WO2008110963A1

WO2008110963A1 - Phototherapy apparatus for treatment of skin disorders

Info

Publication number: WO2008110963A1
Application number: PCT/IB2008/050799
Authority: WO
Inventors: Georg Henninger
Original assignee: Philips Intellectual Property & Standards Gmbh; Koninklijke Philips Electronics N. V.
Priority date: 2007-03-09
Filing date: 2008-03-05
Publication date: 2008-09-18

Abstract

The present invention relates to a phototherapy apparatus, which can be used for phototherapeutic treatment of certain skin disorders, particularly for the treatment of acne. The apparatus comprises an incandescent lamp comprising an optical interference filter coating attached thereto. The coating is comprised of a plurality of alternating high and low refractive index layers (H, L), said coating having a spectrally broad low transmission of less than 50% average in the UV wavelength range between 300 and 380 nm, a steep increase of transmission between 380 and 400 nm, a spectrally narrow high transmission of 90 to 100 % average at a blue wavelength range from 400 nm to 450 nm, a steep decrease of transmission between 450 and 460 nm, a transmission below 20 % average in the wavelength range from 460 to 570 nm, a steep increase of transmission between 570 and 580 nm, a spectrally narrow high transmission of 80 to 100 % average in the red wavelength range from 580 to 700 nm, and a transmission less than 20 % average in the IR wavelength range between700 and 1800 nm. The apparatus provides a dual narrow band radiation spectrum in the blue and red wavelength range that fights bacteria growth and stimulates skin regeneration. The invention also relates to an incandescent lamp useful for treatment of certain skin disorders, particularly of acne.

Description

PHOTOTHERAPY APPARATUS FOR TREATMENT OF SKIN DISORDERS

TECHNICAL FIELD OF THE INVENTION

The invention relates to a phototherapy apparatus for phototherapeutic treatment of certain skin disorders, particularly for the treatment of acne. BACKGROUND OF THE INVENTION

Acne is the most common of skin disorders that are associated with the activity of sebaceous oil glands. Acne is thought to be caused by the obstruction of sebaceous oil glands by a mixture of excess sebum and epithelial cells from the glands' walls. Propionibacterium acnes (P. acnes) and other naturally present bacteria can proliferate in the mixture of sebum and epithelial cells. The chemical breakdown of sebum by bacterial action then releases free fatty acids, which in turn trigger an inflammatory reaction producing the typical acne scars.

There are several known techniques for reducing or eliminating such skin disorders, treatment with antibiotics or hormones being the mainstream therapy. However, there is a concern that treatment with antibiotics may cause resistance; treatment by hormone therapy may cause side effects. Therefore phototherapy has been found to be a useful alternative. Particularly a phototherapeutic treatment using blue (wavelength 415 nm) and red (wavelength 700 nm) light has been reported as being especially effective. Blue light with a wavelength range from 400 to 450 nm stimulates the production of activated oxygen within the clogged skin pores. Activated oxygen fights bacteria growth, thus the blue light has an antibacterial effect and eliminates the cause of infection within the pore.

Red light having a wavelength range from 580 to 659 nm initiates healing, as well as relaxation of the tissue and it promotes blood flow. The inflammation can fade away faster and the skin is in a position to regenerate. From US 2006/0030908 a phototherapy device is known, comprising at least one bi-color light emitting diode that emits a range of wavelengths in a blue portion of the visible electromagnetic spectrum and a range of wavelengths in a red portion of the visible electromagnetic spectrum. Such device comprising one or more light emitting diodes is useful for treatment of small skin areas, e.g. a single inflamed blackhead. But to reach the power needed for an effective treatment of a larger body area, a lot of LEDs must be used. This may make the cost for such device too high for a consumer application.

SUMMARY OF THE INVENTION

The present invention provides a phototherapy apparatus for treatment of skin disorders comprising an incandescent lamp coated with an optical interference filter coating, said optical interference filter coating covering at least a portion of a surface of the vessel of said lamp, said coating being comprised of a plurality of alternating high and low refractive index layers (H, L), said coating having a spectrally broad low transmission of less than 50% average in the UV wavelength range between 300 and 380 nm, a steep increase of transmission between 380 and 400 nm, a spectrally narrow high transmission of 90 to 100 % average at a blue wavelength range from 400 nm to 450 nm, a steep decrease of transmission between 450 and 460 nm, a transmission below 20 % average in the wavelength range from 460 to 570 nm, a steep increase of transmission between 570 and 580 nm, a spectrally narrow high transmission of 80 to 100 % average in the red wavelength range from 580 to 700 nm, and a transmission less than 20 % average in the IR wavelength range between 700 and 1800 nm. Such a phototherapy apparatus will provide effective phototherapeutic treatment of large inflamed skin areas at reasonable cost.

The lamp comprising the optical interference filter coating according to the invention is a single source type providing two different spectral emission bands concentrated in the blue and red range of the visible light and allows for optimal red/blue light phototherapy.

The effects of blue and red irradiation on the inflamed area are biologically dependent on each other. In terms of therapeutic value, the two types of radiation are complementary. Therefore by combining it in a single unit, it is possible to achieve an enhanced therapeutic effect without increasing the incidence of erythematic and thermal damage. It is a particular advantageous feature of the apparatus according to the invention, that the optical interference filter is designed to transmit only red and blue light, emitted by the incandescent lamp, while it reflects IR- as well as UV-radiation. The filter eliminates wavelengths below 380 nm, which are known to cause erythema, while providing little therapeutic benefit. The filter also eliminates IR radiation that causes further dilation of blood vessels in the inflamed skin area.

This feature makes the treatment especially comfortable for the patient. As the radiation does comprise no or very little radiation in the UV-range and IR range, even prolonged exposure does not cause uncomfortable heat or sunburn.

A positive side effect of the reflection of unwanted radiation back to the filament of the incandescent lamp is saving of energy that is otherwise required to maintain the lamp filament at operating temperature.

Thus the apparatus is useful for a dual-band phototherapy for the treatment of skin disorders, particularly for the treatment of acne and related skin disorders for personal health care. As only a small number of incandescent lamps is necessary to provide a large area treatment, the apparatus can be manufactured at low cost.

According to a preferred embodiment of the invention the optical interference filter coating comprises at least three multi-periods, spectrally adjacent stacks comprising a plurality of alternating high and low refractive index layers (H, L). Example given, the interference filter coating may have the following general structure A*A* B *M^aC*N^a, wherein K denotes a stack of structure (L/aHL/a); M denotes a stack (L/bHL/b) and N denotes a stack (L/cHL/c), and wherein 1.4 < A < 1.7; 0.5 < B < 1.0 and 0.7 ≤ C < 1.0; a = 2; b = 1; c = 2; 0 < k < 8; 0 < m < 10 and O <n < 8 at a reference wavelength λ between 925 and 975 nm, preferably at 950 nm. According to a second example the interference filter coating has the general structure A* A* B¹^M"¹ CW¹, wherein K denotes a stack of structure (L/aH/a'L/a"HL/a"H/a'L/a); M denotes a stack (L/bHL/b) and N denotes a stack (L/cHL/c), wherein 0.8 < A < 1.7; 0.6 < B < 1.6; and 0.6 < C < 1.1; a = 3, a' = 10, a" = 10, b=l and c = 2; 0 < k ≤ 8; 0 < m < 10 and 0 <n < 8 at a reference wavelength λ between 925 and 975 nm, preferably at 950 nm. Typically the material of the first layer (L) having the low refractive index comprises silicon dioxide or aluminum oxide or mixtures or composites thereof and the material of the second layer (H) having the high refractive index is chosen from the group formed by titanium oxide, zirconium oxide, hafnium oxide, niobium oxide, tantalum oxide, silicon nitride or mixtures or composites thereof. Said optical interference filter coating may be arranged on the inner or outer surface of the lamp vessel.

According to a preferred embodiment of the invention said incandescent lamp is an incandescent halogen lamp containing halogen gas or a halogen compound in the lamp vessel. Typically the apparatus will comprise a reflector of a shape known in the art, example given, a cylindrical or a generally parabolic shape.

The apparatus may comprise an additional UV-filter, to comply with UV- free safety level requirements.

The invention also relates to an incandescent lamp coated with an optical interference filter coating, said optical interference filter coating covering at least a portion of a surface of the vessel of said lamp, said coating being comprised of a plurality of alternating high and low refractive index layers (H, L), said coating having a spectrally broad low transmission of less than 50% average in the UV wavelength range between 300 and 380 nm, a steep increase of transmission between 380 and 400 nm, a spectrally narrow high transmission of 90 to 100 % average at a blue wavelength range from 400 nm to 450 nm, a steep decrease of transmission between 450 and 460 nm, a transmission below 20 % average in the wavelength range from 460 to 570 nm, a steep increase of transmission between 570 and 580 nm, a spectrally narrow high transmission of 80 to 100 % average in the red wavelength range from 580 to 700 nm, and a transmission less than 20 % average in the IR wavelength range between 700 and 1800 nm. BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows an exploded view of an embodiment of apparatus according to the invention.

Fig. 2 is a cross-sectional view taken on line Ha-IIa of Fig. 1 of an embodiment comprising an additional UV-filter plate.

Fig. 3 is a graphical representation of the transmission curve between 300 and 2000 nm of a filter according to a first embodiment of the invention (Filter A).

Fig. 4 is a graphical representation of the transmission curve between 300 and 2000 nm of a filter according to a second embodiment of the invention (Filter B).

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to an apparatus, which can be used for phototherapeutic treatment of certain skin disorders. Specifically, the present invention can be used for the treatment of acne and related skin disorders. Fig. 1 shows a typical embodiment of the phototherapy apparatus 1 for treatment of skin disorders according to the invention, with a housing 2 in which a radiation source is present which in this embodiment comprises two incandescent halogen lamps 33.

As evident, the number of lamps in the apparatus can be chosen at will to affect the area of treatment and may vary, depending on the desired application. Two lamps in a housing are ideal to treat the total upper body area of a person. A single lamp in a desk apparatus may be sufficient to treat all or part of the face area.

Besides one or more incandescent lamp the apparatus may include a lamp fixture, which can be moved and directed to the treated patent specific skin area at an adjustable distance relative to the patient's treated skin area.

The apparatus may further comprise a control board to control lamp power, illumination duration, general on/off and mains control functions and other auxiliary components known in the art.

An incandescent lamp to be used for the purpose of the present invention is preferably a light source with a high flux density, such as an incandescent tungsten halogen lamp.

Such lamps are of conventional construction and are generally constructed of a tube, which forms a lamp vessel that encloses an elongated, tungsten filament. The lamp vessel is filled in a known way with an inert gas mixture, comprising a halogen additive According to a preferred embodiment of the present invention the material of the lamp vessel consists of an UV- blocking glass.

The tungsten filament is connected at both ends to current supply conductors which each comprise an inner lead connected to a molybdenum foil in the pinch sealed portion of the lamp vessel, and an outer lead.

The lamp vessel preferably has an elliptically shaped mid-portion which is provided with an interference filter according to the invention on the inside or outside of the lamp envelope, thereby reflecting part of the radiation back toward the filament to achieve the desired dual- band spectral emittance and also to improve thermal efficiency and reduce the power necessary for incandescence.

As the light output is spread along the incandescent filament, a useful alternative to an elliptical bulb, specifically for large area treatment, may be an elongated filament in an elongated cylindrical rod-shaped lamp vessel, known as "halogen rod".

One preferred embodiment of the invention relates to an apparatus comprising a reflector 2, which causes the flux to be emitted over a narrower segment of the circumference, for example 140°, instead of through the entire 360°circumference of the lamp.

The fixture of the lamp within the reflector may be adjustable from a relatively narrow, "spot" type beam to a relative broad "flood"-type beam.

The reflector body consists of a reflective metal or comprises a reflective coating. The reflector coating typically comprises aluminum, though the reflector coating can also comprise silver, gold, white gold, chromium or any other suitable reflective material. For treatment of larger body parts the reflector body is preferably shaped as a cylinder, as shown in Fig. 1. For treatment of the face or parts thereof part a parabolic aluminized reflector lamp (PAR) may be suited. Ideally, a PAR lamp comprises a completely parabolic-shaped reflector, which is coated with a reflective substance. The typical effective illumination output energy of incandescent halogen or xenon lamps is relatively high and is in the order often to hundreds of watts. This energy level of the radiation source, when properly collected and directed by the optical reflector or by other means of optical light collection, can generate an energy output flux having a typical flux value in the range of 10 to 500 mW/cm square on any spot of the treated skin. This energy flux range is high enough to facilitate an effective phototherapeutic effect on an entire human face or body part, typically over 400 cm square in area.

An incandescent halogen lamp in operation generally produces a continuous spectrum of radiation from the UV- range below 300 nm to the IR-range up to 2600 nm.

The required dual narrow spectral emission band of the phototherapy apparatus according to the invention is due to an optical interference filter that provides two band pass areas in the blue and in the red range of the electromagnetic spectrum.

A "spectrally narrow wavelength range" refers to a wavelength range of a width below 100 nm; a" spectrally broad wavelength range" refers to a wavelength range of a width above 100 nm.

According to the invention the optical interference filter is provided as a coating attached to the lamp vessel for easy assemblage and handling of the apparatus. The radiation originating from the radiation source is thus transmitted through the interference filter.

All spectral intervals of the light source emission outside the blue (400 and 450 nm) and the red (580 and 700 nm) range are reflected and filtered out to match the emitted spectrum to the therapeutic requirements and to reduce unwanted thermal and UV load to the epidermis. The upper limit of the red wavelength range is determined from the observation that wavelengths in the range from 700 to 900 nm have a strong heating effect on the skin, while not contributing significantly to the treatment. The lower limit of the blue wavelength range is determined from the observation that wavelength in the range from 300 to 380 nm aggravates acne lesions.

All radiation beside the blue and red range is reflected back to the lamp filament and reconverted to radiation in the visible portion of the electromagnetic spectrum, thereby greatly increasing the luminous efficiency of the lamp. As a result, nearly all radiation emitted by the incandescent lamp is phototherapeutic light absorbed by the patient.

In a preferred embodiment of the invention either the reflector or the lamp housing may be covered by a cover plate comprising an additional UV-filter (4) to ensure that the illumination flux in the UV range is less than 0.1 microwatt/cm square in the spectral range of 200 to 400 nm, to comply with UV-free safety level requirements.

The optical interference filter according to the invention is preferably designed in thin film technology. A thin film optical interference filter coating for selectively reflecting and transmitting different portions of the electromagnetic spectrum comprises a plurality of alternating layers of a low refractive index material (represented by L) and a high refractive index material (represented by H).

As material for optical interference filters use is often made of refractory metal oxides having high and low indexes of refraction. Refractory metal oxides are used because they are able to withstand the relatively high temperatures, example given 400° C to 900° C, which develop during lamp operation.

Materials that can be advantageously used for the highly refractive sublayers H include titanium oxide (TiO₂), zirconium oxide (ZrO₂), hafnium oxide (HfO₂), niobium oxide (Nb₂Os), tantalum oxide (Ta₂Os) and silicon nitride (S13N₄) and physical mixtures and multilayer arrangements thereof. Silicon oxide (SiO₂) or aluminum oxide (Al₂Os) and physical mixtures and multilayer arrangements thereof may be preferably used for the lowly refractive sub-layers L.

Applying a coating to the interior and/or exterior surfaces of incandescent lamp 33 is accomplished in a simple manner employing a low pressure vapor deposition (LPCVD) coating process for applying alternating layers of high and low refractive index materials. In an LPCVD process a suitable metal oxide precursor reagent or reagents for each material of the film is separately introduced into a decomposition chamber wherein it is decomposed or reacted to form the metal oxide on a heated substrate. Separate layers of, for example, silicon oxide and niobium oxide are applied onto the substrate in this fashion until the desired filter is achieved. Such chemical vapor deposition techniques are well known to those skilled in the art. Another process that is possible to employ to apply an optical interference coating in a uniform manner to all of the interior surfaces of a lamp envelope is an aqueous process that is also known to those skilled in the art. However, in an aqueous process the coating materials must be alternatively applied by spraying or dipping along with spinning and baking or drying in order to achieve uniform coating thicknesses and to enable successive alternating layers to be built up to obtain the film without diffusion of one material into the other. This process is extremely difficult to apply uniformly to a lamp envelope and is very time consuming. Consequently, an LPCVD or chemical vapor deposition (CVD) process employing a suitable reagent in gaseous form that is decomposed on the surface of the substrate to be coated is the present state of technology preferred as the method to apply the optical interference coating to the interior and/or exterior surfaces of the lamp.

Alternatively, physical vapor deposition (PVD) processes are well suited to the mass production of optical interference coating, because this type of process is compatible with thickness monitoring and automated control techniques. Physical vapor deposition is a process in which material vaporized from a solid source is transported in the gas phase through a vacuum or low pressure gaseous or plasma environment and subsequently condensed onto a substrate. Vacuum deposition by thermal resistive or arc evaporation, magnetron sputtering, and ion plating techniques are PVD processes.

The thicknesses of the layers are determined by the "quarterwave stack" principle.

According to the "quarterwave stack principle", optical interference coatings are based on a reflectance stack consisting of alternating layers of high and low index films, each layer having an optical thickness of one Quarter- Wave Optical Thickness (QWOT). The optical thickness is defined as the product of the physical thickness times the refractive index of the film. The QWOT is referenced to a conveniently chosen design wavelength. For example, at a design wavelength according to the invention of 950 nm, the QWOT of silicon dioxide typically has a physical thickness of 163.7 nm.

The thickness of the sub-layers should be uniform and accurately held to achieve the best effect according to the invention. Nevertheless deviations of individual layer thicknesses occur and do not hamper the functionality of the filter as intended by this invention, as these filters have some tolerance to layer thickness variations.

As a single reflectance stack reflects only across one portion of the electromagnetic spectrum, three or more multiperiod, spectrally adjacent stacks, each comprising a plurality of alternating high and low refractive index layers (H, L), are combined for the dual transmission bands across the visible spectrum.

Such a three multiperiod filter stack is represented in the following manner, whereby the notation is known to those skilled in the art:

The stack structure is generally denoted by A* AT^k B^=Af CW¹.

According to a first embodiment K denotes a stack of structure (L/aHL/a); M denotes a stack (L/bHL/b) and N denotes a stack (L/cHL/c); wherein 1.4 < A < 1.7; 0.5 < B < 1.0 and 0.7 < C < 1.0; a = 2; b = 1; c = 2; 0 < k < 8; 0 < m < 10 and 0 <n < 8 at a reference wavelength λ between 925 and 975 nm, preferably at 950 nm.

According to a second embodiment K denotes a stack of structure (L/aH/a'L/a"HL/a"H/a'L/a); M denotes a stack (L/bHL/b) and N denotes a stack (L/cHL/c), wherein 0.8 < A < 1.7; 0.6 < B < 1.6; and 0.6 < C < 1.1; a = 3, a' = 10, a" = 10, b=l and c = 2; 0 < k ≤ 8; 0 < m < 10 and 0 <n < 8 at a reference wavelength λ between 925 and 975 nm, preferably at 950 nm.

Layers forming a period are surrounded by brackets, with the superscripts 1, n and m being the number of times the period is repeated in the stack. A, B and C are empirical factors, with which every individual layer thickness has to be multiplied, whereby the individual factors for every layer may vary within the ranges given for A, B and C. A suitable choice of A, B and C will fine-tune the filter design with regard to position and slope of the filter edges.

The values for the denominators a, a, a", b and c are chosen based upon the required optical thickness T₀ of each layer according to the formula: T₀

=λ/(4 x denominator), wherein λ is the reference wavelength. The physical thickness T_p of each layer is equal to the optical thickness T₀ divided by the index of refraction of the material, multiplied by the reference wavelength.

Accordingly, the notation L/a represents a fraction of a quarterwave of "optical thickness" of the L material at the reference wavelength, i.e., one- half of a quarterwave (1/8 wave) for a =2.

The sequence of the stacks can be exchanged and further stacks can be added to narrow the bandwidth of the pass band.

Further stacks are preferably added in the IR region. For example, a long wave-pass stack with blocking features in the near- IR region next to the visible region can be added. It shifts the transmission pass region to higher wavelengths. Otherwise a further short wave-pass filter can be added to increase the amount of far-IR radiation reflected by the filter.

According to one embodiment of the invention the highly refractive sublayers in themselves are composed of a sub-stack of two layers of a first highly refractive material and a thin intermediate layer of a second highly refractive material to separate the two layers of the first material. The thickness of the intermediate layer is preferably in the range from 1 to 25 nm. This intermediate layer will avoid extended crystal growth in the highly refractive layer.

How many times the various stacks K, M and N are repeated, in other words the choice for the exponents k, n and m is determined on the basis of an analysis of the maximum increase of the reflectance per thickness increase of the filter design. Analysis has shown that it is very favorable to choose values for k, n and m as 0 < k < 8; 0 < m < 10 and 0 <n < 8 if a high reflectance is desired. A further increase of the values for k, m and n generally has the disadvantage that the width of the transmission window decreases. Such decrease is also undesirable because it causes the tolerance of the filter design with respect to variations in layer thickness occurring during the manufacturing process of the interference film to be reduced.

If another reference wavelength is chosen the denominators a, a', a", b and c must be adapted accordingly to reach the same result for every one of the stacks given.

In the case the order of the stacks is to be interchanged it is preferred that the outermost layer next to ambient is chosen to be of the low index material layer L and that in case the outermost layer is not a low index material layer L such a layer is added to the filter design.

In a particularly preferred form of the invention, the high index of refraction material will comprise tantalum oxide and the low index of refraction material is comprised of silicon oxide.

According to an specific embodiment an optical interference filter comprising alternating layers of Siθ2 and Ta₂Os were applied to the outer surface of the envelope of a tungsten-halogen incandescent lamps of the type illustrated in FIG. 1, employing an LPCVD coating process according to the computer optimization set forth in Table 1 for a total of forty-seven alternating layers Of SiO₂ and Ta₂Os.

According to a first specific embodiment a filter A is designed as a 35 layer coating of the design type: 1.48(0.5LH0.5L)⁵ /0.72(LHL)⁷ZO-SO(O-SLHO-SL)⁵.

According to a second special embodiment a filter B is designed as a 55 layer coating of the design type:

1.48(0.3L0.1H0.1LH0.1L0.1H0.3L)⁵/0.72(LHL)⁷/0.86(0.5LH0.5L)⁵.

The following Table I specifies the filter designs A and B, i.e. layer structure, the number of layers, physical thickness of each layer and layer materials of the optical interference band pass filter with a dual pass band transmission in the blue and red visible range. Layer thicknesses are set forth in nanometers.

Table 1 : Layer Material Filter A Filter B

1 SiO2 50.0 50.0

2Ta2O5 174.3 31.3

3 SiO2 256.9 25.3

4Ta2O5 171.6 49.6

5 SiO2 250.9 20.6

6Ta2O5 166.7 36.8

7 SiO2 253.2 269.1

8Ta2O5 168.6 185.6

9 SiO2 249.1 35.6

10Ta2O5 172.5 24.4

11 SiO2 237.8 23.9

12Ta2O5 83.1 23.7

13 SiO2 222.5 278.2

14Ta2O5 89.0 40.7 15 S1O2 231.8 11.5

16Ta2O5 91.6 106.8

17 S1O2 235.1 255.8

18Ta2O5 94.3 163.1

19 S1O2 215.9 259.5

20Ta2O5 95.6 158.3

21 SiO2 249.3 258.6

22Ta2O5 101.6 166.4

23 SiO2 194.8 252.1

24Ta2O5 98.1 114.1

25 SiO2 248.3 15.5

26Ta2O5 102.3 31.7

27 SiO2 161.0 257.9

28Ta2O5 89.7 173.9

29 SiO2 138.3 246.3

30Ta2O5 91.7 78.9

31 SiO2 128.1 248.8

32Ta2O5 93.2 93.4

33 SiO2 152.5 44.8

34Ta2O5 83.5 13.6

35 SiO2 63.6 162.1

36Ta2O5 - 81.4

37 SiO2 246.3

38Ta2O5 87.5

39 SiO2 217.6

40Ta2O5 93.5

41 SiO2 253.9

42Ta2O5 101.1

43 SiO2 193.3

44Ta2O5 100.3

45 SiO2 248.8

46Ta2O5 102.5

47 SiO2 161.6

48Ta2O5 87.1

49 SiO2 136.6

50Ta2O5 97.4

51 SiO2 130.2

52Ta2O5 83.6

53 SiO2 158.4

54Ta2O5 89.5

55 SiO2 53.3

Fig. 3 and 4 depict the transmission characteristics of the optical interference filter of Table 1. Fig. 3 and 4 are spectral graphs, in which the radiation intensity of the lamps comprising filter A or B in relative units (%) is plotted as a function of the wavelength in nm of the radiation. Filter B (Fig. 4) transmits even less radiation in the yellow to green range of the visible spectrum and in the IR range from 700 to 1600 nm in comparison to filter A (Fig. 3).

The transmission characteristics covers the range from 300 to 2000 nanometers, which is generally the range from the near UV to the far IR range including the visible range from 400 to 700 nm. Referring to FIG. 3 and 4, it is interesting to note that in accordance with the present invention, most UV- and IR radiation is minimized as much as possible in order to provide a good therapeutic light. To express this in another way, the available energy is concentrated in the blue and red regions of the visible spectrum in order to achieve the best possible efficiency of light generation (i.e. lumens per watt) commensurate with good therapeutic efficiency.

The ratio of emission in the blue wavelength range in relation to the emission in the red wavelength range may be adapted by changing the wattage of the lamp. Higher wattage means more emission in the blue area, low wattage means more wattage in the red area. The apparatus may additionally comprise a separate UV-filter 4, as shown in Fig. 2.

Although the present invention is illustrated in connection with specific embodiments for instructional purposes, the present invention is not limited thereto.

Various adaptations and modifications may be made without departing from the scope of the invention. Therefore, the spirit and scope of the appended claims should not be limited to the foregoing description.

Claims

CLAIMS:

1. A phototherapy apparatus (1) for treatment of skin disorders comprising an incandescent lamp (33) coated with an optical interference filter coating, said optical interference filter coating covering at least a portion of a surface of the vessel of said lamp, said coating being comprised of a plurality of alternating high and low refractive index layers (H, L), said coating having a spectrally broad low transmission of less than 50% average in the UV wavelength range between 300 and 380 nm, a steep increase of transmission between 380 and 400 nm, a spectrally narrow high transmission of 90 to 100 % average at a blue wavelength range from 400 nm to 450 nm, a steep decrease of transmission between 450 and 460 nm, a transmission below 20 % average in the wavelength range from 460 to 570 nm, a steep increase of transmission between 570 and 580 nm, a spectrally narrow high transmission of 80 to 100 % average in the red wavelength range from 580 to 700 nm, and a transmission less than 20 % average in the IR wavelength range between 700 and 1800 nm.

2. A phototherapy apparatus according to claim 1, wherein the optical interference filter coating comprises at least three multi-period, spectrally adjacent stacks comprising a plurality of alternating high and low refractive index layers (H, L).

3. A phototherapy apparatus according to claim 2, characterized in that the interference filter coating has the following general structure A* I^ B* M"¹ C* N^{^}, wherein K denotes a stack of structure (L/aHL/a); M denotes a stack (L/bHL/b) and N denotes a stack (L/cHL/c), and wherein 1.4 < A < 1.7; 0.5 < B < 1.0 and 0.7 < C < 1.0; a = 2; b = l; c = 2; 0 < k < 8; 0 < m < 10 and 0 <n < 8 at a reference wavelength λ between 925 and 975 nm, preferably at 950 nm.

4. A phototherapy apparatus according to claim 2, characterized in that the interference filter coating has the following general structure A* A* B^M"¹ CW¹, wherein AT denotes a stack of structure (L/aH/a'L/a"HL/a"H/a'L/a); M denotes a stack (L/bHL/b) and N denotes a stack (L/cHL/c), wherein 0.8 < A < 1.7; 0.6 < B < 1.6; and 0.6 < C < 1.1; a = 3, a' = 10, a" = 10, b=l and c = 2; 0 < k < 8; 0 < m < 10 and 0 <n < 8 at a reference wavelength λ between 925 and 975 nm, preferably at 950 nm.

5. A phototherapy apparatus as claimed in claim 1, characterized in that the material of the first layer (L) having the low refractive index comprises silicon dioxide or aluminum oxide or mixtures or composites thereof.

6. A phototherapy apparatus as claimed in claim 1, characterized in that the material of the second layer (H) having the high refractive index is chosen from the group formed by titanium oxide, zirconium oxide, hafnium oxide, niobium oxide, tantalum oxide, silicon nitride or mixtures or composites thereof.

7. A phototherapy apparatus according to claim 1, wherein said optical interference filter coating arranged on the inner or outer surface of the lamp vessel.

8. A phototherapy apparatus according to claim 1, wherein said incandescent lamp is an incandescent halogen lamp containing halogen gas or a halogen compound in the lamp vessel.

9. A phototherapy apparatus according to claim 1, wherein the apparatus comprises a reflector (3).

10. An incandescent lamp (33) coated with an optical interference filter coating, said optical interference filter coating covering at least a portion of a surface of the vessel of said lamp, said coating having a spectrally broad low transmission of less than 50% average in the UV wavelength range between 300 and 380 nm, a steep increase of transmission between 380 and 400 nm, a spectrally narrow high transmission of 90 to 100 % average at a blue wavelength range from 400 nm to 450 nm, a steep decrease of transmission between 450 and 460 nm, a transmission below 20 % average in the wavelength range from 460 to 570 nm, a steep increase of transmission between 570 and 580 nm, a spectrally narrow high transmission of 80 to 100 % average in the red wavelength range from 580 to 700 nm, and a transmission less than 20 % average in the IR wavelength range between 700 and 1800 nm.