Vitamin D lighting system

Abstract

A lighting system comprises a housing, an arrangement of UV-B LEDs in the housing and a fabric output screen which provides a UV-B exit surface. This provides UV-B light for an indoor application in order to replicate the health benefits of natural sunlight.

Claims

1. An indoor lighting panel for mounting on a wall or to a ceiling, wherein the indoor lighting panel comprises: a housing; an arrangement of UV-B LEDs in the housing; and a fabric output screen which provides a UV-B exit surface, wherein the fabric output screen is at least partially transparent to UV-B light, wherein the fabric output screen has a linear mass density of between 40 and 200 denier, wherein the fabric output screen is at least partially opaque to visible light, and wherein the fabric of the fabric output screen exhibits no fluorescence or phosphorescence upon absorption of UV-B light.

2. An indoor lighting panel as claimed in claim 1, wherein the housing comprises a base which carries the UV-B LEDs and a side wall around the base, wherein the side wall comprises a UV reflector.

3. An indoor lighting panel as claimed in claim 2, wherein the side wall comprises a polymer having embedded boron nitride particles.

4. An indoor lighting panel as claimed in claim 3, wherein the polymer comprises silicone or a fluoropolymer.

5. An indoor lighting panel as claimed in claim 1, wherein the fabric of the fabric output screen comprises ultra-high-molecular-weight polyethylene fibers.

6. An indoor lighting panel as claimed in claim 5, wherein the ultra-high-molecular-weight polyethylene fibers have a diameter in the range 2 mm to 5 mm.

7. An indoor lighting panel as claimed in claim 1, wherein the fabric output screen has an area of more than 1500 cm.sup.2.

8. An indoor lighting panel as claimed in claim 1, wherein the arrangement of UV-B LEDs comprises between 10 and 40 LEDs.

9. An indoor lighting panel as claimed in claim 8, wherein each UV-B LED has an output power in the range 400 μW to 800 μW.

10. A lighting installation comprising: one or more indoor lighting panels as claimed in claim 1; and one or more visible light luminaires.

11. A lighting installation as claimed in claim 10, comprising an office lighting installation.

12. A lighting installation as claimed in claim 11, wherein the indoor lighting panels each comprise a ceiling panel, and wherein the visible luminaires each comprise a ceiling panel.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Examples of the invention will now be described in detail with reference to the accompanying drawings, in which:

(2) FIG. 1 shows a UV-lighting system; and

(3) FIG. 2 shows an office space with a ceiling having visible lighting and UV-B lighting.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(4) The invention provides a lighting system, comprising a housing, an arrangement of UV-B LEDs in the housing and a fabric output screen which provides a UV-B exit surface. This provides UV-B light for an indoor application in order to replicate the health benefits of natural sunlight.

(5) FIG. 1 shows a UV-lighting system.

(6) The system comprises a carrier 10 on which an arrangement of UV-B LEDs 12 is provided. The carrier 10 for example comprises a printed circuit board (PCB), and the UV-B LED are surface mount packages for mounting on the PCB.

(7) A side wall 14 forms a housing together with the carrier 10 and the UV-B LEDs 12 provide UV light outwardly, normally away from the carrier 10. The housing may be any desired shape, such as rectangular, square or circular. The housing has a low profile so that it may be integrated into a ceiling structure for example. Alternatively, it may for a light fitting to be suspended below a ceiling.

(8) The housing is closed opposite the carrier 10 by a fabric sheet 16.

(9) The fabric sheet 16 can be produced at low cost, low weight and with large area. For example the overall system may have a size of around 45 cm×45 cm or 60 cm×60 cm. In this way it may form a panel of a modular lighting system. Generally, the size is more than 1500 cm.sub.2, for example more than 2000 cm.sup.2 for example more than 3000 cm.sup.2.

(10) In a preferred example, the fabric sheet comprises fibers of ultra-high-molecular-weight polyethylene (known as UHMWPE or UHMW). This material is a type of thermoplastic polyethylene with extremely long chains, with a molecular mass usually between 3.5 and 7.5 million atomic mass units. The longer chain serves to transfer load more effectively to the polymer backbone by strengthening intermolecular interactions. This results in a very tough material.

(11) UHMWPE fibers are for example commercially available from the chemical company DSM (trade mark), under the trade name Dyneema (trade mark). When formed into fibers, the polymer chains for example attain a parallel orientation greater than 95% and a level of crystallinity from 39% to 75%.

(12) It is known that UHMWPE is very resistant to UV radiation (as well as to water, moisture, most chemicals and micro-organisms).

(13) The use of UHMWPE fibers in this application is based on the recognition that the fibers are highly (compared to other fibers) transparent to UV light.

(14) The fibers for example have a diameter in the range 2 mm to 5 mm for example a twine diameter of 3.3 mm and weight of in the range 2 to 10 g/m. The fabric is woven in such way as to provide a minimum linear mass density for example of 40 to 200 denier.

(15) The fabric is then opaque or translucent to light in the visible light spectrum so that the LEDs 12 and other components are not visible to the human eye.

(16) By way of example, the fibers have an axial refractive index of 1.59 and a transverse refractive index of 1.53, hence a birefringence of 0.06. They are also highly transparent to infrared, near infrared and radar.

(17) The resulting fabric is for example at least 80% transmissive to UV light, preferably at least 90% transmissive and preferably at least 98% transmissive.

(18) The resulting structure is also opaque (or translucent) to visible light so that the visual appearance of the UV-B LED array is masked. The screen may have a desired visual color and/or pattern, selected for consistency with the decor of the indoor space in which the system is to be used.

(19) The side wall 14 is formed or a boron nitride powder filled polymer. The polymer is for example a silicone or fluoropolymer.

(20) This provides a structure which is highly reflective to UV-B light. For example, a reflection may be achieved of 95% or higher.

(21) The UV-B LEDs are designed to provide a dose of UV-B light which is sufficient to provide the advantages of vitamin D production, but not sufficient to cause skin damage. By way of example, the light intensity of the system as a whole is based on each UV-B LED having an output power of 400 μW to 800 μW. The total number of UV-B LEDs can be for example in the range 10 to 40 in the panel, giving a total output power in the range 4 mW to 30 mW.

(22) UV-B LEDs are commercially available, and are mainly used in medical applications, for example for medical photometry. There are also commercially available UV-B lighting products for stimulating plant growth for illuminating terrariums. The UV-B wavelength is in the range 280 nm to 315 nm.

(23) FIG. 2 shows an office space 20 with a ceiling 22 having visible lighting panels 24 (luminaries) and UV-B lighting panels 26 each of the type as described above. In combination, the panels provide the visual lighting required as well as a desired level of UV-B radiation.

(24) The system may be used as part of an office lighting system, but it may also be used for other indoor lighting applications.

(25) The example above makes use of a panel which is dedicated to the generation of UV-B radiation. It is also possible to combine UV-B radiation and visible lighting in the same panel. In such a case, a visually transparent (but typically diffusive) fabric is required so that both UV and visible light can escape from the panel. A diffusive fabric will again mask the appearance of the LED structure beneath.

(26) Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.