GB2512708A - Ultraviolet monitoring systems, methods, and devices - Google Patents

Abstract

A method of maintaining an ultraviolet air treatment system comprises: detracting light output from an ultraviolet light source at multiple points in time; when the light output drops to a first level, outputting an indication that the ultraviolet light source needs to be cleaned; in response to a detection that the UV light source has been cleaned and a detection of a light output below a second level at a time approximately contemporaneous with the detection that the ultraviolet light source has been cleaned, outputting an indication that the ultraviolet light source needs to be changed. The at least one ultra violet light source may include multiple lamps in a ventilation plenum, and may include multiple lamps in a chamber downstream of at least one kitchen exhaust hood.

Description

Ultraviolet Monitoring Systems, Methods, and Devices

Cross Reference to Related Aøpfications

The present application claims the benefit of US provisional application 61/419,867 for Ultraviolet Monitoring Systems, Methods, and Devices," which was filed 5 December 2010, the entirety of which is hereby incorporated by reference.

Field

The present invention is directed to maintenance of filtering systems that use ultraviolet light to degrade or sterilized contaminants.

Background

The present invention is directed to maintenance of filtering systems that use ultraviolet fight to degrade or sterilized contaminants.

Summary

In embodiments, a control system tor a UV air treatment system, especially one used for cleaning a fume stream such as in a kitchen exhaust system, detects a need for cleaning maintenance on the UV light source based on changes in Eight intensity. The system further detects the light intensity each time the UV hght source is cleaned to determine if the drap in

I

intensity alter cleaning indicates that the UV light source should be replaced.

The cleaning and replacement requirements are Indicated automaticaHy by a user interface.

Objects and advantages of embodftnents of the disclosed subject matter will become apparent fron the following description when considered in conjunction with the accompanying drawings.

Brief Description of the Drawings

Embodiments will hereinafter be described in detail below with reference to the accompanying drawings, wherein like reference numerals represent hke elements The accompanying drawings have not necessarily been drawn to scale. Where applicable, some features may not be iflustrated to assist in the description of underlying features.

Fig. I shows an ultraviolet air treatment system according to embodiments of the disclosed subject matter.

Fig. 2 illustrates a time series of intensity measurements with corresponding control system output mapped thereto according to embodiments of the disclosed subject matter.

Fig. 3 shows a flow chart of a procedure for indicating maintenance requirements for a UV light source according to embodiments of the disclosed subject matter.

Fig, 4 shows a flow chart of a procedure for indicating maintenance requirements for a UV light source according to further embodiments of the disclosed subject matter.

Hg. 5 is a variation of Fig. 2 illustrating a difieront scheme for responding to intensity level changes.

Fig. 6 iflustrates an imaging system for acquiring intensity data from a UV light source including multiple amps.

Fig. 7 is a flow chart showing a portion of a procedure that may be used in any of the embodiments described.

Fig. 8 shows an output display example according to embodiments of the disclosed subject matter.

Fig. 9 illustrates a scheme for estimating cleaning points and replacement points for maintaining UV light sources.

Detailed Description

In some applications, ultraviolet (UV) sources such as lamp bulbs tend to get dirty. For example, in one application, in kitchen exhaust systems, oil droplets appear in grease smoke from kitchen, such as a commercial kitchen.

Grease filters are not entirely effective to remove grease droplet making up the majority of the pollutants in such smoke because they only capture the larger droplets. UV can be used to degrade much finer droplets making up grease smoke. To provide a treatment, UV lamps must be exposed to grease smoke However even fire part'cles tend to stick to surfaces of the UV lamps reducing their output.

The present invention is an intelligent detection and maintenance advisor device that monitors the intensity of UV sources over time and indicates to maintenance operators when to clean UV sources that have become dirty and when to replace the sources based on a historical record of the detected intensity.

Referring to Fig. 1 a ventilation treatment device 104 receives polluted air 118. The polluted air flows through the ventilation treatment device 104 where the polluted air 118 is exposed to light from a UV source 10 The treated air 120 then exist the vent!lation treatment device 104. A sensor 102 continually monitors the intensity of light from the UV source 10 by detecting some of the light 112 that passes to the sensor 102. In an embodiment, the sensor 102 is protected from contamination by a flush stream of clean air 116 forced by a fan 114 rito tnc ventilation treatment device 1049 thereby preventing pollutants in the ventilation treatment device 104 from accumulating on the sensor 102.

A controller 100 regularly polls the sensor 102 and creates a record, which is stored in a non-volatile memory 108 e.g, a flash memory), of readings from the sensor 102. Referring now also to Fig. 2, a (sawtooth-shaped) curve 40 shows a history of the light intensity indicated by the sensor 102 according to axes of inensrty versus time A new UV source 10 generates an output as indicated at 1. When light from the UV source falls below a threshold intensity 39, as indicated by point 11, an indication is generated by the controller 100 to clean the UV source 10. The new UV source may be the result of a change of an expired UV source or more than one expired UV source. The indication may be output on a user interface 106, for example, an LCD display or a lamp labeled "Clean." The comparison between a stored threshold level and the detected level may be made by the controller 100. The ihreshold level may be obtained upon replacement of the UV source 10 from a percentage calculation made by the controller, for example the threshold may be 50% of the intensity of the new UV source 10 The cleaning of the UV source 10 results in a higher intensity as indicated at 2, but the intensity is lower than the intensity 1 of a new lamp as indicated. As the cleaned UV source 10 is used its intensity tails again to the threshold level 39 as indicated at 12 whereupon the signal to clean is again generated as indicated at 22. The cycle repeats with an indIcation to clean being output at 23 and 24 corresponding to intensity points 14 and 15. The corresponding clean intensity levels, 3,4, and 5 progressively diminish with time. At the time when the threshold level is again met at point 16, a indication 26 to replace the LJV source is output at which time the intensity is restored to the level at point 6. In addition, the time between intensity threshold crossings may diminish progressively as well providing an alternatwe indicator of the need to replace tie UV source The ind'cation to clean may be determrned by the intensity of the most recent new cycle, for example the percentage difference between the stored intensity value 2 and threshold intensity 39. If the difference exceeds a predetermined amount, the controller 100 generates a signal to clean. If it is below this predetermined level the indication to replace the UV source, e.g., a bulb, is generated-The cycle then repeats through commands 26, 27, 28 and soon coinciding with dirty points 18, 18, 19 to restore output to levels at clean points 7. 8, and 9. It should be clear that this profile can be repeated indefinitely. The predetermined intensity values may be stored in the nonvolatile storage 108. Other data than the intensity values can be stored.

For example, the elapsed time since a cleaning indication may be stored.

When a cleaning or replacement indication is output, the system may wait for an Indication that the maintenance operation has been performed.

For example, after cleaning the UV source, a command may be input by a user through the user ntedace to reset the maintenance ndication currently being output (clean or replace). Alternatively, the system may detect the change in intensity and reset itself, For example, an upper threshold may be defined which, when exceeded, indicates the UV source has been properly cleaned. Another upper threshold, higher than the other, may be defined indicating the UV source has been properly replaced. In response to one or both, the system may update the status of the UV source to a cleaned or replaced UV source. Another way the controller may be configured to reset the status of the UV source is to detect a positive change in the intensity of greater [han a predefined amount. So rather than having a particular threshold intensity that the light source exceeds, the reset is indicated when the positive change in intensIty since a last recorded intensity is greater than a predelined amount.

Referring now to Fig. 3, a flow chart shows a procedure for outputting maintenance steps of cleaning and replacing UV light sources. Light output from a UV source is detected duri'ig normal operation of the ventilation system at 314. At 318, from the current level of the light output measured or from an historical trend the need for either a cleaning operation or a replacement operation is determined according to any of the critena descrioed elsewhere in the present specification. At 320, if a maintenance output is indicated, control proceeds to S22 otherwise it loops back to 814. At S22, the type of control output is determined and the corresponding output is generated at 824 or 325, respecdvely after which control proceeds to 810 or 311, respectively as indicated. At Si U and 511, the completion of the respective mairflenance action is detected, or a command received indicating its completion, and an indication stored at Si 2 that the maintenance is done The Si 2 operation may include storing a value of the intensity after a cleaning, or other data responsive thereto, for purposes of determining whether a replacement operation is, or will be, required according to criteria of any of the appllcabie embodiments described herein.

Referring now to Fig. 4, a flow chart shows a further procedure for outputting maintenance steps of cleaning and replacing UV light sources. The controller determines whether the elapsed time since a prior lamp check is beyond predefined interval TC at 8214. Ii not the control loops, otherwise at S216 a procedure s performed in wriich the light output from each lamp of multiple amps is performed to acquire the output of each lamp. At 5218, the status of each lamp is determined according to criteria discussed in the present specf cation If maintenance output indicator is required as determined at 3220, control proceeds to 5222 otherwise it loops back to 8214. At 8222, the type of control output is determined and the corresponding output is generated at 8224 or S225, respectively after which control proceeds to 5210 or S21 i, respectively as indicated. At 5210 and 5211, the completion of the respective maintenance action is detected, or a command received indicating its completion, and an indication stored at 8212 that the maintenance is done. The 8212 operation may include storing a value of the intensity after a cleaning, or other data responsive thereto, for purposes of determining whether a replacement operation is, or will be, required according to criteria of any of the applicable embodiments described herein.

Referring to Fig. 5, the system may allow operation of the lamp if a cleaning operation is required, except that the output of the user interface may cont nue to indicate a need for cleaning 1 is system may also prevent operation of the hood if there is no response after an output of a cleaning indication. The system may provide a grace period of a predefined period of time or a predefined number of startups of the ventilation system after the first output of an indication to clean or replace. The grace period may be different for each of the indications, namely clean or replace In an embodiment, the system provides a warning indication of a need for clean or replace after passing a first threshold intensity 51 but only begin enforcing the maintenance operation by preventing the use of the ventilation system after the intensity drops through a second, lower threshold 52.

Referring to Figs S and 7 in any of the embodiments, the condition of each amp 400 in an array 402 is imaged simultaneously or ndividua!ly by an imag ng device such as a camera In this way, the Intensity of each lamp can be acquired separately by processing the image and segmenting the light intensity of eacn lamp 400 respectively As indicated at S404 and S406, in response, the status (here indicated as a predicted time till next required action) of each lamp can be listed on an output as a separate indication. For example, a schematic of Fig 8 can be generated by a UI with predicted hours till next cleaning or predicted hours to replacement indicated for each lamp 400 as indicated at 408. Alternatively the data for the predicted time till indicated action can be listed in a data packet transmitted to a central controuer as discussed above.

In any of the embodiments, instead of an output of an indication of a need to clean or replace, the control system can generate a prediction of when the lamps will next need to be cleaned and when they will next need to be replaced. Such a system may provide an output indication of both pieces of information. This information may be output as a control signal to a central ventilation monitoring system so that the controller for the UV treated system does not need to have its own output display or other output terminal An Internetconnected control system can automatically order a set of replacement sources when a predefined time is indicated between the current time and the predicted time for replacement. This feature may be implemented by providing the controller and software that runs on a general purpose computer (Fig. 1, 107) or one that is connected to a general control system (Fig. 1 GPCS 101). The latter may be a part of, for example, a control system for a commercial kitchen or the HVAC system for a building and may use a standard protocol to output status information and/or recommended actions to the general purpose control system.

In any of the foregoing embodiments, the status of the UV light source may be inferred from othr oetected data For example, the surface pattern of light of a lamp may be compared in terms of uniformity or in terms of a particular pattern of intensity over its surface such that the light distribution, rather than the overall intensity indicates the condition of the lamp. For example an irregular pattern of hght or one or light blocking blobs may be imaged by a suitable camera to indicate foung by fumes or aerosols in the ventilation air, for example.

In any of the embodiments, the control system may be configured to detect other anomalies in the output of the UV light source. The decay rate of intensity 10 the LIV sowce may provide a useful indicator of the operating status of a filter (indicated at 127 in Fig. 1) upstream of the UV sources. For example, in a kitchen exhaust system, typically grease filters are used to trap particulates before further treatment by a UV source lithe grease filters are left out, not properly installed, or functioning poorly, the rate of fouling of the UV source may indicate this This attendng abnormally high rate of diminution of intensity may be indicated in any of the described systems according to any of the information output schemed described above or elsewhere.

In any of the disclosed embodiments, the faUure of a lamp or power supply may be detected and indicated by any of the disclosed UI systems as well as diagnosis of performance and maintenance actions as discussed In a representative operating scenario, a ventilation system is started after UV sources that were just replaced. The ventilation system is operated continuously or in multiple cycles (such as multiple mealtime cycles of operation of a kitchen or diurnal cycles of an office ventilation system). At one or more times during each operating cycle or at times during continuous operation of a ventilation system that does not cycle but runs continuously, the UV source intensity is acquired (or otherwise acquired for example, the light sources may be imaged according to the respective embodiment). In embodiments, the UV source or each olement (e g lamp) may have a predicted status, for example, representable as operating hours till cleaning and operating hours tUl replacement. These values may be updated based on historical trends in the intensity data. In other embodiments, the intensity data may be stored in original for and used at any selected time to generate a prediction or "action required" output such as an indication to clean or an indication to replace one amp or a single UV source. Instead of estimated operating time to next cleaning and/or replacement, the elapsed time, based on predicted usage, may be calculated and output.

In the operating scenario, a succession of status indications may be generated responsively to a request or automatically. For example, the estimated time to next cleaning may be continuously output or output responsively to the crossing of a threshold (ag, threshold 51 of Fig, 5) or output according to an expected time until the need for the maintenance operation.

Referring to Fig. 9. estimating status or maintenance events by the controller may be done using any of a variety of techniques For example the expected time until a maintenance operation may be derived from a line of best t between respective points Ir Fig 9, two points one representing intensity after an actual cleaning or replacement 602, and another representing intensity after an actual cleaning 604 allow a line of best fit (Jf there were more points it would be a line of best I it according least squares or other scheme) to be drawn and extrapolated to a predicted threshold 612 for replacement, thereby yielding a predicted replacement point 610. In the same way multiple intensity measurements occurring at various times during operation or during calibration perIods 623 can be extrapolated to an ii predicted cleaning point 608. The time scale may be operating hours or elapsed actual time.

According to embodiments, the disclosed subject matter includes a method of maintaining an ultra-violet air treatment system. The method includes detecing an intensity of at east one ultraviolet light source at successive points in time during operation thereof in an air treatment system.

The method further includes applying signals representing the intensity to a controller and storing data responsive to the detected intensities in a data store. The controfler, at a first time, on a user output terminal, generates an indication that t'e at least one ultraviolet light source requires cleaning The controller, at a second time, on the user output terminal, generates an indication that the at east ne ultraviolet light source requires replacement.

The controller receives a maintenance indication where the maintenance indication is a signal indicating at least one of the completion of a cleaning of the ultraviolet light source and a replacement of the at least one ultraviolet light source. The generating operation that generates an indication that the at least one ultraviolet light source requires cleaning is responsive to the maintenance indication and stored data responsive to the intensity of the at least one ultraviolet light source immediately after maintenance indication.

According to embodiments, the disclosed subject matter includes a method of maintaining an ultra-violet air treatment system. The method includes detecting an intensity of at least one ultraviolet light source at successive points in time during operation thereof in an air treatment system.

The method further includes applying signals representing the intensLty to a controller and storing data responsive to the detected intensities in a data store. The controfler, at a first time, on a user output terminal, generates an indication that the at east one ultraviolet light source requires cleaning. The controller, at a second time, on the user output terminal, generates an indication that the at east one ultraviolet light source requires replacement.

The controller receives a maintenance indication whore the maintenance indication is a signal indicatirg at least one of the completion of a cleanirg of the ultraviolet light source and a replacement of the at least one ultraviolet light source The generating an -dication that the at least one ultraviolet light source requires replacing is responsive to the maintenance indication and stored data responsive to the intensity of the at least one ultraviolet light source at multiple points ii tme such that the indication that the ultrawolet lamp requires replacing is generated if multiple maintenance indications have been received by the controller indicating cleaning of the at least one ultraviolet light source According to embodiments, the disclosed subject matter includes a method of maintaining an ultra-violet air treatment system. The method applies to a system that includes a controller where the controller has at least one sensor and an output device and is configured to perform the method.

The method includes detecting an intensity of at least one ultraviolet light source at successive points in time. The method further includes receiving an indication that the at least one uRraviolet light source has just been cleaned.

When the detected intensity is above a first threshold upon a first detecting after a receiving, the controller outputs no maintenance indication. When the detected intensity is below the first threshold upon a first detecting after a receiving, the controller outputs a maintenance indication indicating to replace the ultraviolet tight source. When the detected intensity is below a second threshold upon a detecting subsequent to a first detecting after a receiving, the controller outputs a maintenance indication indicating to dean the ultraviolet light source.

In the above method, the first threshold may correspond to a tower intensity than the first threshold.

According to embodiments, the disclosed subject matter includes a method of maintaining an ultra-violet air treatment system, the system including a controller. The controller has at least one sensor and an output device and is configured to perform the method which includes detecting an intensity of at least one ultraviolet light source at successive points in time.

The method further includes receiving an indication that the at least one ultraviolet light source has just been cleaned. When the detected intensity is above a threshold upon a first detecting after a receiving, the controfler outputs no maintenance indication, When the detected intensity is below the threshold upon a first detecting after a receiving, the controller outputs a manterance indication indicating to replace the ultraviolet light source When the detected intensity is below the lhrcshold upon a detecting subsequent to a first detecting after a receiving, the controller outputs a maintenance indication indicating to clean the ultraviolet light source.

in any of the methods, the at least one ultraviolet light sources may include multiple lamps in a ventilation plenum. The at least one ultraviolet light sources may include multiple amps in a chamber downstream of at least one kitchen exhaust hood. The controller may include a programmable digital controller.

According to embodiments, the disclosed subject matter includes a system nekiding an exhaust hood and a controfler adapted or performing any of the methods described herein. According to embodiments, the disclosed subject matter includes a controiler configured for performing any of the recited methods. According to embodiments, the disclosed subject matter includes a computer readable medium having instructions recorded thereon for performing any of the above recited methods The foregoing medium may include instructions wherein the air treatment system includes a kitchen exhaust system. The foregoing controller may be configured for operation in a system that indudes a kitchen exhaust system The air treatment system may nclude a kitchen exhaust system in any of the foregoing embodiments. The maintenance indication may include an estimate of time until the maintenance is required.

According to embodiments, the disclosed subject matter includes a method of maintaining an ultra-violet air treatment system. The method includes detecting light output from an ultraviolet hght source at multiple points in time, From a first trend in the data, the data representing multiple instances of the detecting, the a required first maintenance action is determined to elevate the light output from the light source and outputting an indicaUon Of the required maintenance action. The method further includes detecting a performance of the first maintenance action. From a second trend in the data representing multiple instance of the detecting in combination with the detecting a performance of the first maintenance event the method determines a required second maintenance action and outputting an indication of a need for the second maintenance action responsively thereto.

The detecting a performance may include detocthig a change in light output indicating the completion of the first maintenance action. The first maintenance action may include cleaning the ultraviolet light source. The second maintenance action may include replacing or repairing the ultraviolet light source. The outputting may include displaying a message on a user interface indicting, respectively, the need for the first and second maintenance actions. The detecting a performance may include receiving a user input indicating the completion of the first maintenance action.

According to embodiments, the disclosed subject matter includes a method of maintaining an ultra-violet air treatment system. The method includes detecting light output from an ultraviolet light source at multiple points in time and when the light output drops to a first level, outputting an indication that the ultraviolet light source needs to be cleaned. In response 10 a detection that the ultraviolet light source has been cleaned and a detection of a light output below a second level at a time approximately contemporaneous with the detection that the ultraviolet light source has been cleaned, an indication that the ultraviolet light source needs to be changed is output by the controller The outputting of an ndicatior that the ultraviolet light source needs to be changed may be performed in response to a subsequent to the time approximately contemporaneous with the detection that the ultraviolet light source has been cleaned. The at least one ultraviolet light sources may include multiple lamps in a ventilation plenum. The at least one ultraviolet light sources may include multiple lamps in a chamber downstream of at least one kftchen exhaust hood. The controller may be a programmable digital controller According to enbodiments, the aisclosed subject matter includes a system including an exhaust hood and a controfler adapted for performing any of the methods or a cortrollor configured for performing any of the methods or a computer readable medium having instructions recorded thereon for performing any of the methods.

It will be appredated that the modules, processes, systems, and sections described above ca.n be implemented in hardware, hardware programmed by software, software instruction stored on a non-transitory computer readable medium or a combiriatFon of the above. For example, a method for indicating a maintenance operation can be implemented, for example, using a processor configured to e*ecute a sequence of programmed instructions stored on a non-transitory computer readabk medium. For example me processor can include but not be hn'ited to, a personal computer or workstation or other such computing system that includes a processor, microprocessor, microcontrotler device, or is comprised of control logic including integrated circuits such as, for example, an Application Specific Integrated Circuit (ASlC). The instructions can be compiled from source code instructions provided in accordance with a programming language such as Java, C++, C#,net or the like. The instructions can also comprise code and data objects provided in accordance with, for example, the Visual SasicTM language, LabVIEW, or another structured or object-oriented programming language The sequence of programmed instructions and data associated therewith can be stored in a non-transitory computer-readable medium such as a computer memory or storage device which may be any suitable memory apparatus, such as, but not hmited to read-only memory (ROM, programmable read-only memory (PROM), electrically erasable programmable read-only memory (EEPROM), random-access memory CRAM), flash memory, disk drive and the like.

Furthermore, the modules, processes, systems, and sections can be implemented as a single orocessor or as a distributed processor Further it should be appreciated that the steps mentioned above may be performed on a single or distributed processor (single and/or multi-care). Also, the processes, modules, and sub-modules described in the various figures of and for embodiments above may be distributed across multiple computers or systems or may be co-located in a single processor or system. Exemplary structural embodiment alternatives suitable for implementing the modules, sections, systems, means, or processes described herein are provided below.

The modules, processors or systems described above can be implemented as a programmed general purpose computer, an electronic device programmed wUh microcode, a hard-wired analog logic circuit, software stored on a computer-readable medium or signal, an optical computing device, a networked system of electronic and/or optical devices, a special purpose computirg device an integrated circuit device, a semiconductor chip, and a software module or object stored on a computer-readable medium or siqnal, for example.

Embodiments of the method and system (or their sub-components or modules), may be implemented on a general-purpose computer, a special-purpose computer, a programmed microprocessor or microcontroller and peripheral integrated circuit element, an ASIC or other integrated circuit, a digital signal processor, a hardwired electronic or logic circuit such as a discrete element circuit, a programmed logic cimuit such as a programmable logic device (PLD), programmable logic array (PLA), field-programmabe gate array FPGA), programmable array logic (PAL) cevice, or the hke lr general, any process capable of implementing the functions or steps described herein can be used to implement embodiments of the method, system, or a computer program product (software program stored on a non-transitory computer readable medium).

Furthermore, embodiments of the disclosed method, system, and computer program product may be readily implemented, fully or partially, in software using, for exampe, object or object-oriented software developrrent environments that provide portable source code that can be used on a variety of computer platforms. Alternatively, embodiments of the disclosed method, system, and computer program product can be implemented partially or fully in hardware using, for example, standard logic circuits or a very-large-scale integration (VLSI) design. Other hardware or software can be used to implement embodiments depending on the speed and/or efficiency requirements of the systems, the particular funcUon, and/or particular software or hardware system, microprocessor, or microcomputer being utilized.

Embodiments of the method, system, and computer program product can be implemented in hardware and/or software using any known or later developed systems or structures, devices and/or software by those 01 ordinary skill in the applicable art from the function description provided herein and with a general basic knowledge of ventilation controt and/or computer programming arts.

Moreover, embodiments of the disclosed method, system, and computer program product can be implemented in software executed on a programmed general purpose computer, a special purpose computer, a microprocessor, or the like.

It is, thus, apparent that there is provided, in accordance with the present disclosure, systems, methods, and devices monitoring an ultraviolet air treatment apparatus. Many alternatives, modifications, and variations are enabled by the present disclosure. Features of the disclosed embodiments can be combined, rearranged, omitted, etc., within the scope of the invention to produce additional embodiments. Furthermore, certain features may somefinies be used to advantage without a corresponding use of other features. Accordingly, Applicants intend to embrace all such alternatives, modifications, equivalents, and variations that are within the spirit arid scope of the present invention.

Claims (6)

1. CLAIMS1, A method of maintaining an ultra-violet air treatment system, comprising: detecting light output from an ultraviolet light source at multiple points in S time; when the light output drops to a first level, outputting an indication that the ultraviolet light source needs to be cleaned; in response to a detection that the ultraviolet light source has been cleaned and a detection of a light output below a second level at a time approximately contemporaneous with the detection that the ultraviolet light source has been cleaned, outputting an indication that the ultraviolet light source needs to be changed.
2. 2. The method of c'aim I. wherein the outputting an indication that the ultravio'et light source needs to be changed is performed in response to a subsequent to the time approximately contemporaneous with the detection that the ultraviolet light source has been cleaned.
3. 3, A method as in claim 1 or claim 2. wherein the at least one ultraviolet light sources includes multiple lamps in a ventilation plenum.
4. 4, A method as in claim I. claim 2 or claim 3. wherein the at east one utravioet light sources includes multiple lamps in a chamber downstream of at least one kitchen exhaust hood.
5. 5, A method as in any of claims 1 to 4. wherein the controller is a programmable digital controller.
6. 6. A system including an exhaust hood and a controller adapted for performing the method of any of claims Ito 5, 7, A controller configured for performing the method of any of claims 1 to 5.S. A computer readable medium having instructions recorded thereon for performing the method of any of daims I to 5,