WO2007035907A2

WO2007035907A2 - Germicidal lamp

Info

Publication number: WO2007035907A2
Application number: PCT/US2006/036945
Authority: WO
Inventors: Eugene I Gordon
Original assignee: Germgard Lighting Corporation
Priority date: 2005-09-21
Filing date: 2006-09-21
Publication date: 2007-03-29
Also published as: WO2007035907A3

Abstract

The present invention provides a light source having germicidal properties. The light source includes a radiation source capable of producing radiation at a wavelength that can deactivate pathogens. A housing contains the radiation source and includes a visible light transmitting component that is coated with a phosphor capable of producing visible light when excited. The housing includes multiple openings that allow air to flow through the interior of the light source where it is exposed to the germicidal radiation. The radiation source can include an enclosure having a quartz-L component capable of absorbing radiation having a wavelength of 185 nm, which can create ozone. Additionally, the light source can include a blower that increases the airflow through the light source. The light source can be tubular to approximate a traditional fluorescent light, or it can include a threaded base so that it can be coupled to an incandescent light fixture.

Description

GERMICIDAL LAMP

This application claims priority pursuant to 35 U. S. C. § 119 from Provisional

Patent Application Serial No. 60/719,531 entitled "Germicidal lamp," filed September 21, 2005, the entire disclosure of which is hereby incorporated by reference.

FIELD OF THE INVENTION This invention relates to a visible light source having germicidal properties, and more particularly to a visible light source that deactivates airborne pathogens contained in air flowing through the interior of the light source.

BACKGROUND OF THE INVENTION Ultra-violet germicidal irradiation (UVGI) can be use to deactivate pathogens such as anthrax, smallpox, viral hemorrhagic fevers, pneumonic plague, glanders, tularemia and drug resistant tuberculosis. Pathogens that have a relatively thick cell wall, such as spores, are more resistant to UVGI because the cell wall is not easily penetrated. However, with greater intensity and longer exposure times, even the more resistant pathogens are deactivated by UVGI.

A germicidal lamp 100 (Figure 1) producing UVGI 130 can be used in a variety of spaces and locations to maintain a low effective pathogen count in the air, and to disinfect critical surfaces. For example restaurants, factories, planes, trains, ships, cars and mail processing facilities can employ germicidal lamps to increase protection against many types of dangerous bacteria, viruses and spores. Germicidal lamps 100 can also be used in water treatment systems and swimming pools to purify water by killing pathogens and neutralizing toxic substances. Medical facilities, such as operating rooms, isolation areas, patients' rooms, other nursing care facilities, can use germicidal lamps 100 to maintain a low effective pathogen count in the air, and to disinfect critical surfaces and equipment. Furthermore, germicidal lamps 100 can be used for product protection in various locations, such as walk-in refrigerators and meat holding rooms, bakeries, wineries, dairies, bottling plants, and the pharmaceutical industry.

The effectiveness of UVGI derives from a band of UV-C radiation centered at a wavelength of 265 nm plus or minus 30 nm. The UV-C radiation affects the DNA and eliminates the ability of a pathogen to reproduce. Pathogens that can't reproduce are not infectious, and are therefore harmless. Germicidal reduction of the density of reproducing pathogens in air is based on the ability of UV-C radiation, in a narrow wavelength band from a spectral line centered at λ253.7 nm, to eliminate the ability to reproduce of a percentage of pathogens of a given type in the air surrounding the tube.

Radiation intensity is a measure of radiant power incident per unit area. If a pathogen is in the presence of germicidal radiation for a given exposure time, the integral of the radiation intensity experienced by the pathogen over time determines the radiant exposure per unit area. The surface area of the pathogen defines the actual energy incident on the pathogen. Most of the incident energy is absorbed, which results in the deactivation of the pathogen. Deactivation is also referred to as inactivation. Typical radiation intensity at the germicidal lamp surface is about 500 watts/m . At the external surface of a typical tubular lamp with a 2-cm diameter, an exposure of « 100 J/m² is delivered in 0.2 second. The radiation intensity at a radius,

R, has an R^"1 dependence when R is much less than the tube length. The intensity of the radiation falls off at a rate proportional to R^"2 at distances much greater than the tube length. Hence, for a given exposure the required exposure time increases somewhere between linearly and quadratically as the distance from the tube increases.

At a distance of 2 meters from the tube the exposure time to achieve an exposure of

100 J/m² is increased approximately 10,000 times relative to the value at the tube surface to about 2000 seconds (« ¹A hour).

A study by P.W. Brickner et al. discusses the duration and intensity of exposure required to deactivate various pathogens. See P.W. Brickner, R.L. Vincent, M. First, E.A. Nardell, M. Murray, and W. Kaufman, "The Application of Ultraviolet Germicidal Radiation to Control Transmission of Airborne Diseases: Bioterrorism Countermeasure," PUBLIC HEALTH REPORTS, Vol. 118, pp. 990-114, March- April 2003 {available at http://www.publichealthreports.Org/userfiles/l 18_2/118099.pdf) (hereinafter, "the Brickner study").

The following table includes a sample of the data presented in the Brickner study. The table describes the average flux used in the experiment not the actual absorbed energy or dose. Differences reflect both different size of the pathogen and different required dose.

Examples of actinic exposure data for 90% reduction in colony formation

Microorganism Required Radiant Exposure for Type

However, exposing humans and animals to germicidal lamp radiation can result in irritation of the skin and mucous membranes, and potentially result in even more harmful effects. Germicidal lamps also generate radiation in a spectral line at λl85 nm. This wayelength of radiation can produce abundant amounts of ozone in the surrounding air. Ozone is an extremely active oxidizer, and quickly destroys microorganisms on contact. Ozone also acts as a deodorizer and air purifier. However, increased levels of ozone are not desirable and can be harmful or irritating to people in the proximity of the increased ozone levels. Additionally, the cornea can be irritated by long exposure to the UV-C radiation produced by a conventional germicidal lamp. There are strict limits on the allowable ozone exposure defined in the U.S. by OSHA and corresponding bodies worldwide.

Thus, germicidal lamps are typically installed in spaces that are sufficiently removed from populated areas so as to avoid the negative effects of UV-C and increased ozone production. Furthermore, the installation typically requires specialized hardware fixtures to provide the necessary housing and electrical power. The present invention provides improved flexibility and versatility of the application of germicidal radiation, and addresses some of the potentially harmful or irritating by-products of germicidal lamps.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, a light source having germicidal properties is presented. The light source includes a radiation source capable of producing at least one wavelength having germicidal properties. The radiation source is contained inside a housing that includes at least one visible light transmitting component having an inner surface, an outer surface, and openings that allow air to pass through the housing so that the air is exposed to the germicidal radiation. The inside surface of the visible light transmitting component of the housing is coated with a phosphor that produces visible light when excited by the radiation produced by the radiation source and is positioned with respect to the radiation source such that the phosphor is excited by the radiation emitted by the radiation source.

In accordance with a further aspect of the present invention, the radiation source produces radiation having a wavelength of about 185 run and produces radiation having a wavelength of about 253.7 nm. Furthermore, the housing of the radiation source can include a quartz-L component which absorbs the 185 nm wavelength radiation, thereby reducing the amount of ozone generated by the radiation source. Additionally, the light source can include a blower unit that can increase the airflow through the housing of the light source, thereby increasing the volume of air per unit time that is exposed to the germicidal radiation. In yet a further aspect of the present invention, the light source can approximate the size and shape of a conventional fluorescent light bulb so that it can be substituted for a conventional fluorescent light in fluorescent lighting fixtures. Alternatively, the light source can include a threaded base having electrical contacts that are configured such that the light source can be inserted into and powered by a conventional incandescent light socket.

These and other aspects, features and advantages will be apparent from the following description of certain embodiments and the accompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features of the present invention will be more readily apparent from the following detailed description and drawings of the illustrative embodiments of the invention wherein like reference numbers refer to similar elements throughout the views and in which:

Figure 1 illustrates a conventional germicidal lamp;

Figure 2 illustrates a light source having germicidal properties in accordance with one embodiment of the present invention;

Figure 3 illustrates a cross section of the embodiment depicted in Figure 4;

Figure 4 illustrates a light source having germicidal properties and increased air flow in accordance with a further embodiment of the present invention; and

Figure 5 illustrates a light source having germicidal properties that approximates the geometry of an incandescent light bulb in accordance with yet a further embodiment of the present invention. DETAILED DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS

By way of overview and introduction, the present invention comprises a light source that can be used to illuminate an area and sterilize the air by deactivating pathogens using germicidal radiation. The light source can be used in a conventional incandescent or fluorescent light fixture and thus does not require unique hardware or installation procedures. The light source includes a germicidal radiation source that is contained in an exterior housing. The housing includes openings that allow air to pass through the volume created between the exterior of the germicidal bulb and the interior of the housing, where it is exposed to germicidal radiation and the pathogen density in the air is reduced. Additionally, the housing includes a visible light transmitting component, e.g. glass, that is coated on the interior surface with a phosphor that produces visible light when excited by the same germicidal radiation. Thus, the radiation that deactivates pathogens in the air flowing through the interior volume of the housing also excites the phosphor coating the housing thereby generating light, preferably in the visible spectrum, which passes through the light transmitting component virtually without loss and illuminates the surrounding space.

With reference to Figure 2, the light source 200 includes a germicidal lamp 100 contained within a housing 210. At least a portion of the housing 210 transmits visible light, e.g. glass. The germicidal lamp 100 acts as a source of radiation 130 having germicidal properties. The space between the germicidal lamp 100 and the housing 210 ("the sterilizing volume 240") is filled with UV-C radiation 130. Thus, any air within the sterilizing volume 240 between the outer surface of the surface of the germicidal lamp 100, and the inner surface of the housing 210, is exposed to the germicidal radiation 130 produced by the germicidal lamp 100. The light source further includes openings 230 that permit air to flow through the sterilizing volume 240.

A phosphor 220 coats the inner surface of at least the glass portion of the housing 210. When the phosphor is illuminated by the radiation emitted by the germicidal lamp, the phosphor is excited and emits visible light 250. The emitted light 250 preferably includes wavelengths similar to a conventional fluorescent or incandescent light. The UV-C radiation produced by the germicidal lamp is absorbed by the phosphor 220 and the glass housing 210. Therefore, the UV-C radiation is contained within the sterilizing volume 240 and will not escape the housing 210. The UV-C radiation is preferably produced by a germicidal lamp 100 having a quartz discharge tube that contains a gaseous mixture 140 inside the lamp 100 comprising mercury vapor and a noble gas, preferably argon, at reduced pressure. The discharge produced by the lamp 100 contains excited and ionized argon atoms and free energetic electrons. However, some argon atoms are excited to a long-lived metastable state. Argon atoms in this state transfer their excitation energy and ionize a mercury atom by collision. The mercury ion in a highly energetic state recombines with an electron and the resulting excited mercury atom produces the short wavelength UV-C radiation. The gas discharge mechanism is similar to the mechanism for producing phosphor exciting radiation within conventional fluorescent tubes.

Preferably, a ballasted, AC voltage (e.g., 120 volts) is applied across the electrodes 120. A gas discharge is initiated and the ballast controls the current. For the particular gases referenced above, the predominant wavelength of the radiation is 253.7 nm. The germicidal lamp enclosure 110 is preferably substantially transparent to radiation having a wavelength of 253.7 nm. One substance that is suitable for this application and is transparent to the 253.7 nm wavelength is quartz. Thus, a germicidal lamp enclosure 110 composed of quartz would pass the 253.7 nm wavelength radiation into the sterilizing volume 240 and deactivate the pathogens contained therein. Alternatively, other sources of UV-C radiation can be utilized in the geπnicidal light source 200. For example, the light source 200 can utilize an LED (not shown) that produces UV-C radiation in the same band as conventional germicidal lamps. Such an LED would produce similar deactivating germicidal radiation 130 that would be converted to visible light 250 by the phosphor 220 coating the housing 210.

However, as discussed above, germicidal lamps also typically produce radiation having a wavelength of 185 nm, which, if oxygen is present in the gas surrounding the envelop, can result in increased ozone production. Thus, the material used to construct the germicidal lamp enclosure 110 is preferably chosen to be transparent to 253.7 nm wavelength radiation, but opaque to 185 nm wavelength radiation. Certain types of quartz satisfy these requirements. One possible material is quartz-L. The letter "L" is used to indicate the type of quartz and the level of ozone produced by a germicidal lamp composed of the material. The letter "L" indicates production of a negligible amount of ozone. Thus, little or no UV-C radiation is transmitted into the area surrounding the light source, and the amount of ozone produced is inconsequential or non-existent.

Alternatively, a customized or controlled level of ozone can be created within the sterilizing volume 240 to increase the sterilizing effects of the germicidal light. For example, the lamp enclosure 110 can include "VH" quartz, which is used in very high ozone producing lamps. Thus, a combination of quartz- VH and quartz-L, for example spliced together, can produce variable levels of ozone production to oxidize pathogens in the sterilizing volume 240. Furthermore, a filter (not shown) can be included at the openings 230 of the housing to deactivate any ozone produced before it escapes the sterilizing volume 240. The filter is preferably a catalyst, such as activated carbon, to increase the rate of ozone decay to oxygen.

Figure 3 illustrates a cross-section of the light source 200 having germicidal properties that is illustrated in Figure 2. In this embodiment, the germicidal lamp 100 is cylindrical and is surrounded by a cylindrical housing 210. The argon-mercury vapor is contained within the inner volume 140 defined by the quartz enclosure 110. Preferably, the enclosure 110 is composed of a substance that absorbs 185 nm wavelength radiation. However, the germicidal 253.7 nm wavelength radiation produced by the germicidal lamp 100 passes through the quartz enclosure 110 wall and into the sterilizing volume 240. Any air passing through the sterilizing volume 240 is exposed to the germicidal radiation, thereby deactivating the pathogens contained therein. The level of pathogen deactivation varies depending on the type of pathogen, the intensity of the radiation, the duration of the exposure (i.e. how quickly the air passes through the sterilizing volume 240).

The radiation emitted by the germicidal lamp excites the phosphor 220 that coats the inner wall of the housing 210. As the phosphor 220 relaxes from the excited state, the phosphor 220 emits light, preferably in the visible spectrum. The housing 210 is preferably glass or some other substance known in the art that will allow the visible light to pass relatively losslessly through the housing, thereby illuminating the area surrounding the germicidal light source.

While the duration of exposure to UV-C radiation is one of the factors determining the level of pathogen deactivation, the intensity of the UV-C radiation within the sterilizing volume can be sufficiently high so as to require only short exposures to produce virtually complete deactivation of the pathogens in the air passing through. Thus, the displacement of air through the sterilizing volume 240 may be increased to take advantage of the short exposure time that is required for sufficient deactivation.

Figure 4 illustrates a light source 400 having germicidal properties that includes an axial flow fan 410 coupled to housing opening 430. Any form of blower can be used to push or pull air through the sterilizing volume 240. Furthermore, the blower is not required to be coupled to the opening, but can be positioned in various locations that effectively increase air flow through the sterilizing volume 240, including within the housing 210, the electrical contact cap 420, or in the ballast 560 (Figure 5). Air flow can further be increased by including multiple openings in the housing or multiple blowers.

Convection can also be used to increase air flow through the sterilizing volume 240. However, convection will be affected by the orientation of the light source as well as the position of the openings 230 in the housing 210. A heating element (not shown) can be included in the light source and positioned to further increase the convective currents through the light source, thereby increasing the volume of air exposed to the germicidal radiation. The geometry of the light source 400, including the housing 210 and the germicidal lamp 100, can be chosen so as to approximate the dimensions (i.e., length and diameter) and electrical contacts 120 of a conventional fluorescent light. As illustrated in Figures 2-4 the outer diameter and length of the structure can be the same as that of a conventional fluorescent tube. Thus, it could readily replace conventional fluorescent tubes in the same fixture. The germicidal lamp 100 contained within the housing 210 can have a smaller diameter. Voltage limitations can be accommodated by operating multiple shorter germicidal lamps 100 mounted coaxially within the housing 210 and powering the lamps 100 in parallel at normal voltage.

Additionally, non-conventional geometries can be created by including one or more germicidal lamps 100 in a non-conventional housing. For example, a rectangular housing (not shown) having a phosphor 220 coated surface and containing several germicidal lamps 100 can provide the same sterilizing and illuminating effects as the conventional tubular geometry described above.

With reference to Figure 5, the light source 500 having germicidal properties can also be configured to approximate a conventional incandescent light bulb with a threaded base 550. One possible configuration imitating an incandescent bulb incorporates a convoluted germicidal lamp 570 mounted inside a translucent glass bulbous housing 510 having a base 560 containing the additional electronics (e.g., ballast and starter) needed to operate the germicidal lamp 570. The space between the germicidal lamp 570 and the bulbous housing 510 acts as the inactivation volume 540. The housing 510 can be bulb shaped (as shown) or alternatively shaped to accommodate a variety of light fixtures. The phosphor 520 coats the inside of the housing 510 and is impinged by the radiation emitted by the germicidal lamp 570, as described above with respect to the tubular geometries. Openings 530 in the housing 510 can be located, for example, at the top of the bulbous housing 540 and within the base 560 of the housing 510. This configuration of openings will increase convective flow through the sterilizing volume 540. Additionally, a blower unit, such as an axial flow fan, can be included in the base 560 to further increase the air flow through the sterilizing volume 540. A germicidal light source having this configuration and geometry can replace incandescent bulbs in conventional screw-in base lighting fixtures, thus providing higher efficiency and longer life as well, similar to compact fluorescent lamps, while simultaneously sterilizing the air flowing through the sterilizing volume 540. It could also replace conventional compact fluorescent lamps having a screw in base.

Light sources having germicidal properties can be used in virtually any environment that uses a conventional fluorescent, compact fluorescent or incandescent light bulb. The germicidal light source can provide a means to protect occupants of closed structures (buildings, offices, conference rooms, hotels, schools, dormitory rooms, assembly areas, meeting halls, public or private waiting rooms, sports facilities, indoor shopping malls, restaurants, hospitals, surgical suites, doctors offices, transportation vehicles and depots, etc.) against accidental exposure resulting from infected individuals who might introduce pathogenic aerosols into the environment by coughing, sneezing or touching. Thus, it may be used to protect occupants in such spaces from infection arising from other individuals entering or occupying the same • space. It will also protect against the intentional release of aerosolized bioterror agents (bacteria, viruses, fungi, molds) into such spaces.

While the invention has been described in connection with a certain embodiment thereof, the invention is not limited to the described embodiments but rather is more broadly defined by the recitations in the claims below and equivalents thereof.

Claims

I claim:

1. A light source having germicidal properties comprising: a radiation source capable of producing at least one wavelength having germicidal properties; a housing containing the radiation source, the housing including a visible light transmitting component having an inner surface and an outer surface, and a plurality of openings allowing air to pass through the housing; and a phosphor that produces visible light when excited by radiation produced by the radiation source, the phosphor coating the inner surface of the visible light transmitting component, wherein the inner surface of the visible light transmitting component is positioned with respect to the radiation source such that the phosphor is excited by the radiation emitted by the radiation source.

2. The light source of claim 1, wherein the radiation source produces radiation having a wavelength of about 185 nm and a wavelength of about 253.7 nm.

3. The light source of claim 2, wherein the radiation source includes an enclosure having a quartz component capable of at least partially absorbing 185 nm wavelength radiation whereby the level of ozone produced by the light source is reduced.

4. The light source of claim 1, wherein the phosphor emits light in a visible spectrum when excited by the radiation emitted by the radiation source.

5. The light source of claim 1, wherein the radiation source includes a discharge volume containing argon gas at low pressure and also containing a vapor of mercury atoms.

6. The light source of claim 1, further comprising a blower unit configured to increase air flow through the housing.

7. The light source of claim 6, wherein the blower unit includes an axial flow fan coupled to one of the plurality of openings of the housing.

8. The light source of claim 1, wherein the germicidal radiation source includes a gas discharge tube.

9. The light source of claim 8, wherein the housing includes a tubular structure having a diameter and a length, the housing diameter being greater than a diameter of the radiation source and the housing length being substantially equal to a length of the radiation source, so as to approximate the shape of a conventional fluorescent light source.

10. The light source of claim 1, wherein the housing further includes a threaded base containing electrical contacts configured to be coupled to at least one of an incandescent lighting socket and a compact fluorescent lighting socket.

11. The light source of claim 1, further comprising a plurality of radiation sources having germicidal properties.

12. The light source of claim 11 , wherein at least two of the plurality of radiation sources are operated in parallel.

13. The light source of claim 1, further comprising a heat source to increase convective currents through the housing.

14. The light source of claim 1, wherein the radiation source includes an enclosure having a quartz component capable of at least partially transmitting 185 run wavelength radiation, whereby the level of ozone produced by the light source is increased.

15. The light source of claim 14, further comprising a catalyst to increase the rate of decay of ozone.

16. The light source of claim 15, wherein the catalyst includes activated carbon.