US20220205656A1

US20220205656A1 - Ultraviolet light system for use in heating, ventilation, and air-conditioning systems

Info

Publication number: US20220205656A1
Application number: US17/646,169
Authority: US
Inventors: Michael Milton
Original assignee: Individual
Current assignee: Individual
Priority date: 2020-12-28
Filing date: 2021-12-28
Publication date: 2022-06-30

Abstract

An ultraviolet light-emitting device can be used to inactivate pathogens in air circulating through an HVAC system. The UV device can include a first and optionally a second UV light source that emits UV light at a predetermined peak wavelength that is selected to inactivate a specific pathogen. The second UV light source can emit a different predetermined peak wavelength that is selected to inactivate a different pathogen. The UV light sources can be included in a housing located within the HVAC system. Two or more housings can be placed within the same or different components of the HVAC system. The two or more housings can include UV light sources that emit the same or different peak wavelengths. An amplifier can be used to increase the intensity of the UV light emitted such that a desired percentage of a specific pathogen is inactivated.

Description

TECHNICAL FIELD

Ultraviolet (UV) light can be used to kill viruses or bacteria. A UV light system can be used in an air system of a residential building, commercial building, automobile, or airplane.

BRIEF DESCRIPTION OF THE FIGURES

The features and advantages of the embodiments will be more readily appreciated when considered in conjunction with the accompanying figures. The figures are not to be construed as limiting any of the embodiments.

FIG. 1 is a schematic illustration of an HVAC system with a UV light-emitting device according to certain embodiments.

FIG. 2 is a cross-sectional view of a UV light-emitting device according to certain embodiments.

FIG. 3 is a cross-sectional view of a UV light-emitting device according to certain other embodiments.

DETAILED DESCRIPTION

Ultraviolet (“UV”) light, which is a form of electromagnetic radiation, can be used to inactivate microbial contaminants and viruses (collectively referred to as “pathogens”) in a variety of applications and industries. UV lights used for this purpose are commonly referred to as germicidal UV lights (“GUV” lights). For example, UV light can be used in water treatment facilities, food processing facilities, swimming pools, hot tubs, surfaces, and ducts for heating, ventilation, and air conditioning (“HVAC”) systems. A variety of lamps can be used to emit UV light including, but not limited to, low-pressure, mercury-vapor lamps and light-emitting diode (“LED”) lamps.
The wavelength from UV light is in the range of 10 to 400 nanometers (nm) and has a shorter wavelength than visible light, but a longer wavelength than X-ray radiation. UV light emitted at certain wavelengths can inactivate a pathogen by damaging the pathogen's DNA/RNA so that it cannot reproduce; therefore, rendering it harmless, even though the pathogen may not be killed. Pathogens vary in their sensitivity to specific UV wavelengths. For example, ultraviolet-A (UV-A) light at a 365 nm wavelength has been shown to have antimicrobial activity against pathogens such as Escherichia coli and Candida albicans. By way of another example, some studies have shown that SARS-CoV-2, commonly referred to as COVID-19, has a susceptibility to ultraviolet-C (UV-C) wavelengths in the range of 267-297 nm for surface treatment and 222 nm for air treatment.
UV-A, UV-B, and UV-C are all forms of UV light, with UV-C having the shortest wavelength (100-280 nm), UV-B having the second shortest wavelength (280-315 nm), and UV-A having the longest wavelength (315-400 nm) of the three forms. UV-C, having the shortest wavelength, has been shown to be the most effective against certain pathogens and can be thought of as being stronger than UV-A. UV-C from sunlight is absorbed by the Earth's ozone layer and does not penetrate through the atmosphere. Accordingly, all UV-C light is artificially produced via UV lamps.
Energy density (commonly referred to as the UV dose) and irradiance (commonly referred to as the UV intensity) are two key parameters that can help characterize the performance of a UV light source. Irradiance can be defined as the instantaneous number of photons at a specific wavelength or range of wavelengths striking a surface per unit area and is generally expressed in units of watts per square centimeter (W/cm²). Energy density is the time-integral of irradiance and represents the total sum of photons of a specific wavelength or wavelength range received by a specific area of the surface within a specific length of time and is generally expressed in units of joules per square meter (J/m²). Accordingly, both the UV dose and the intensity play a crucial role for sanitizing surfaces or air.
D90 values indicate the necessary radiant exposure of an ultraviolet dose to inactivate 90% of a particular pathogen. Below is a partial reproduction of a table reporting D90 values from various studies performed on Coronaviruses under UV light exposure.


Microbe	D90 Dose (J/m²)

Coronavirus	6.6
SARS-CoV-2 (Italy-INMI1)	12.3
SARS Coronavirus (Frankfurt 1)	16.4
SARS-CoV-2 (SARS-CoV-2/Hu/DP/Kng/19-027)	41.7

To inactivate a sufficient percentage of a pathogen for sanitation and/or sterilization purposes, not only must the correct wavelength be emitted, but also the UV dose must meet or exceed the minimum required dose. The UV dose can be increased by adjusting the intensity of the UV light output, the exposure time of the pathogen to the UV light, or a combination of both.
Current UV light systems for HVAC systems have several disadvantages. One significant disadvantage is the inability to attain the requisite UV dose to protect people against exposure to a pathogen from recirculated air through the HVAC system. Another disadvantage is that the UV lamp may emit a wavelength that inactivates one pathogen but does not inactivate other pathogens. This inability to emit a range of wavelengths or different wavelengths can result in protection existing for fewer pathogens than is needed. Thus, there is a critical need—especially for inactivating a plurality of different bacteria and viruses—for improved UV systems that can be used in HVAC systems.
It has been discovered that an ultraviolet light-emitting device for use in a heating, ventilation, and air conditioning system can be used to inactivate a variety of bacteria and viruses. The novel device can include one or more UV light sources that emit UV-A, UV-B, UV-C, or combinations thereof in a variety of wavelengths or wavelength ranges. The novel device can also include features and/or components that increase the UV dose via amplification of the light intensity or exposure time. By increasing the UV dose, a greater number or percentage of pathogens can be inactivated compared to traditional UV systems.
According to any of the embodiments, an ultraviolet light-emitting device for use in a heating, ventilation, and air conditioning system, the device can include: a first housing located within a component of the heating, ventilation, and air conditioning system, wherein at least a portion of the housing is transparent; a first ultraviolet light source located within the housing and adjacent to the portion of the transparent housing, wherein the ultraviolet light source emits ultraviolet light at a pre-selected peak wavelength; and a power source for supplying power to the first ultraviolet light source.
Turning to the figures, FIG. 1 is a schematic illustration of a heating, ventilation, and air conditioning (“HVAC”) system 100. As used herein, the phrase “HVAC system” means any system that is designed to heat and cool an interior space. As can be seen in FIG. 1, the HVAC system 100 can include any or all of the following components that are common for heating and cooling a building: one or more return air ducts 121; a return plenum 122; a furnace 123; an evaporator coil 124; a supply plenum 125; a transformer/power supply 126; and one or more supply air ducts 127. The HVAC system 100 can include other components not shown in the drawings depending on the interior space the HVAC system is designed to heat and cool. By way of example, the components of an HVAC system for use in a vehicle can include an A/C compressor, a condenser, a radiator fan, a blower fan, an evaporator, tubing, and a refrigerant among other components. It is to be understood that the UV light-emitting device can be used in any system designed to heat and cool an interior space including, but not limited to, a house, office building, workshop, motor vehicle, temporary shelter, warehouse, and manufacturing facility.
The HVAC system 100 includes a UV light-emitting device 110. As shown in FIG. 2, the UV light-emitting device 110 can include a housing 111. The housing 111 can be a variety of shapes and sizes. For example, as shown in FIG. 2, the housing 111 can have a conical shape. As shown in FIG. 3, the housing 111 can have a cylindrical shape. The housing 111 can also be cubic, rectangular, or other shapes. A portion of the housing 111, for example as shown in FIG. 2, can be opaque. An opaque portion of the housing can be made from a variety of materials. Non-limiting examples of opaque materials include metals, metal alloys, and hardened plastics.
The dimensions of the housing 111 can be selected based on a variety of factors. Such factors can include, without limitation, the ability to house the dimensions and desired number of the UV light source(s) 112 contained within the housing, the dimensions of the component of the HVAC system 100 in which the housing is to be placed, the desired percentage of the pathogen to be inactivated, the desired intensity from the UV light source, and the desired UV dose. According to any of the embodiments, the housing 111 has a height in the range of ¼ inch to 10 inches, a width in the range of ¼ inch to 10 inches, an outer diameter in the range of ¼ inch to 10 inches, an inner diameter in the range of ⅛ inch to 9¾ inches, a thickness in the range of ⅛ inch to 5 inches, and a length in the range of 1 inch to 50 feet.
According to any of the embodiments, at least a portion of the housing 111 is transparent. As shown in FIG. 2, the base portion of the conical-shaped housing 111 can be open (i.e., not covered) or can include a transparent lens 113. The transparent lens 113 can be made from a variety of materials including, without limitation, glass, glass including a rare earth element, or plastic. The material for the transparent lens 113 can also be designed such that amplification of the UV light emitted from the UV light source 112 occurs. By way of example, a glass including a rare earth element and a magnifying glass made from glass or a plastic (e.g., poly(methyl methacrylate) “PMMA ”) having a convex shape can cause amplification of the UV light emitted. The housing 111 can also be made entirely from a transparent material, for example as shown in FIG. 3.
The UV light-emitting device 110 also includes an ultraviolet (UV) light source 112 located within the housing 111, wherein the UV light source 112 emits ultraviolet light at a predetermined peak wavelength. The UV light source 112 can be a UV lamp. According to certain embodiments, the UV lamp is a UV light-emitting diode (UV-LED). Advantages to using a UV-LED lamp over mercury-vapor lamps include, but are not limited to, the lamp is less fragile, there is no warm-up time, there is no risk of mercury exposure, and the intensity of the UV light emission is constant for the duration of UV light emission. Other types of UV lamps and light sources can be used depending on the desired predetermined peak wavelength. For example, incandescent lamps, gas-discharge lamps, xenon arc lamps, deuterium arc lamps, mercury-xenon arc lamps, and metal-halide arc lamps can be used. One of ordinary skill in the art will be able to select the specific UV light source 112 based in part on the pathogens to be targeted in the HVAC system 100 and the peak wavelength required to inactivate the pathogens. The portion of the housing 111 that is transparent allows the emitted UV light to interact with air flowing through the HVAC system 100 in the direction D1; thus, inactivating the pathogen(s).
According to any of the embodiments, more than one UV light source 112 can be located within the housing 111. The more than one UV light sources can be connected in series. FIGS. 1 and 3 show a plurality of UV light sources contained within a transparent housing 111—commonly referred to as a “rope light.” If more than one UV light source is located within the housing, the peak wavelength emitted from each UV light source can be the same or different. The UV light-emitting device 110 can include a housing 111 that houses a first UV light source 112 a and a second UV light source 112 b emitting different peak wavelengths, for example as shown in FIG. 3. By way of example, the first UV light source 112 a can emit a peak wavelength of 222 nm, and the second UV light source 112 b can emit a peak wavelength of 270 nm. By way of another example, the first UV light source 112 a can emit a peak wavelength of 222 nm and the second UV light source 112 b can emit a peak wavelength of 254 nm. The UV light source 112 can also be a pulsed UV light source that emits a wide range of wavelengths, for example, from 200 to 320 nm. Although shown in FIG. 3 as the first and second light sources 112 a/112 b alternating, it is to be understood that a row of multiple first light sources can be connected series and a row of multiple second light sources can be connected in series in a different location of the same housing. By way of another example, a plurality of first light sources can be connected in series and a plurality of second light sources can be connected at the end of the first series—preferably, in order to share a common power source. Arrangements within the same housing as alternating, series, connected series, etc. of a third, fourth, and so on light sources may also be designed.
The peak wavelength emitted can be selected based in part on the specific pathogen that is targeted and that pathogen's sensitivity to the peak wavelength. It is to be understood that the wavelength emitted can be a range, for example, in the range of 260-268 nm. As used herein, the “peak wavelength” is defined as the single wavelength where the radiometric emission spectrum of the light source reaches its maximum. According to certain embodiments, the peak wavelength is in the UV-C range of 100-280 nm and the pathogens that are targeted are SARS-CoV-2 and influenza virus.
The HVAC system 100 can also include more than one housing 111. Any additional housings can be located within the same component of the HVAC system 100 or located within a different component of the HVAC system 100. By way of example and as shown in FIG. 1, a first housing 111 a can be located within the return air duct 121 and/or the return plenum 122, a second housing 111 b can be located within the supply plenum 125 and a supply air duct 127, and a third housing 111 c can be located within the supply plenum 125 and a different supply air duct 127. By way of another example, a first housing 111 a can be located within the supply plenum 125 and additional housings can be located within each of the supply air ducts 127. Additional housings may be useful to increase the combined UV dose of the UV light exposure to the air flowing through the HVAC system in the direction D1.
The total number and location of additional housings can be selected and designed based in part on the air flow rate through the HVAC system, the intensity of the UV light that is emitted from each UV light source, and the dimensions of the transparent portion of the housing inter alia. The peak wavelength that is emitted from the UV light sources located within the first, second, third, and so on housings can be the same or different. As used herein, the phrase “the same” regarding the peak wavelength means within (+/−) 5 nanometers of each other and are close enough to one another to be considered to target the same pathogen. As used herein, the phrase “different” regarding the peak wavelength means more than +/−5 nanometers of each other and are far enough apart from each other to be considered to target different pathogens. By way of example, the first housing 111 a can include one or more of a first UV light source 112 a that emits a peak wavelength of 222 nm, and the second housing 111 b can include one or more of a second UV light source 112 b that emits a peak wavelength of 270 nm. As discussed above, a single housing (e.g., the first housing 111 a) can house both a first UV light source 112 a and a second UV light source 112 b. There can also be more than two different UV light sources each emitting different peak wavelengths, for example a third UV light source, a fourth UV light source, etc.
As shown in FIGS. 1 and 3, for housings including a plurality of UV light sources that are connected in series—commonly referred to as a “rope light”—the housing 111 can be cylindrical or cubic in shape and made from a transparent, flexible material. The transparent, flexible material can be a heavy-duty plastic, such as polyvinyl chloride (“PVC”). In this manner, the housing 111 can curve to conform to the HVAC component without breaking. For example, air ducts generally curve and contain bends in order to connect return air ducts from a return vent to the return plenum or to connect supply air ducts from the supply plenum to supply vents. As can be seen in FIG. 1, a second housing 111 b and a third housing 111 c are located within the supply plenum 125 and supply air ducts 127.
The UV light-emitting device 110 can include a power source 114. The power source 114 can supply power to components of the device, such as the UV light source 112. The power source 114 can be any source, such as a direct supply and/or batteries. The plurality of housings 111 a/111 b/111 c can be connected in parallel to a common power source 114 or each housing that houses the UV light source 112 can have its own power source.
The intensity of the UV light source can vary or be predetermined. The UV light-emitting device 110 can be configured to provide a desired intensity. By way of example, in order to provide the desired intensity, the UV light-emitting device 110 can further include a wave amplifier (e.g., a mirror or plurality of mirrors or a magnifying glass), not shown. The wave amplifier can amplify the peak wavelength such that a greater number of pathogens are inactivated. The UV light-emitting device 110 can be designed such that a desired percentage of a targeted pathogen is inactivated. The desired percentage can be the percentage necessary to sanitize the air flowing through the HVAC system 100 in the direction D1. The desired percentage can also be 70%, 80%, or 90%. The intensity of the UV light source 112 can be selected and designed such that the desired percentage of the targeted pathogen is inactivated.
The UV dose can also vary and be selected such that the desired percentage of the targeted pathogen is inactivated. According to any of the embodiments, the UV dose emitted by the one or more UV light source(s) 112 is the D90 for the specific pathogen to be inactivated. According to any of the embodiments, the UV dose emitted by the one or more UV light source(s) 112 is at least 30 J/m², at least 40 J/m², or in the range of 30 to 60 J/m². The UV dose can be increased by increasing the intensity and/or the exposure time of the air flowing through the HVAC system 100 that is contacted by the UV light emitted from the UV light-emitting device 110. The exposure time can be increased, without limitation, by increasing the length of the transparent portion of the housing 111, increasing the number of housings, increasing the number of UV light sources 112, selecting the placement of numerous housings within different components of the HVAC system (e.g., the supply plenum and all supply air ducts), amplifying the peak wavelength emitted, and combinations thereof. By way of example, a first housing 111 a can be placed within the supply plenum 125 and can have a length in the range of 6 inches to 5 feet, a second housing 111 b can be placed within a primary supply air duct 127 whereby all other supply air ducts branch off from the primary supply air duct and can have a length selected to span some of or the entire length of the primary supply air duct, and a third housing 111 c can be placed within the return plenum 122 and can have a length ranging from 6 inches to 5 feet. The number of UV light sources 112 that are housed within each housing 111 can also range from 1 to 100, and the spacing of the UV light source 112 can be selected to inactivate the desired percentage of the targeted pathogen.
As discussed above, the UV light-emitting device 110 can be designed to inactivate a desired percentage of more than one type of pathogen. By way of example, one or more of a first housing 111 a can contain one or more of a first UV light source 112 a that emits a peak wavelength that targets a first pathogen, and one or more of a second housing 111 b can contain one or more of a second UV light source 112 b that emits a peak wavelength that targets a second pathogen. By way of another example, the same housing 111 can contain one or more of a first UV light source 112 a and one or more of a second UV light source 112 b, wherein the first and second UV light sources emit different peak wavelengths that target a first and second pathogen, respectively, for example as shown in FIG. 3. Other combinations are also possible, and one of ordinary skill in the art can design the UV light-emitting device 110 to target a multitude of different pathogens based on the disclosures herein.
The UV light-emitting device 110 can include an attachment component (not shown). The attachment component can allow the various components (e.g., the housing 111) of the UV light-emitting device 110 to be removably secured to a component of an HVAC system 100. By way of example, for a rope-light-type housing, the UV light-emitting device 110 can include clips or tape or VELCRO® for removably securing the rope light housing to an inside perimeter of an air duct or a plenum. By way of another example in a motor vehicle, the UV light-emitting device 110 can include clips or tape or other attachment means for removably attaching the housing to an air inlet and/or hoses that are connected to cabin vents. According to any of the embodiments, the housing 111 is permanently or removably attached to the component of the HVAC system 100 such that the UV light emitted from the UV light source 112 is directed towards air flowing through the HVAC system 100. Accordingly, the bottom portion of the housing 111 at the location of the first and second UV light sources 112 a/112 b shown in FIG. 3 for example would be located along an inner perimeter of the HVAC system such that the UV light is directed into the inside of the HVAC component, for example, an air duct. In this manner, the UV light is directed to contact air as it moves through the HVAC system 100 instead of directed to contact the HVAC component and not the air.
The UV light-emitting device 110 can include an activation switch (not shown). The activation switch can activate the UV light source 112 such that the UV light source 112 emits the peak wavelength. The activation switch can be located on any portion of the UV light-emitting device 110, any component of the HVAC system 100, or a different location, for example, a thermostat or activation plate on a wall. The activation switch can be manually activated by turning the activation switch to an “on” position directly on the activation switch or remotely, for example, via a remote control. Activation of the UV light source 112 can also be accomplished via a relay switch that triggers and activates the UV light source only when air is flowing through the HVAC system 100, for example, when the fan of the HVAC system is turned on. By way of example, the UV light source 112 can be activated via a low-voltage signal from an HVAC control board when air is flowing through the HVAC system. By way of another example, the UV light source 112 can be constantly emitting UV light if the UV light source is wired directly to the HVAC system's low-voltage transformer 126. In certain embodiments, the UV light source 112 does not continuously emit UV light.
Therefore, the present invention is well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. The particular embodiments disclosed above are illustrative only, as the present invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is, therefore, evident that the particular illustrative embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the present invention.
As used herein, the words “comprise,” “have,” “include,” and all grammatical variations thereof are each intended to have an open, non-limiting meaning that does not exclude additional elements or steps. While compositions, systems, and methods are described in terms of “comprising,” “containing,” or “including” various components or steps, the compositions, systems, and methods also can “consist essentially of” or “consist of” the various components and steps. It should also be understood that, as used herein, “first,” “second,” and “third,” are assigned arbitrarily and are merely intended to differentiate between two or more housings, UV light sources, etc., as the case may be, and does not indicate any sequence. Furthermore, it is to be understood that the mere use of the word “first” does not require that there be any “second,” and the mere use of the word “second” does not require that there be any “third,” etc.
Whenever a numerical range with a lower limit and an upper limit is disclosed, any number and any included range falling within the range is specifically disclosed. In particular, every range of values (of the form, “from about a to about b,” or, equivalently, “from approximately a to b,” or, equivalently, “from approximately a-b”) disclosed herein is to be understood to set forth every number and range encompassed within the broader range of values. Also, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee. Moreover, the indefinite articles “a” or “an,” as used in the claims, are defined herein to mean one or more than one of the element that it introduces. If there is any conflict in the usages of a word or term in this specification and one or more patent(s) or other documents that may be incorporated herein by reference, the definitions that are consistent with this specification should be adopted.

Claims

What is claimed is:

1. An ultraviolet light-emitting device for use in a heating, ventilation, and air conditioning system, the device comprising:

a first housing located within a component of the heating, ventilation, and air conditioning system, wherein at least a portion of the first housing is transparent;

a first ultraviolet light source located within the first housing and adjacent to the portion of the transparent housing, wherein the first ultraviolet light source emits ultraviolet light at a pre-selected peak wavelength; and

a power source for supplying power to the first ultraviolet light source.

2. The ultraviolet light-emitting device according to claim 1, wherein the housing has a conical shape.

3. The ultraviolet light-emitting device according to claim 2, wherein a portion of the housing is opaque.

4. The ultraviolet light-emitting device according to claim 3, wherein a base of the conical-shaped housing is open or is covered by a transparent lens.

5. The ultraviolet light-emitting device according to claim 4, wherein the transparent lens has a convex shape, and wherein the transparent lens amplifies the ultraviolet light emitted from the first ultraviolet light source.

6. The ultraviolet light-emitting device according to claim 1, wherein the housing has a cylindrical shape, and wherein the housing is completely transparent.

7. The ultraviolet light-emitting device according to claim 1, wherein the first ultraviolet light source is an ultraviolet lamp.

8. The ultraviolet light-emitting device according to claim 7, wherein the ultraviolet lamp is an ultraviolet light-emitting diode lamp.

9. The ultraviolet light-emitting device according to claim 1, wherein the first housing further comprises a second ultraviolet light source.

10. The ultraviolet light-emitting device according to claim 9, wherein the first ultraviolet light source and the second ultraviolet light source emit a peak wavelength that are the same.

11. The ultraviolet light-emitting device according to claim 9, wherein the first ultraviolet light source and the second ultraviolet light source emit a peak wavelength that are the different.

12. The ultraviolet light-emitting device according to claim 1, wherein the peak wavelength is in the UV-C range of 100-280 nanometers.

13. The ultraviolet light-emitting device according to claim 1, further comprising:

a second housing located within a component of the heating, ventilation, and air conditioning system, wherein at least a portion of the second housing is transparent;

a second ultraviolet light source located within the second housing and adjacent to the portion of the transparent housing, wherein the second ultraviolet light source emits ultraviolet light at a pre-selected peak wavelength; and

a power source for supplying power to the second ultraviolet light source.

14. The ultraviolet light-emitting device according to claim 13, wherein the second housing is located within the same component of the heating, ventilation, and air conditioning system as the first housing.

15. The ultraviolet light-emitting device according to claim 13, wherein the second housing is located within a different component of the heating, ventilation, and air conditioning system from the first housing.

16. The ultraviolet light-emitting device according to claim 13, wherein the peak wavelength that is emitted from the first ultraviolet light source is the same as the peak wavelength that is emitted from the second ultraviolet light source.

17. The ultraviolet light-emitting device according to claim 13, wherein the peak wavelength that is emitted from the first ultraviolet light source is different from the peak wavelength that is emitted from the second ultraviolet light source.

18. The ultraviolet light-emitting device according to claim 1, wherein the ultraviolet dose that is emitted from the ultraviolet light-emitting device is selected such that a desired percentage of a targeted pathogen is inactivated.

19. The ultraviolet light-emitting device according to claim 18, wherein the desired percentage is greater than or equal to 70%.

20. The ultraviolet light-emitting device according to claim 18, further comprising an amplifier that amplifies the intensity of the ultraviolet light emitted from the first ultraviolet light source.