyldimethoxysilane, phenylmethyldimethoxysilane,

dsmethyldiethoxysilane, phenylmethyldsethoxysilane, gamma- glycidoxypropyimethyldimeihoxysilane, gamma-glycidoxypropylmethyidtethDxys lane, gamma-glycdoxypropylphenyldimethOxysilane, gamma- glycidoxypropylphenyidiethoxysilane, gamma-chloropropyimeihyldlmeihoxysilane, gamma-chtoropropylmeihy!dsethoxysi!ane, dimethyldiacetoxysilane, gamma- methacryloxypropylmethyldimethoxysilane, gamma- metacryloxypropylmethyldiethQxysilane, gamma- mercapiopropy!methyldlmethoxysi!ane., gamma-mercaptopropyimethyldiethoxysiiane, gamma-aminopropylmeihy!dsmethoxysilane, gamma- aminopropylme hyldie hoxysilane, methylvinyldimethoxysi!ane,

methylvinyidiethoxysilane and the like.

[0036] The abrasion resistant layers ma be coated onto a plastic substrate b dip coating in. liquid followed by solvent evaporation, or by plasma enhanced chemical vapour deposition (PECVD) via a suitable monomer. Alternative deposition techniques such as flow coating and spray coating are also suitable. To improve the abrasion resistance of the hard coating, subsequent coatings of the abrasion resistant layer may be added, preferably within a 48 hour period to as to avoid aging and contamination of the earlier coatings.

[0037] The thickness of an abrasion resistant layer is preferably selected to assist in providing adequate abrasion resistance. In this respect, adequate abrasion resistance is regarded herein as being a Bayer abrasion ratio of 5 with respect to an uncoated plastic substrate (such as a polycarbonate), or alternatively by a Taber abrasion test with delta haze less than 6% after testing with a 500g load and CS10F wheel at 500 cycles, {% haze being measured as per ASTM D1003). With these requirements met, when an organo-silicon is used as an abrasion resistant layer, the thickness of the hardcoating is preferably in the rang of from about 3 to about 15 microns, and is most preferably between 3 and 7 microns.

[0038] In a preferred form of the mirror of the present invention, a cap layer ma also be provided on the multi-layer interference coating to further enhance the abrasion resistance and cleanability. For example, a cap layer may b formed from a material exhibiting the following characteristics, including hydrophobic, hydrophiiic, lipophobic, lipophilic and oleophobic characteristics or combinations thereof. [0039] The mirror of the present invention has been found to allow for the minimising of the mirrors reflectance spectrum where the "human eye discomfort glare spectral sensitivity function multiplied by weighted spectral power distribution of headlamps on the road" is at a maximum. It has also been found to allow for the mirror's reflectance spectrum to be maximised where the "human eyes discomfort glare spectral sensitivity function multiplied by weighted spectral power distribution of headlamps o the road" tends towards zero. Furthermore, it has been found that disabilit and discomfort glare are both positively correlated with illuminance on the eye and hence mirror reflectance.

[0040] Additionally, it has been found that th mirror of the present invention minimises the normal coefficient of reflection and provides an acceptable Colour Rendering Index (CRI) by comparison to alternative mirrors on the market. CRI is calculated as defined in CIE 2005 using a method to determine how closely an optical element, such as light or mirror reflection, can reproduce colours benchmarked against a natural light source on a scale of 1-100, where 100 represents perfect colour reproduction. The present invention provides a passive mirror with glare reduction and object detection properties functional 100% of the time, while mirror object detection is comparable to other mirrors rated as fair with respect to reducing glare.

Brie Description of Drawings

[0041] The present invention will now be described in relatio to various preferred embodiments of which some aspects are illustrated in the accompanying figures, with other aspects being illustrated by the following examples. In the figures:

[0042] Figure 1 is a schematic cross section of one embodiment of a mirror that is in accordance with the present invention;

[0043] Figure 2 is a table providing a weighted technology summary from 2012 of vehicle headlight technology in the automotive market

[0044] Figure 3 is a comparison of typical spectral power distribution for halogen (CIE illuminant A), HID (Phillips D2S) and LED headlamps (YAG Ohno. 2004); [0045] Figure 4 shows a function of Relative Energy vs Wavelength vs Reflectance Spectrum, showing a weighted headlight spectrum, a weighted headlight spectrum x discomfort glare sensitivity function, a discomfort glare sensitivity function, and a spectrum for a mirror in accordance with an embodiment of the present invention;

[0048] Figure 5 is a schematic view of the SPEOS simulation geometric test setup;

[0047] Figure 6 is a schematic view of the target geometry of a test set-up; and

[0048] Figures 7(a) to 7(f) are the reflectance spectrums of each of Examples 1 to 6 respectively, as referred to in each of Tables 2, 4, 6, 8, 10 and 12 respectively, showing the exemplary reflectance spectrum relative to the upper and lower boundaries set by the present invention.

Detailed Description

[0049] Figure 1 is a schematic cross section of two embodiments of a mirror in accordance with the present invention. In a first embodiment, the substrate is a polycarbonate substrate, onto which is coated a hardcoat in the form of a single abrasion resistant layer about 3 microns in thickness. A multi-layered interference coating in the form of five alternating layers of materials of different refractive indices is coated onto the hardcoat in a total thickness of about 378nm. Coated onto the interference coating is a hydrophobic cap layer of about 15n.m. In a second embodiment, the substrate is a soda lime glass substrate, onto which a multi-layered interference coating in the form of five alternating layers of materials of different refractive indices is coated onto the soda lime glass in a total thickness of about 378nm. Coated onto the interference coating is a hydrophobic cap layer of about 15nm. It is mirrors of these general types that are the subject of the Examples provided below.

[0050] To establish a weighted spectral power distribution of headlamps on the road, the 2011 weighted technology mix values as shown in Figure 2 were multiplied by the halogen, HID and LED power distribution spectrums shown in Figure 3 respectively, across the visible region between 380nm to 780nm. The proposed discomfort glare sensitivity model of Fekete et at (2010) (see below) was then calculated across 380nm to 780nm and multiplied by the weighted spectral power distributio of headlamps. This yielded a spectrum with maximum relative energy values above 0.7 lying between 51Gnm to 820nm as seen in Figure 4. The spectrum approaches zero reflectivity at 400 m and 75Gnm.

[0051 ] Following this, thin film coating software was utilised to optimis the mirrors reflective spectrum minimising the spectrum between 510nm to 620nm and maximising the spectrum as zero reflectivity is approached at 400nm and 750nm. The optimisation was performed using coating layers of chrome and silica at an arbitrary mirror viewing angle of 45 degrees. An optimised mirror of the same general type as illustrated in Figure 1 , with, a nominal reflectance of 45% across the visible spectrum, was achieved as shown in Figure 4.

[0052] The following examples illustrate some preferred embodiments of mirrors in accordance with the present invention. However, it should be understood that the following examples are illustrative only and should not be taken as a restriction on the generality of the invention as described above. An analysis of these preferred embodiments of the present invention follows the examples.

Example 1

[0053] A transparent soda lime glass substrate was first cleaned through a commercial ultrasonic cleaning system with detergent. A final rinse in distilled water was required in a clean (dust free) environment. The substrate was Ioaded into a batch type electron beam physical vapour deposition vacuum chamber equipped with an ion gun. The following were the deposition conditions where the thickness values are defined as an input value on the crystal rate monitor of the vacuum deposition chamber which have been calibrated to provide a corrected thickness. Pre Layer 1 Layer 2 Layer 3 Layer 4 Layer 5 Cap Laye treatment

Ion 1 minute on on on on on Off assistance

beam

Crucible Sfiicon Chromium Sfiicon Chromium Silicon Hydrophobic material 99:95% 99.96% 99.95%: 99.95% 99.95%: material

Base 2e-5m ar 2e-5 2e-5 2e~S 2e-5 2e~S 2e-5

Pressure

(mbar)

Run 2e-4 2e-4 2e-4 2e-4 2e-4 2e-4 3e~4

Pressure

(mbar)

Deposition 10 2.5 10 2.5 10 10

Rate CA/s)

Thickness 20nm 40nm 280nm 23nm 11nm 15nm

Table 1 ^■■■ Example 1

[0054] SPEOS V2G, a light modelling software package was used to evaluate spectrum glare reduction. A 3D mode! of a driver and mirror of approximately 0.02m² reflective surface area in a standard in-car position was set up. A headlamp light source was added to the model at a distance of 10.7 m behind the drivers mirror in a position that simulated a vehicle in a neighbouring lane that might actually be found on a two lane road, as demonstrated in Figure 5. Th reflected light from the mirro hit the driver^'s eye at an angle of 45 degrees. The model was run for various combinations of headlamps and reflective spectrums to provide data for glare calculations using a 10 million light ray trace. Simulation results showed a glare reduction using the novel said spectrum compared to a standard chrome mirror, a blue antiglare mirror and a gold antiglare mirror, across all light sources. The upper and tower tolerance limits placed on the spectrum of the invention were also evaluated to ensure enhanced glare performance at these limits.

[0055] The upper spectrum limit was defined by:

Ai < Y(A) = -0.272 A + 176.2 < ,½

λ₂ < Υ(λ) = 55.2 < λ₃

A₃ Υ(λ) - 0.188 A -49.8 λ₄

where A< = 380 nm, A₂ = 445 nm, A₃ = 635 nm_; A₄ ~ 780 nm [0056] The lower spectrum limit was defined by

Ai < Υ(λ) = -0.272 A + 151.2 < A₂

λ₂ < Υ(λ) = 30.2 λ₃

λ₃≤Υ(λ) - 0.168 λ -74.8≤λ₄

where Α-: - 380 nm, λ₂ = 445 nm, λ₃ = 635 nm, λ₄ = 780 nm

[0057] Simulation results showed a glare reduction using the inventive spectrum's upper limit spectrum and lower limit spectrum when compared to a standard chrome mirror. For the upper spectrum tolerance across all light sources, the De Boer rating averaged approximately 1.35 and improved disability glare on a standard chrome mirror by approximately 12%. For the lower spectrum tolerance across all light sources, the De Boer rating averaged approximately 1.81 and improved disability glare on a standard chrome mirror by approximately 48%. For the inventive spectrum across all light sources, the De Boer rating averaged approximately 1 .56 and improved disability glare on a standard chrome mirror by approximately 30.5%.

[0058] The De Boer scale (1967) is the most widely used assessment of discomfort glare, and provides a rat ng of a glare sources induced discomfort on a scale of one to nine. Schmidt-Clausen and B!ndels ( 974) approximation was used to estimate these De Boer ratings. Disability Glare, the reduction in visual performance due to light scatter in the eye which reduces the luminance contrast of the retinal image, is estimated by the veiling luminance using a CIE standard observer.

[0059] Eye illuminance values from SPEOS V20 optical output were used to calculate discomfort glare and disability glare. The following value for La was used: 1 .2 cd/m² on commercial roads at night-time. Median driving age of an observer was taken as 40 years old.

[0060] The simulated setup was approximately transposed to actual lab conditions to validate the simulation glare improvements. Three headlamps were generally compared in various of these investigation as examples of the three existing technologies; a haloge Ford Falcon, a HID Toyota Ultima and an LED Toyota Prius.

[0061] Headlamps were energised to 13.5 V (Halogen & HID) and 29 V (LED) in a darkroom with light aimed towards the mirro in a geometric setup wher the headlamps position was 10 m behind the mirror and 9.375 m behind a lux meter with a lateral offset of 685 mm. This position simulated a headlamp position of following traffic that may be found on a road. The lux meter position simulated a human's eye in car position with mirror reflection at an angle of 45 degrees in three dimensions. Reflected illuminance from the mirror was measured according to the experimental setup layout in Figure 8. Calculations for De Boer ratings and Disability Glare improvement on a standard chrome mirror were applied using a similar methodology as the SPECS simulation.

[0062] The average Disability Glare improvement on standard glass mirro coated with chrome will ideall be greater than 10% for the mirrors of the present invention, when calculated and averaged across Halogen, HID and LED headlam sources. This characteristic is evaluated using the mirrors reflectance spectrum as an input into a simulation using SPEOS V20 light modelling software package or equivalent. A 3D model in such a simulation consisted of a driver and a mirror of approximately 0.02m² reflective surface area in a standard in~car position. A headlamp light source was modelled at a distance of 107 m behind the driver's mirror with a lateral offset away from the vehicle of 1.8m, depressed 0.61 m below the mirror's height. This simulated a vehicle in a neighbouring lane. The simulation was run with a lOmillion light ray trace. Evaluation of disability glare is ideally at an age of 40 years.

[0083] Adrian' Visibility model 1989, which specifies a visibility level model, was used to assess mirror object detection properties. A modified small target visibility model with an object 180 x 180cm and 50% reflectance placed 2 meters behind the rear vision mirror surface, scored a visibility level of approximately 4.2 under sodium and metal halide ambient lighting conditions.

[0084] Table 2 below provides results of the testwork on the mirror of Example 1. 1< 3

Photopic reflectance @ 45^'° j Y= 40.5 %

Colour target on transparent glass L* = 69,5

substrate - CIE L*a*b^* scale measured a* = -2.96

with illuminant A/2 @ 0^s b^*—10.15

CRI (colour rendering index) @ 45^: 92

Average De Boe Rating @ 45 1.5

Average Disability Glare improvement 29%

on standard chrome mirror @ 45

Visibility level @ 45^° 4.0

Reflectance Spectrum @ 45 degrees: see Figure 7(a)

Table 2 : Physical Characteristics i¾ 45 deqree driver's viewinq anqle

Exam le 2

[0065] A transparent soda lime glass substrate was first cleaned through a commercial ultrasonic cleaning system with detergent. A final rinse in distilled water was required in a clean (dust free) environment. The substrate was ioaded into a batch type electron beam physical vapour deposition vacuum chamber equipped with an ion gun. The following were the deposition conditions where the thickness values are defined as an input values on the crystal rate monitor of the vacuum deposition chamber which have been calibrated to provide a corrected thickness.

Pre Layer 1 Layer 2 Layer 3 Layer 4 Layer 5

treatment

Ion 1 minute on on on on on

assistance

beam

Crucible Silicon Chromium Silicon Chromium Siiieon materia! 99.95% 99.95% 98.95% 99.95% 98.95%

Base 2e-5mfear 2e-5 2e-5 2e-S 2e-5 2s-5

Pressure

fro bar)

I Run 2e- 2e-4 2e-4 2e-4 2e-4 2e-4

Pressure

(mbar)

Deposition 10 2.5 10: 2.5 10

Rate (A/s)

j Thickness 20nm 40nm 280nm 23nm 11 nm

Table 3^■■■ Example 2

[0088] Table 4 provides the results of the testwork on the mirror of Example 2.

Photopic reflectance @ 45° Y= 44.5 %

Colour target on transparent glass L* = 71.5

substrate - CIE L*a^*b^* scale measured a* = -3.8

with iiluminant A2 @ 0^° b* - -9.6

CRI (colour rendering index) (§> 45" 92

Average De Boer Rating @ 45^° 1.5

Average Disability Glare improvement 29%

on standard chrome mirror @ 45"

Visibility level @ 45^" [ 4.4

Reflectance Spectrum @ 45 degrees: see Figure 7(b)

Table 4 : Physical Characteristics @ 45 degree driver's viewing angle Example 3

[0067] A transparent soda lim glass substrate was first cleaned through a commercial ultrasonic cleaning system with detergent. A final rinse in distilled water was required in a clean (dust free) environment. The substrate was loaded into a batch type electron beam physical vapour deposition vacuum chamber equipped with an Ion gun. The following were the deposition conditions where the thickness values are defined as an input values on the crystal rate monitor of the vacuum deposition chamber which have been calibrated io provide a corrected thickness.

Table 5 - Example 3

[0088] Table 6 provides the results of the testwork on the mirror of Example 3.

Photopic reflectance @ 60" Y= 40%

Colour target on transparent glass L* = 73.08

substrate - CIE L^*a^*b^* scale measured a* ~ -2.45

with illurninant A/2 @ 0^s b* ~ -6.27

CR! (colour rendering index) @ 80 92

Average De Boer Rating @ 60 1.5

Average Disability Glare improvement 29%

on standard chrome mirror @ 80^°

Visibility level @ 60 4,0

Reflectance Spectrum @ 60^": see Figure 7(c) Example 4

[0069] A transparent soda lime glass substrat was first cleaned through a commercial ultrasonic cleaning system with detergent. A final rinse in distilled water was required in a clea (dust free) environment. Th substrate was loaded into a batch type electron beam physical vapour deposition vacuum chamber equipped with an ion gun. The following were the deposition conditions where the thickness values are defined as an input values on the crystal rate monitor of the vacuum deposition chamber which have been calibrated to provide a corrected thickness.

[0070] Table 8 provides the results of the testwork on the mirror of Example 4.

Photopic reflectance @ 30^° Y= 47.5%

Colour target on transparent glass L* ~ 63.66

substrate - CIE L*a*b^* scale measured a* ~ 0.46

with illuminant A/2 @ 0^° b^* - -4.25

CRI (colour rendering index) @ 30^° 92

Average De Boer Rating @ 30^° 1.5

Average Disability Glare improvement 29%

on standard chrome mirror @ 30^"

Visibility level @ 30 4.2

Reflectance Spectrum @ 30^'': see Figure 7(d)

Table 8 : Physical Characteristics (a⁾ 30 degree driver's viewing angle Example 5

[0071] An injection moulded polycarbonat substrate was first cleaned through a commercial ultrasonic cleaning system with detergent. A final rinse in distilled water was required in a clean (dust free) environment. The substrate was then dip coated i a SDC TSR 2828B at a withdrawal rate of 10mm/s. A flash-off time of 10 minutes allowed solvents to slowly evaporate and the part to be largely tack free. The substrate was then moved to a curing oven for 90 minutes at 130°C. Subsequent coatings were performed within a 48 hour period so as to avoid aging/ contaminating of the hardcoat.

[0072] Samples were transferred to a holding oven maintained at 60 ^aC, which ensured the plastic remained dry and helped reduc pump down times when transferred to the vacuum chamber.

[0073] The substrate was loaded into a batch type electron beam physical vapour deposition vacuum chamber equipped with an ion gun. The following were the deposition conditions where the thickness values are defined as an input values on the crystal rate monitor of the vacuum deposition chamber which have been calibrated to provide a corrected thickness.

Table 9- Example 5 [0074] Table 10 provides the results of the testwork on the mirror of Example 5.

Photop c reflectance @ 45° Y= 43.1 %

Colour target on transparent glass L* ~ 71.4

substrate - CIE L*a^*b^* scale measured a^* ~ -2.8

with illuminanf A/2 @ 0^° h^* - -9.7

CRI (colour rendering index) (§> 45" 92

Average De Boer Rating @ 45^° 1.5

Average Disability Glare improvement 29%

on standard chrome mirror @ 45"

Visibility level @ 45^" 4.2

Reflectance Spectrum @ 45^'': see Figure 7(e)

Table 10 : Physical Characteristics (a) 45 degree drivers viewing angle

Example 8

[0075] A soda lime glass substrate with an existing first surface chrome layer was first cleaned through a commercial ultrasonic cleaning system with detergent. A final rinse in distilled water was required in a clean (dust free) environment. The substrate was Ioaded into a batch type electron beam physical vapour deposition vacuum chamber equipped with an ion gun. The following were the deposition conditions where the thickness values are defined as an input values on the crystal rate monitor of the vacuum deposition chamber which have been calibrated to provide a corrected thickness. Deposition occurred on the first surface chrome layer.

Pre Layer 1 Layer 2 Layer 3 Layer 4 Layer 5 Cap Layer treatment

Ion 1 minute on on on on on Off assistance

beam

Crucible Sfiicon Chromium Sfiicon Chromium Silicon Hydrophobic material 99:95% 99.96% 99.95%: 99.95% 99.95%: material

Base 2e-5m ar 2e-5 2e-5 2e~S 2e-5 2e~S 2e-5

Pressure

(mbar)

Run 2e-4 2e-4 2e-4 2e-4 2e-4 2e-4 3e~4

Pressure

(m ar)

Deposition 10 2.5 10 2.5 10 10

Rate CA/s)

Thickness 20nm 40nm 280nm 23nm 11nm 15nm

Table 11 ^■■■ Example 6

[0076] Table 12 provides the results of the testwork on the mirror of Example 6.

[0077] Three performance aspects of the mirrors of these examples were evaluated, object detection, colour recognition and reflected glare. Results using a modified small target visibility model demonstrated that visibility levels of the mirror are of a suitable level for object detection. Visibility levels above four were calculated under various night street lighting conditions on a commercial road, which are comparable with th "Flabeg Gold" mirror. Acceptable visibility is an expected result as legislative reflectance requirements have been met which are in place to address visibility concerns (UNECE, 2012).

[0078] A blue antiglare mirror reported a visibility level of above five whilst a standard chrome mirror reported a visibility level above seven. An EC mirror in its darkened state recorded a visibility level below one, which is noted as the limit of detectability under laboratory conditions.

[0079] CRI for the mirrors of the present invention is ideally above 80. I relation to the mirrors of the examples, the CRI proved to be of an acceptable level of 92. This is significantly higher than other glare reducing mirror types which rated between 69 and 85, although a standard chrome mirror produced a CRI of 96 which was slightly higher than the mirror of the examples.

[0080] Across all glare simulations and metrics the mirror of the examples resulted in a larger reduction of reflected glare when compared to a standard mirror, the blue antiglare mirror, a bleached EC mirror and the "Flabeg Gold" mirror. However, the EC mirror in its darkened state provided a significant further glare reduction. The SPEOS light study simulation demonstrated under certain conditions the mirror of the examples reduced disability glare 30% more in magnitude over a standard mirror across all headlamp sources. The blue, gold and bleached EC mirror showed a disability glare reduction between 7 and 19% over a standard mirror across all headlamp sources. EC in its darkened state showed a significantly better result ove 82% glare reduction ove a standard mirror across all headlamp sources. Discomfort glare data conferred with disability glare results.

[0081] Laboratory results on th mirrors of the examples showed a similar pattern, where the mirrors of the examples had a higher reduction in disability and discomfort glare across all headlamp sources. The experimental results showed a disability glare reduction of 28% in magnitude over a standard mirror across all headlamp sources. Th blue and gold mirror showed a disability glare reduction between 7 and 25% over a standard mirror across all headlamp sources. EC showed a better result over 91 % glare reduction over a standard mirror across all headlamp sources. Discomfort glare data again conferred with disability glare results. [0082] Discomfort glare De Boer ratings for the mirrors of the examples were consistently above Blue and Gold antiglare mirrors, however were significantly less than EC mirrors.

[0083] The mirrors of the present invention relate generally to headlamp glare sources and the spectral compositions drivers are likely to be exposed to by reflection in rear view mirrors, The spectral composition's effect on the human eye highlights a human eye glare sensitivity function for discomfort glare, which the inventors were able to consider in the design of a mirror aimed at glare control through reflective spectrum alteration. The experimental work demonstrated a driver would be exposed to a reduction in discomfort and disabilit glare when compared to a standard mirror and existing antiglare mirror designs, whilst maintaining a suitable visual performance and colour recognition. Mirrors in accordance with the invention are able to be manufactured with the desired reflective spectrum and controlled laboratory validation on these samples showed a pattern supporting simulated results. The new mirror design provided excellent all round performance for glare reduction with high levels of colour rendition and object detection, all in a passive device.

[0084] A perso skilled in the art will understand that there may be variations and modifications other than those specifically described. It is to be understood that the invention includes all such variations and modifications. The invention also includes all steps, features, compositions and compounds referred to, or indicated in this specification, individually or collectively, and any and all combinations of any two or more of the steps or features.

[0085] References

FEKETE, J., SI -LANYI, C. & SCHANDA, J. 2010. Spectral discomfort glar sensitivity investigations. Ophthalmic and Physiological Optics, 30, 182-187.

Claims

The claims defining the invention are as follows;

1. A spectrally selective mirror having: a. a reflectance percentage between 30.2% and 55.2% for all discrete wavelengths of visible light across a range from 445nm to 835nm; with b. a first local reflectance maximum between 47.8% and 72.8% in a range from 380nm to 445nm, and a second local reflectance maximum between 54.7% and 79,7% in a range from 835nm to 780nm.

2. A spectrally selective mirror according to claim 1 , having a reflectance spectrum within a region bound b the following equations, where Y(A) is a measure of the reflectance at a driver's viewing angle (%) at wavelength A (nm):

λι < Υ(λ) = -0.272 A + D < λ₂

λ₂ < Υ{λ) = 0 < λ3

< Y{A} = 0.186 λ + Ε < Λ₄

where λ = 380 nm a d where C = 42.7 ± 12.5

A₂ = 445 nm D =163.7 ± 12.5

A₃ = 635 nm E = -62.3 ± 12.5

A ■=^' 780 nm

3. A spectrally selective mirror according to claim 1 , wherein having a reflectance spectrum within a region bound by the following equations, where Υ(λ) is a measure of the reflectance at a driver's viewing angle (%} at wavelength λ (nm):

λ| < Υ(Λ) = -0.272 A + D < A₂

λ₂≤ Y(A} = C≤ A₃

As≤Υ(λ) = 0.166 λ + Ε λ4

where λι ~ 380 nm and where C = 42.7 ± 10

A₂ = 445 m D =183.7 ± 10

λ₃ = 635 nm E = -62.3 ± 10

A.4 = 780 nm

4. A spectrally selective mirror according to claim 1., wherein having a reflectance spectrum within a region bound b the foliowing equations, where Y(A) is a measure of the reflectance at a drivers viewing angle (%) at wavelength λ (nm):

λι < Υ(λ) = -0.272 A + D < λ₂

A₂ < Υ(λ) = C < A₃

A_g Y{A} = 0.166 λ + E < A₄

where λι = 380 nm a d where C = 42.7 ± 5

A₂ ^~ 445 nm D =163.7 ± 5

A₃ = 635 nm E = -62.3 ± 5

- 780 nm

5. A spectrally selective mirror according to claim 1 , wherein having a reflectance spectrum within a region bound by the following equations, where Υ(λ) is a measure of the reflectance at a driver's viewing angle (%} at wavelength λ (nm):

A, < Υ(λ.) = -0.272 A + D < A₂

λ₂≤ Y(A} = C≤ λ₃

As≤Υ(λ) = 0.166 λ + Ε λ4

where As 380 nm and where C ~ 42.7 ± 2.5

A₂ 445 nm D =163.7 ± 2.5

λ₃ 635 nm E = -62.3 ± 2.5

λ₄ 780 nm

6. A spectrally selective mirror according to any one of claims 1 to 5, wherein the mirror exhibits a Colour Rendering Index (CRI) of at least 80.

7. A spectrally selective mirror according to any one of claims 1 to 6, wherein the spectrum has been optimised to exist at a discrete angle/angles, or across a range of driver's viewing angle between 0 and 90 degrees.

8. A spectrally selective mirror according to any one of claims 1 to 7, wherein the average Disability Glare improvement on standard glass mirror coated with chrome is greater than 10%.

9. A spectrally selective mirror according to any one of claims 1 to 8, wherein the mirror includes a substrate having a coating thereon.

10. A spectrally selective mirror according to claim 9, wherein the coating is a multi-layered interference coating.

11. A spectrally selective mirror according to claim 10, wherein the coating includes at least three alternating layers, with adjacent layers having different refractive indices.

12. A spectrally selective mirror according to claim 11. wherein adjacent layers alternate between a relatively high and a relatively low refractive index.

13. A spectrally selective mirror according to any one of claims 10 to 12, wherein the multi-layered interference coating includes at least three layers and has opposed outermost layers, either one or two innermost layers (one where the numbe of layers in the coating is odd and two where the number of layers in the coating is even), and an even number of intermediate layers between an outermost layer and the innermost layers, wherein the optical thickness of the outermost layers is less tha the optical thickness of the innermost layers, and the optical thickness of each layer increases from one layer to the next layer, in a manner such that the innermost layers have the largest optical thickness.

14. A spectrally selective mirror according to any one of claims 10 to 13, wherein each layer of the multi-layered interference coating has an optical thickness in the range of about 0.013 to about 1.058, more preferably in the range of from about 0.026 to about 0.899, and most preferably in the range of about 0.029 to 0.767. 5. A spectrally selective mirror according to any one of claims 10 to 14, wherein the multi-layered interference coating includes five layers, having opposed outermost layers, one innermost layer, and two intermediate layers, on each between an outermost layer and the innermost layer, wherein the outermost layers have an optical thickness in the range of about 0.013 to about 0.794_., the intermediate layers have an optical thickness in the range of about 0.029 to about 0.461 , and the innermost layer has an optical thickness of about 0.265 to about 1.058.

18. A spectrally selective mirror according to any one of claims 10 to 14, wherein the multi-layered interference coating includes five layers, having opposed outermost layers, one innermost layer, and two intermediate layers, one each between an outermost layer and the innermost layer, wherein the outermost layers have an optical thickness in the range of about 0.028 to about 0.132, the intermediate layers have an optical thickness in the range of about 0.058 to about 0.238, and the innermost layer has an optical thickness of about 0.681 to about 0.899. 7. A spectrally selective mirror according to any one of claims 10 to 14, wherein the multi-layered interference coating includes five layers, having opposed outermost layers, one innermost layer, and two intermediate layers, one each between an outermost layer and the innermost layer, wherein the outermost layers have an optical thickness in the range of about 0.029 to about 0.056, the intermediate layers have an optical thickness in the range of about 0.121 to about 0.248, and the innermost layer has an optical thickness of about 0.714 to about 0.787.

18. A spectrally selective mirror according to any one of claims 10 to 17, wherein there is a refractive index contrast between adjacent layers of the multi-layered interference coating, the contrast achieved by selection of materials with different refractive indices for adjacent layers.

19. A spectrally selective mirror according to claim 18, wherein the refractive index contrast is achieved by layers of materials with high refractive index adjacent to layers of materials with low refractiv index, a high refractive index material being selected from the group including chromium, aluminium, titanium, nickel, molybdenum, zirconium, tungsten, silicon, niobium, tantalum, vanadium, cobalt, manganese, silver, zinc, and mixtures thereof; and an oxide, nitride, boride, fluoride or carbide thereof, and mixtures thereof, and a low refractive index material being selected from the group including boron, silicon, germanium, antimony, tellurium, polonium, niobium, zirconium, magnesium, fin, tantalum, aluminium, chromium, titanium and mixtures thereof, and an oxide, nitride, boride, fluoride or carbide thereof, and mixtures thereof.

20. A spectrall selective mirror according to claim 9, wherein at least one of the layers of low index refractive material is a layer formed from Si02.

21. A spectrally selective mirror according to claim 19 or claim 20, wherein at least one of the layers of high index refractive material is a layer formed from chromium, or a chromium mixture, such as€r-Zr, Cr-Ni or Cr~Mo_s or carbides or nitrides thereof, such as Cr-N.

22. A spectrally selective mirror according to any of claims 9 to 21, wherein the substrate is a metal, a glass, or a polymeric or plastic material, or blends thereof,

23. A spectrally selective mirror according to claim 22, wherein the substrate Is a plastic substrate formed from a material selected from the group including poiyacryiate, polyester, polystyrene, polyethylene, polypropylene, polyamides, polyamides, polycarbonate, epoxy, phenolic, acrylonitrile-butadiene-sfyrene, acrylonitrile-styrene-acrylates, acetal and blends of thereof.

24. A spectrally selective mirror according to claim 22, wherein the substrate is a glass substrate formed from a material selected from the group including silica, soda lime glass, porosilicaie glass, fused silica glass, lead-oxide glass, oxide glass, aluminosilicate glass, or blends thereof.

25. A spectrally selective mirror according to claim 22, wherein the substrate is a metal substrate formed from a material selected from the group including aluminium, boron, chromium, cobalt, copper, iron, magnesium, molybdenum, nickel, niobium, stainless steel, tantalum, tin titanium, tungsten, vanadium, zinc, zirconium and mixtures thereof; and an oxide, nitride, bonde or carbide thereof, and mixtures thereof.