WO2010016009A1

WO2010016009A1 - Ultra-violet and visible light emitting system

Info

Publication number: WO2010016009A1
Application number: PCT/IB2009/053397
Authority: WO
Inventors: Maurice A. H. Donners; Gerardus A. R. Van Dijk; Lucas J. M. Schlangen; Maarten M. J. W. Van Herpen; Oscar H. Willemsen; Michel C. J. M. Vissenberg; Marcellinus P. C. M. Krijn; Tim Dekker
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2008-08-07
Filing date: 2009-08-05
Publication date: 2010-02-11
Also published as: TW201017713A

Abstract

A UV-VIS light emitting system is described. The system comprises a phosphor mixture emitting within the UVB and the visible range of the electromagnetic spectrum. The system has an efficiency of 84 lm/W or larger and a spectral power distribution E(λ) such that the ratio Ǫ between the dose rate for vitamin D synthesis R _D = ∫E{λ)A _D (λ)dλ and the luminous flux Φ = ∫E{λ)V (λ)dλ is 10^-6 J/m²lms or larger. The UV-VIS light emitting system is therefore suitable for general lighting applications while providing controlled stimulation of vitamin D synthesis.

Description

Ultra-violet and visible light emitting system

FIELD OF THE INVENTION

The invention relates to a combined ultra-violet and visible (UV-VIS) light emitting system and, in particular, though not exclusively, to a UV-VIS light emitting system for stimulating vitamin D synthesis and a UV-VIS phosphor blend for use in such system.

BACKGROUND OF THE INVENTION

It is commonly known that vitamin D plays an important role in the human calcium metabolism and skeletal health. In addition, it has been recognized to provide many further beneficial health effects, such as a protective effect against colon, prostate, breast and prostate cancer, hypertension and the prevention of certain autoimmune diseases such as multiple sclerosis and type I diabetes. Hence, an increase of the recommended daily intake (RDI) ranging between 1000 IU and 4000 IU per day has been proposed in order to secure all the potential benefits of vitamin D. Vitamin D is synthesized in the skin after exposure to UVB radiation and because only few sorts of food contain vitamin D, most people gain their vitamin D intake from sunlight exposure. Many populations and age groups of people however are exposed too little or too short to natural daylight. As a consequence many people suffer from low vitamin D levels. An increase in controlled exposure to moderate UVB levels is therefore desirable. Several definitions of the subdivisions of the electromagnetic spectrum into ultraviolet and visual ranges exist. In this application, the wavelength ranges are chosen as: UVB between 280 and 320 nm, UVA between 320 and 400 nm and human visual between 400 nm and 780 nm.

Presently, light sources for general lighting purposes do not emit significant amounts of UV in order to realize controlled exposure to UVB. Only a limited number of special "full spectrum lamps" are available which produce UV radiation next to visible light. When installed to reach light intensities for use in general lighting applications (approx. between 100 and 1000 lux) only few of these lamps produce UV radiation in sufficient enough quantities to lead to a significant vitamin D synthesis. In that case however, considerable risk of developing erythema (reddening of the skin after UV exposure) exists because the relatively high UVA content relative to the UVB content produced by these lamps. Moreover, these lamps use a large number of phosphors with a wide emission spectrum so that the efficiency of these lamps - typically less than 50 lm/W - , which is nowadays considered to be too low for state of the art general lighting applications. WO2008/027438 describes a phosphor-based light therapy lamp for stimulating vitamin D production. This document proposes to control the output of the UVB radiation by diluting the UVB emitting phosphor with a non-UV emitting red or green phosphor. Such lamp is not suitable for general lighting purposes. Hence, there exists a need in the art for a UV-VIS light emitting system which stimulates the vitamin D synthesis and which is suitable for general lighting purposes.

SUMMARY OF THE INVENTION

It is an object of the invention to reduce or eliminate at least one of the drawbacks known in the prior art and to provide in a first aspect of the invention a UV-VIS light emitting system for stimulating vitamin D synthesis, comprising at least a first source emitting within the visible range and at least a second source emitting at least within the UVB range, wherein the light emitting system has a efficiency of 84 lm/W or larger and a spectral power distribution E(λ) such that the ratio Q between the dose rate for vitamin D

synthesis R_D = JE{λ)A_D{λ)dλ and the luminous flux Φ = JE{λ)v{λ)dλ is IQ^"6 J/m²lms or

larger.

The invention provides a UV-VIS light emitting system which is suitable for genera! lighting applications while providing controlled simulation of vitamin D synthesis, The use of such light source in general lighting applications provides people or animals which are too little or too short exposed to natural daylight the benefit of enhanced vitamin D synthesis.

In an embodiment the light emitting system, the first source comprises one or more visible light emitting phosphors and the second source comprises one or more UV emitting phosphors. The use of a phosphors allows easy implementation of the invention in luminescent discharge lamps designed for general lighting applications.

In one embodiment the first source comprises a mixture of visible light emitting phosphors, preferable a mixture of at least Europium doped Barium Magnesium Aluminate (BAM), Terbium doped Cerium Lanthanum Phosphate (LAP) and Europium doped Yttrium Oxide (YOX). In a further embodiment the mixture comprises 3-22 wt.% BAM, 31-47 wt.% LAP and 31-67 wt.% YOX. A mixture of BAM, LAP and YOX provides an efficient visible light emitting source for use in combination with UV emitting phosphors. In one embodiment the second source comprises at least one UV emitting phosphor selected from the group of: Strontium Aluminate: Ce (SAC), Lanthanum Phosphate:Ce (LAP:Ce), Gadolinium Lanthanum Borate:Bi (GLBB), Cerium Magnesium Aluminate:Ce (CAM) or Yttrium Phosphate:Ce (YPO). In a further embodiment the second source comprises at least 0.1 to 5 wt% of a phosphor selected from the group of SAC, LAP:Ce, GLBB, CAM or YPO. When mixing these UV phosphors with a suitable visible light emitting phosphor mixture a high efficiency UV-VIS phosphor blend is obtained.

In a further embodiment the UV phosphor is configured to emit UV light between 280 and 320 nm, preferably between 300 nm and 310 nm. Using a small bandwidth emissive UV phosphor will provide a relatively large vitamin D synthesis while minimizing at the same time undesirable effects of ertythema.

In yet a further embodiment the system further comprises a UVB transmissive (e.g. glass or quartz) envelope and/or a UVA filter. Using a UVA filter further suppression of ertyhema can be provided. In one embodiment the light emitting system is a discharge lamp comprising a

UVB transmissive discharge vessel, the discharge vessel enclosing, in a gastight manner, a discharge space provided with an inert gas and mercury and comprising discharge means for maintaining a discharge in the discharge space, at least a part the inner surface of the discharge vessel being provided with a luminescent layer comprising a mixture of at least BAM, LAP and YOX and at least one UVB emitting phosphor, preferably selected from the group: SAC, LAP:Ce, GLBB, CAM or YPO.

In one embodiment the system comprises at least a visible light emitting source and a UV emitting source. In another embodiment the visible light emitting source and/or the UV emitting source comprises a fluorescent discharge lamp, a high intensity discharge (HID) lamp or a LED lamp. Combining of one or more visible light emitting lamps with one or more UV emitting lamps provides a lamp assembly for general lighting purposes while at the same time allowing stimulation of vitamin D synthesis. In one embodiment a visible light luminescent discharge lamp may comprise at least BAM, LAP and YOX and the UV emitting discharge lamp comprising at least a UV emitting phosphor, preferably selected from the group: SAC, LAP:Ce, GLBB, CAM or YPO.

In a further aspect, the invention relates to a UV-VIS phosphor blend for use in a UV-VIS light emitting system as described above, wherein the blend comprises at least 3-22 wt.% BAM, 31-47 wt.% LAP, 31-67 wt.% YOX and at least 0.1 to 5 wt% of a UV phosphor, preferably selected from the group of SAC, LAP:Ce, GLBB, CAM or YPO.

Another embodiment of the invention is a UV-VIS light emitting system for stimulating vitamin D synthesis, comprising at least a first source emitting within the visible range and at least a second source emitting in the range of 300 - 320 nm, wherein the light emitting system has a spectral power distribution E(X) such that the ratio Q between the dose

rate for vitamin D synthesis R_D = E(λ)A_D(λ)dλ and the luminous flux Φ = E(λ)v(λ)dλ

is K)^"6 J/m²lm^'s or larger.

Yet another embodiment is a UV-VIS light emitting system for stimulating vitamin D synthesis, comprising at least a first source emitting within the visible range and at least a second source emitting in the range of 305 - 315 nm, wherein the light emitting system has a spectral power distribution E(X) such thai the ratio Q between the dose rate for

vitamin D synthesis R_D = JE{λ)A_D{λ}ϊk and the luminous flux Φ = J^*£(λ)κ(λ)ώλ is I Q^'6

J/m²lm^'s or larger. In a further embodiment further reduction of erythema may be achieved by blocking radiation with wavelengths smaller than 300 nm and larger than 320 nm using an appropriate filter, e.g. an interference filter, or combination of filters.

Thus, an embodiment of the invention is a UV-VIS light emitting system for stimulating vitamin D synthesis, comprising at least a first source emitting within the visible range and at least a second source emitting at least within the UVB range, wherein the light emitting system has a spectral power distribution E(X) such that the ratio Q between the dose

is 10^~6 J/m²lm^'s or larger, the system further comprising an optical filter or combination of filters that blocks radiation with wavelengths smaller than 300 nm or larger than 320 nm. Another embodiment of the invention is a UV-VIS light emitting system for stimulating vitamin D synthesis, comprising at least a first source emitting within the visible range and at least a second source emitting at least within the UVB range, wherein the light emitting system has a spectral power distribution F(λ) such that the ratio Q between the dose

is 10^~° J/m²lms or larger, the system further comprising an optical filter or combination of filters that blocks radiation with wavelengths smaller than 305 urn or larger than 315 run. When using a wavelength around 310 nm, the amount of erythema is much lower than for a wavelength around for example 290 nm. This means that the amount of UV radiation may be increased, while having a similar effective UV dose. In effect this means that the value of Q may be increased to greater than 10° J/m²lms or even greater than IG^"4

J/m²lms.

In one embodiment, the second source is a LED light source, because a LED light source has the advantage of providing narrowband UV emission such that the second source is emitting substantially within the 300 - 320 nm range, or even substantially within the 305 - 315 nm range. In this case, substantially means that at least 80%, but preferably at least 90% of the emitted UV power is within this range.

The invention will be further illustrated with reference to the attached drawings, which schematically will show embodiments according to the invention. It will be understood that the invention is not in any way restricted to these specific embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 depicts the action spectra for erythema and vitamin D synthesis. Fig. 2 represents a schematic drawing of a lamp according to one embodiment of the invention.

Fig. 3 represents a schematic drawing of a lamp according to another embodiment of the invention.

Fig. 4 depicts a curve showing the amount of vitamin D generation per erythemal damage.

DETAILED DESCRIPTION

The ability of radiation of a certain wavelength λ to induce a biological response is given by the relevant action spectrum. Fig.l (Bouillon et al., Action Spectrum for the production of previtamin D3 in human skin, CIE publication 174, 2006, ISBN 3901906509) shows that the action spectrum for erythema AE(λ)(solid line) and the action spectrum for vitamin D synthesis Ao(λ) (dashed line) are different. Vitamin D synthesis is mainly confined to the UVB part of the UV spectrum, whereas the erythemal action spectrum extends into the UVA band.

Given a spectral power distribution E(X) of a particular light source and the action spectrum for vitamin D synthesis the biologically effective dose rate for vitamin D

synthesis R_D = E(X)A_D(X)dX (in J/m² s) can be calculated. The spectral power distribution

can be measured using a spcctroradiomctcr, which measures for each wavelength, the rate at which energy is received, i.e. the power at that wavelength.

Evaluation of the relative "vitamin D synthesis promoting flux" O defined as the ratio between the dose rate for vitamin D synthesis R_D and the luminous flux,

Φ = E(X)v(X)dX (in lumen), i.e. the energy radiated over wavelengths sensitive to the

human eye, provides a way of determining whether a light source emits enough UVB for stimulating vitamin D synthesis when emitting visible light at an intensity which is suitable for general lighting applications.

The minimum effective dose required to produce an equivalent of an oral dose of about 1000 IU vitamin D for persons having a skin type I (the most sensitive skin type) is 37.2 Jm^"2. This dose D_D, which is simply the effective dose rate for vitamin D synthesis time the exposure time T_e in seconds, should be reached within a reasonable exposure time - 10 hours - using a light source producing a visible light intensity of around 1000 lux. Assuming that the spatial distribution of the UV radiation and the visible radiation emitted by a light source is similar, results in the condition that Q ≥ 1.10 ^ J/m²lm^'s.

A further condition relates to the efficiency of the light source. For fluorescent light sources the column efficiency is taken as the relevant source efficiency. The efficiency of fluorescent sources is primarily determined by the phosphor composition and a number of factors, which relate to the design of a particular fluorescent light source. To accommodate for these factors, for fluorescent lamps, the column efficiency, i.e. the efficiency of a particular phosphor determined when used in a straight T8 (25.4 mm diameter) 36W TL lamp, will be used as the relevant source efficiency. The following correction factors are used to calculate the column efficiency for a fluorescent source: wall losses (going from T12 to T8, from T8 to T5, from T5 to a compact fluorescent lamp (CFL)): -5% per step shielding losses (CFL): -15% losses due to an integrated driver (CFL-I): -15% outer bulb or cover for CFL: -5%

In all case the lamp power is reduced by 2 W due to electrode losses. So, a phosphor mix used in a straight T8 or T12 TL lamp with a column efficiency of 100 lm/W will give an efficiency of 94 lm/W in a 36 W TLD lamp and only an efficiency of 49 ml/W in a 10 W CFL-I lamp with an outer bulb. Nowadays, the column efficiency for fluorescent light sources for general lighting purposes should have values within the range of approximately 80 to 100 lm/W.

For general lighting purposes the light source further requires a colour- rendering index Ra of at least 70 or larger. The colour-rendering is a measure of the ability of a light source to reproduce the colour of various objects being lit by the source. It is based on the average of the colour rendering of the first eight colours from a set of fourteen reference colours, as described in "Method of Measuring and Specifying Colour Rendering Properties of Light Sources", CIE Publication No. 13.3, 1995, (SBN 3900734577).

Currently known broad spectrum light sources do not offer a vitamin D synthesis promoting flux of 10^"6 or larger in combination with a large column efficiency, Known broad spectrum lamps either have a relatively large column efficiency in combination with a small Q (~ 1Q^"'-1Q^~S) or a relatively large Q in combination with a low column efficiency (~ 40-60 lm/W). The applicant has found that UV/VIS light sources which are both suitable for vitamin D synthesis and general lighting purposes in fact can be realized.

A first embodiment of the invention relates to a fluorescent UV/VIS lamp with a glass envelope which is transparent for wavelengths of at least 300 nm and longer (e.g. a Philips type 290 soda-lime glass having a chemical composition of 73,lwt% SiO₂, 2,15wt% Al₂O₃, 16,8wt% Na₂O, 0,6 wt% K₂O, 7,lwt% MgO+CaO, <0,035wt% MnO, <0,15wt% Fe₂O₃, <0,15wt% SO₃ and < 0,025wt% TiO₂). The lamp comprises a mixture of visible light emitting phosphors and at least one of the UV emitting phosphors listed in Table 1 :

Here LAP: Ce refer to Lanthanum Phosphate: Ce, CAM refers to Cerium Magnesium Aluminate:Ce, SMS refers to Strontium Barium Magnesium Silicate:Pb, SAC refers to Strontium Aluminate:Ce and GLBB refers to Gadolinium Lanthanum Borate:Bi. In a further embodiment also Yttrium Phosphate: Ce (YPO) may be used.

The visible light emitting phosphor composition may be a mixture of Bao_.9Euo_.i MgAIi oO i₇ (Europium Barium Magnesium Aluminate or BAM), La₀.43Ceo.43Tbo.i4Pθ4 (Terbium Cerium Lanthanum Phosphate or LAP) and Y1.94Euo.06O3 (Europium activated Yttrium Oxide or YOX). The relative proportions in the mixture may range from 3-22 wt.% BAM, 31 -47 wt.% LAP and 31 -67 wt.% YOX, wherein the sum of the weight percentages equals 100%.

The composition listed in Table 1 are based on a visible light emitting phosphor mixture comprising 22 wt.% BAM, 47 wt.% LAP and 31 wt.% YOX. This mixture is blended (in wt.%) with one of the UV emitting phosphors LAP:Ce, CAM, SAC or GLBB. For each UVB emitting phosphor the relative vitamin D synthesis promoting flux Q and the efficiency is determined. The results indicate that the fluorescent light sources based on phosphor mixtures as listed in table 1 all satisfy the conditions that Q ≥ 1ΛO^~6 and that the efficiency is at least more than 85 lm/W. The colour rendering index of the light sources comprising the UV-VlS emitting phosphors as described in relation to table 1 is around 85. Particular advantageous results are obtained for compositions containing between 0.26 and 1.01 wt.% LAP:Ce, 0.12 wt.% SAC and 1.84 wt.% GLBB. For these compositions ratios of Q ranging between 4.010^"6 and 53 10° J/m²lm^'s and efficiencies ranging between 90 and 92 lra/W were obtained. Hence, the use of the mixture of the visible light phosphors and a UVB emitting phosphor in a fluorescent UV-VIS light emitting lamp as described above, results in a lamp having a sufficiently high efficiency, light intensity and colour rendering index for use in general lighting applications while at the same time facilitating the synthesis of a sufficient amount of vitamin D synthesis within a reasonable time.

In a further embodiment, the light source is configured to stimulate the synthesis of vitamin D within the maximum expected exposure time, e.g. 24 hours, at a light intensity of not more than 1000 lux, without causing significant erythema. For persons having skin type I the minimum dose to cause erythema is 200 Jm^"2. In practice however a factor 4 safety margin is incorporated providing a minimum dose of 50 Jm^"2. From the action spectra in Fig. 1, it follows that for wavelengths within a band of approximately 300 nm to 310 nm, the relative erythemal response is smaller than the relative vitamin D response. Hence, a small bandwidth emissive UV phosphor having its emission peak between 300 nm and 310 nm will provide a relatively large vitamin D synthesis while minimizing at the same time undesirable effects of ertyhema. The UV phosphors GLBB (emission peak at 312 nm) and LAP (emission peak at 315 nm) are particular suitable for this purpose. Further reduction of erythema may be achieved by blocking radiation with wavelengths smaller than 300 nm and larger than 320 nm using an appropriate filter, e.g. an interference filter, or combination of filters. Those skilled in the art will readily appreciate that the invention is not limited to the three-phosphor visible light emitting blends and the UV emitting phosphors as described in relation with table 1. Other suitable visible light emitting phosphors mixtures. In further embodiments LAP may be replaced by Cerium Magnesium Aluminate: Tb fine (CAT), Cerium Gadolinium Magnesium Borate: Tb fine (CBT), Barium Magnesium Aluminate:Eu,Mn or combinations thereof and BAM may be replaced by Strontium Chloro Apatite: Eu (SCAP). Additionally, Magnesium Fluor Germanate:Mn (MGM), Strontium Aluminate: Eu (SAE) and/or Ytrrium Aluminate: Ce (YAG) may be added to the phosphor mixtures described above in order to enhance the colour rendering index. UV phosphors having similar properties the phosphors described above may be used in order to achieve the desired effect.

Fig. 2 and Fig. 3 schematically show a cross-sectional view of a first and a second embodiment of a fluorescent UV-VIS light source according to the invention. Fig. 2 only shows one end portion of the light source 10 which comprises two mutually opposite, identical end portions, each sealing closing off one end of an elongated discharge vessel 12. The light sources 10,20 are low-pressure gas discharge lamps comprising a light-transmitting discharge vessel 12,22 which encloses a discharge space 14, 24 in a gas-tight manner. The discharge space 14,24 comprises a gas filling comprising mercury and a buffer gas, for example, argon or xenon. The low-pressure gas discharge lamp 10,20 further comprises discharge means 18,28 for maintaining a discharge in the discharge space 14,24. The discharge means 18,28 couple energy into the discharge space 14,24, for example, via capacitive coupling, inductive coupling, microwave coupling, or via electrodes.

In the embodiment of the gas-discharge lamp 10 shown in Fig. 2, the discharge means 18 comprise a set of electrodes 18. Only one electrode 18 of the set of electrodes 18 is shown in Fig. 2. The electrodes 18 are electrically connected through the discharge vessel 12 of the low-pressure gas discharge lamp 10. By applying an electrical potential difference between the two electrodes 18, a discharge is initiated between them. This discharge is generally located between the two electrodes 18 and is indicated in Fig. 1 as the discharge space 14. In the embodiment of the low-pressure gas discharge lamp 20 shown in Fig. 3, the discharge means 28 comprise an inductive coupler 28 for inductively maintaining the discharge in the low-pressure gas discharge lamp 20. Alternatively, the inductive coupler 28 may also be used for generating the discharge. The inductive coupler 28, also referred to as power coupler 28, generally comprises a coil wound on a ferrite core of, for example, Nickel- Zinc ferrite or Manganese-Zinc ferrite. The inductive coupler 28 is arranged in a protrusion 23 in the discharge vessel 22 and generates a varying electromagnetic field inside the discharge vessel 22 at the discharge space 24. The benefits of inductively generating and/or maintaining the discharge in the low-pressure gas discharge lamp 20 has the advantage is that the electrodes 18, which generally limit the lifetime of the low-pressure gas discharge lamps, can be dispensed with. Alternatively, the inductive coupler 28 may be arranged outside (not shown in Fig. 3) of the discharge vessel 22, resulting in a simplification of the manufacturing process for the discharge vessel 22.

Referring to Fig.2 and Fig.3 again, electrons and ions in the gas filling of the discharge space 14,24 are accelerated by the electromagnetic field and collide with the mercury compound in the gas filling. Due to the collision, the mercury atoms are excited and subsequently emit light, mainly ultraviolet light at a wavelength of approximately 254 nm. The low-pressure gas discharge lamp 10,20 comprises a luminescent layer 16,26 a mixture of phosphors as described above in relation with table 1. The luminescent layer absorbs and subsequently converts the absorbed ultraviolet light into visible and UVB light. In a further embodiment the UV-VIS light emitting system may comprise a combination of one or more visible light emitting lamps and one or more UV emitting lamps wherein the system is configured to have an efficiency of 84 lm/W or larger and spectral power distribution E(λ) such that the ratio Q is 10-6 J/m²lm^'s or larger. Various combinations of different types of visible and/or UV light emitting sources are be possible, e.g. fluorescent gas-discharge lamps similar to the ones described in relation with Fig. 2 and 3, high intensity discharge lamps (HID) comprising a gastight, light-transmissive discharge vessel of quartz glass containing an ionizable filling of rare gas and metal halides or a LED source. In one embodiment ionisable filling of a HID lamp may comprise an UV emitting iron-based salt such as FeI₃.

In a further aspect of the invention the amount of vitamin D generation is optimized with respect to the amount of erythemal damage. Division of the action spectrum for the vitamin D synthesis by the action spectrum for erythema as shown in Fig.l, results in a dashed curve as shown in Fig. 4. Said curve in Fig. 4 shows the amount of vitamin D generation per erythemal damage.

Although the maximum of the previtamin D3 formation lies at around 298 nm, the optimum excitation wavelength weighted by the Erythema action spectrum is found at 310 nm. Thus, when irradiating the skin at 310 nm wavelength, the highest amount of vitamin D is generated for the lowest UV dose. When compared to the spectrum emitted by the sun, calculations show that the gain in vitamin D can be up to 90% more for a given UV dose.

In a further embodiment further reduction of erythema may be achieved by blocking radiation with wavelengths smaller than 300 nm and larger than 320 nm using an appropriate filter, e.g. an interference filter, or combination of filters. When using a wavelength around 310 nm, the amount of erythema is much lower than for a wavelength around for example 290 nm. This means that the amount of UV radiation may be increased, while having a similar effective UV dose. In effect this means that the value of Q may be increased to greater than 10^~; J/m²lm^'s or even greater than 10^'4 J/m²lm^'s. In one embodiment, the second source is a LED light source, because a LED light source has the advantage of providing narrowband UV emission such that the second source is emitting substantially within the 300 - 320 nm range, or even substantially within the 305 - 315 nm range. In this case, substantially means that at least 80%, but preferably at least 90% of the emitted UV power is within this range. It is to be understood that any feature described in relation to any one embodiment may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims.

Claims

CLAIMS:

1. A UV-VIS light emitting system for stimulating vitamin D synthesis, comprising at least a first source emitting within the visible range and at least a second source emitting at least within the UVB range, wherein the light emitting system has a source efficiency of 84 lm/W or larger and a spectral power distribution E(X) such that the ratio Q

between the dose rate for vitamin D synthesis R_D = E(λ)A_D(λ)dλ and the luminous flux

Φ = JE{λ)v{λ)dλ is 10^"° J/m²lms or larger.

2. A light emitting system according to claim 1, wherein the first source comprises one or more visible light emitting phosphors and the second source comprises one or more UV emitting phosphors.

3. A light emitting system according to claims 1 or 2, wherein the first source comprises a mixture of visible light emitting phosphors, preferable a mixture of at least Europium activated Barium Magnesium Aluminate (BAM), Terbium activated Cerium Lanthanum Phosphate (LAP) and Europium activated Yttrium Oxide (YOX).

4. A light emitting system according to claim 3, wherein the mixture comprises 3-22 wt.% BAM, 31-47 wt.% LAP and 31-67 wt.% YOX.

5. A light emitting system according to any of claims 1 to 4, wherein the second source comprises at least one UV emitting phosphor selected from the group of: Strontium Aluminate:Ce (SAC), Lanthanum Phosphate:Ce (LAP:Ce), Gadolinium Lanthanum Borate:Bi (GLBB), Cerium Magnesium Aluminate:Ce (CAM) or Yttrium Phosphate:Ce (YPO).

6. A light emitting system according to claim 5, wherein second source comprises at least 0.1 to 5 wt% of a phosphor selected from the group of SAC, LAP:Ce, GLBB, CAM or YPO.

7. A light emitting system according to claims 1 to 3, wherein the UV phosphor is configured to emit UV light between 280 and 320 nm, preferably between 300 nm and 310 nm.

8. A light emitting system according to claim 1, wherein the system further comprises a UVB transmissive envelope and/or a UVA filter.

9. A light emitting system according to claim 1, wherein the light emitting system is a discharge lamp comprising a UVB transmissive discharge vessel, the discharge vessel enclosing, in a gastight manner, a discharge space provided with an inert gas and mercury and comprising discharge means for maintaining a discharge in the discharge space, at least a part the inner surface of the discharge vessel being provided with a luminescent layer comprising a mixture of at least BAM, LAP and YOX and at least one UVB emitting phosphor, preferably selected from the group: SAC, LAP:Ce, GLBB, CAM or YPO.

10. A light emitting system according to claim 1, wherein the system comprises at least a visible light emitting source and a UV emitting source.

11. A light emitting system according to claim 10, wherein visible light emitting source and/or the UV emitting source comprises a fluorescent discharge lamp, a high intensity discharge (HID) lamp or a LED lamp.

12. A light emitting system according to claim 10, comprising a visible light luminescent discharge lamp, preferably comprising at least BAM, LAP and YOX and a UV emitting discharge lamp comprising at least a UV emitting phosphor, preferably selected from the group: SAC, LAP:Ce, GLBB, CAM or YPO.

13. A UV7VIS phosphor blend for use in a UV-VIS light source according to claim 1, the blend comprising at least 3-22 wt.% BAM, 31-47 wt.% LAP, 31-67 wt.% YOX and at least 0.1 to 5 wt% of a UV phosphor, preferably selected from the group of SAC, LAP:Ce, GLBB, CAM or YPO.

14. A UV-VIS light emitting system for stimulating vitamin D synthesis, comprising at least a first source emitting within the visible range and at least a second source emitting at least within the UVB range, wherein the light emitting system has a spectral power distribution E(X) such thai the ratio Q between the dose rate for vitamin D synthesis

R_D = JE{λ)A_D{λ}Zk and the luminous flux Φ = J^*£(λ)κ(λ)ώλ is 10^'6 J/m²lms or larger,

the system further comprising an optical filter or combination of filters that blocks radiation with wavelengths smaller than 300 nr« or larger than 320 ntn.

15. A UV-VIS light emitting system according to claim 14, characterized in that the at least a second source emits substantially in the range of 305 - 315 nm and wherein the system is optionally free from filters.