Abstract:
A light fixture includes a plurality of fluorescent bulbs wherein a light intensity of each of the plurality of fluorescent bulbs is related to the operating temperature of the fluorescent bulbs, a sensor for sensing a physical parameter related to the light intensity, and a circuit adapted for monitoring the sensor and controlling the operating temperature of the fluorescent bulbs to maintain the operating temperature of the fluorescent bulbs within a range having a lower temperature and an upper temperature. A method of maintaining light intensity of fluorescent bulbs in an environmental chamber includes monitoring a physical parameter associated with the light intensity of the fluorescent bulbs in an environmental chamber and adjusting temperature of the fluorescent bulbs in the environmental chamber to maintain an optimum light intensity of the fluorescent bulbs in the environmental chamber.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to a temperature controlled light fixture, such as, but not limited to a temperature controlled light fixture for use in environmental chambers. Environment chambers are used for various purposes including plant growth, incubation, germination and other purposes. The term “environmental chamber” is intended to include plant growth chambers, germinators, incubators, and other variations of environmental chambers, as it is to be appreciated that controlled environment chambers are used for numerous purposes. One common application for these chambers is plant growth research, where parameters such as temperature, light, and humidity (as well as other parameters such as CO 2 ) are tightly controlled. The specific combination of environmental conditions controlled may be related to the specific purpose of the environmental chamber. 
         [0002]    Light is one of the most important parameters studied in the field of plant growth research as it is a primary component in the process of photosynthesis. In some species of plants it is critical to have very high and very stable light irradiance (typically 1000 μmoles/m 2 /sec) throughout the entire chamber temperature operating range (typically about 4° C. to 45° C.). 
         [0003]    Fluorescent lamps tend to be the light source of choice for plant growth researchers as they are inexpensive, and very common. The drawback to fluorescent lighting is that the technology is suited for a wider application base such as residential and commercial lighting, where the performance requirements are not as stringent as those for plant growth. Thus, it appears that fluorescent lamp and ballast manufacturers have little incentive to improve their lamps to meet the specific needs of plant growth research. Thus, problems remain with fluorescent lighting for use in environmental chambers. 
         [0004]    One such problem is that fluorescent bulbs are sensitive to the temperature of the ambient environment in which they are operating. This is due to the primary application for which they are designed (residential settings tend not to have large temperature changes). Typically there is an optimal ambient temperature at which a bulb operates at peak efficiency (i.e. Lumens/Watt—or Light Intensity per Energy Consumption). The optimal bulb temperatures are specific to bulb-type. As ambient temperatures move away from this optimal point (either higher or lower) the lamps become less efficient. For each bulb type, manufacturers supply Temperature vs. Intensity curves. 
         [0005]    Researchers rely on consistent and predictable conditions within controlled environments, and currently no one in the industry has developed a solution which optimizes lamp efficiency, and provides stable lamp outputs over a wide range of temperatures (the typical temperature range for a lighted environment is approximately 4° C. to 45° C.). 
         [0006]    Up to this point, light fixtures have been developed (often with complete refrigeration systems) with controls which remove excess heat inside the fixture. The purpose of these systems was to remove the heat from the lamps as such heat negatively affects temperature within the environmental chamber. It should also be noted that the improvements to fluorescent light fixtures as discussed below are not just significant to the plant growth research industry. Other applications of this technology can benefit from the improvements provided by the present invention. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    Therefore, it is a primary object, feature or advantage of the present invention to improve over the state of the art. 
         [0008]    It is a further object, feature, or advantage of the present invention to monitor and control the light intensity of fluorescent lamps to maintain light intensity at or near optimum conditions in environmental chambers. 
         [0009]    It is a still further object, feature, or advantage of the present invention to manage or control heating and cooling of fluorescent lamps in order to control the light intensity of the fluorescent lamps. 
         [0010]    Yet another object, feature, or advantage of the present invention is to provide for the use of temperature sensitive fluorescent lamps, such as, but not limited to T5 lamps in environmental chambers. 
         [0011]    A further object, feature, or advantage of the present invention is to provide for stable light intensity from fluorescent lamps regardless of ambient temperature conditions in an environmental chamber. 
         [0012]    A still further object, feature, or advantage of the present invention is the ability to use heat produced naturally by lamps and ballasts to serve as a heat source for maintaining the required optimal temperature inside the light fixture so as to use previously unwanted heat to produce a positive on lighting and energy consumption characteristics of the light fixture. 
         [0013]    Another object, feature or advantage of the present invention is to increase efficiency of environmental chambers which require high light levels at low ambient temperatures such that additional fluorescent lamps do not necessarily need to be added to light fixtures to compensate for the loss in efficiency at low ambient temperatures. 
         [0014]    Yet another object, feature, or advantage of the present invention is to increase efficiency of an environmental chamber by using less current to power ballasts and bulbs. 
         [0015]    A further object, feature, or advantage of the present invention is to increase efficiency of an environmental chamber by placing less stress on the refrigeration system. 
         [0016]    A still further object, feature, or advantage of the present invention is to provide a light fixture which also aids in the performance of dimmable lighting, by providing more stability in terms of quality (such as less flickering) at settings near the lower end of the dimming range. 
         [0017]    Another object, feature, or advantage of the present invention is to provide a light fixture for use in an environmental chamber which does not require a refrigeration system to control the temperature within the light fixture. 
         [0018]    One or more of these and/or other objects, features, or advantages of the present invention will become apparent from the specification and claims that follow. 
         [0019]    According to one aspect of the present invention a light fixture includes a plurality of fluorescent bulbs wherein a light intensity of each of the plurality of fluorescent bulbs is related to operating temperature of the fluorescent bulbs, a sensor for sensing a physical parameter related to the light intensity, and a circuit adapted for monitoring the sensor and controlling the operating temperature of the fluorescent bulbs to maintain the operating temperature of the fluorescent bulbs within a range having a lower temperature and an upper temperature. 
         [0020]    According to another aspect of the present invention, a light fixture includes a plurality of fluorescent bulbs, a temperature sensor position proximate the plurality of fluorescent bulbs, a cooling device (such as a fan) for cooling the plurality of fluorescent bulbs, and an electrical circuit connected to the temperature sensor and cooling device, wherein the electrical circuit is adapted to maintain light intensity of the fluorescent bulbs within a predetermined range of optimal light output by controlling the cooling device to control the temperature of the fluorescent bulbs and to thereby increase the temperature of the plurality of fluorescent bulbs if the temperate of the fluorescent bulbs is below the predetermined range and to decrease the temperature of the fluorescent bulbs if the temperature is above the predetermined range. 
         [0021]    According to another aspect of the present invention an environmental chamber includes an insulated cabinet, a refrigeration system adapted for controlling the temperature within the insulated cabinet, a control system, and one or more light fixtures disposed within the insulated cabinet. Each light fixture includes a plurality of fluorescent bulbs, a sensor, and a thermal management control system electrically connected to the sensor and adapted to provide for heating and cooling of the plurality of fluorescent bulbs to maintain optimum light intensity of the fluorescent bulbs. 
         [0022]    According to another aspect of the present invention a method of maintaining light intensity of fluorescent bulbs in an environmental chamber is provided. The method includes monitoring a physical parameter associated with the light intensity of the fluorescent bulbs inside one or more light fixtures within an environmental chamber and based on the physical parameter, adjusting the temperature of the fluorescent bulbs to maintain an optimum light intensity of the fluorescent bulbs. 
         [0023]    According to another aspect of the present invention a method of maintaining light intensity of fluorescent bulbs in an environmental chamber includes providing an environmental chamber having an insulated cabinet, a refrigeration system adapted for controlling the temperature within the insulated cabinet, a control system, and one or more light fixtures disposed within the insulated cabinet. Each light fixture includes a plurality of fluorescent bulbs, a sensor, and a thermal management control system electrically connected to the sensor and adapted to provide for heating and cooling of the plurality of fluorescent bulbs to maintain optimum light intensity of the fluorescent bulbs. The method further includes monitoring a physical parameter associated with the light intensity of the fluorescent bulbs using the sensor, and based on the physical parameter adjusting the temperature of the fluorescent bulbs in the light fixture to maintain an optimum light intensity of the fluorescent bulbs in the environmental chamber. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]      FIG. 1  is a perspective view of one embodiment of an environmental chamber with a refrigeration system of the present invention. 
           [0025]      FIG. 2  is a cross sectional view of one embodiment of an environmental chamber of the present invention. 
           [0026]      FIG. 3  is a view of one embodiment of a light fixture of the present invention. 
           [0027]      FIG. 4  is a cross section of a front view of one embodiment of a light fixture of the present invention. 
           [0028]      FIG. 5  is a perspective view of one embodiment of a light fixture of the present invention. The light fixture barrier is not shown. 
           [0029]      FIG. 6  is an electrical schematic for one embodiment of a light fixture of the present invention. 
           [0030]      FIG. 7  is a view of one embodiment of a light fixture of the present invention. 
           [0031]      FIG. 8  is a graph showing the relationship between temperature of an environmental chamber and light intensity. 
           [0032]      FIG. 9  is a graph showing one embodiment of the temperature versus light intensity relationship for a particular lamp as supplied by the lamp manufacturer. 
           [0033]      FIG. 10  is a block diagram of another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0034]    The present invention relates to a light fixture and especially a light fixture for use in an environmental chamber. The light fixture is adapted to optimize light intensity (as may be measured in μmoles/m 2 /sec) and to provide a stable lamp output, including at ambient temperatures above and below an optimum point. Although specific embodiments are described herein, the present invention is not to be limited to the specific embodiments described. 
         [0035]      FIG. 1  illustrates one embodiment of an environmental chamber  10 . The environmental chamber  10  has an insulated cabinet  12 . Atop the insulated cabinet  12  is an ultrasonic humidifier  20 . Within the insulated cabinet are chambers or compartments such as an upper compartment  14  and a lower compartment  24 . A first door  16  provides access to compartments  14  and second door  18  provides access to additional compartments. Within the cabinet  12  is a light fixture  50 . Located on top of the light fixture  50  is a thermal management system which can include one or more air circulation fans  70  ( FIG. 2 ). At the bottom of the light fixture  50  is a thermal barrier such as a Plexiglas barrier  51 . 
         [0036]      FIG. 2  provides a cross sectional view of the environmental chamber of  FIG. 1 . The environmental chamber  10  shown in  FIG. 1  and  FIG. 2  is merely representative of numerous styles, types, varieties, sizes, and configurations of environmental chambers which provide the light fixture of the present invention. 
         [0037]      FIG. 3  illustrates one embodiment of a light fixture  50  of the present invention. The light fixture  50  has a frame  56  with opposite ends  52 ,  54  and a metal sheet  61  between the opposite ends  52 ,  54 . Slits or perforations  62  in sheet  61  are shown. In  FIG. 3 , a number of sockets  58  are shown with corresponding fluorescent bulbs  60 . A temperature sensor  64  which may be a part of a thermostat is shown. Preferably, the temperature sensor  64  is placed away from the air inlet and in a position which allows for a representative temperature to be measured, as it will be appreciated that there may be some variance of the temperature of each fluorescent bulb  60  due to its location. A light socket  66  is also shown with incandescent bulbs  68  on opposite ends of the light socket  66 . It should be appreciated that incandescent bulbs  68  are often used in environmental chambers to add more red, infrared spectrum, particularly where plants are being grown. The fluorescent bulbs shown are T5 compact fluorescent bulbs otherwise known as twin T5 bulbs. Such bulbs have significant reduction in efficiency once the ambient temperature drops below the optimum point. Of course, other types of bulbs may used such as T5 linear bulbs or different sizes of bulbs such as T8 bulbs. It should be appreciated, however, that bulbs such as T8 bulbs do not exhibit the same reduction in light output as the ambient temperature drops. Of the commercially available fluorescent bulbs, T5 fluorescents have the most significant reduction in light output once the ambient temperature drops below the optimum point. Due to the smaller size of a T5 fluorescent bulb in comparison to a normal T8 or T12 fluorescent bulb, a T5 fluorescent bulb does have some advantages. For example, a light fixture may provide for greater light intensity for a predetermined size given the small size of the florescent bulbs. It should be appreciated, however, that other sizes, types, and quantities of fluorescent bulbs may be used. T5 fluorescent bulbs also have a higher Lumens per Watt ratio than T8 or T12 fluorescent bulbs. 
         [0038]      FIG. 4  is a cross sectional view of one embodiment of a light fixture. Note there are vertical slots  74  and horizontal slots  76  to assist in air intake. Fans  70  are shown positioned over the slotted sheet metal plate  61 , to which the lamp holders  58 , fluorescent bulbs  60  and other light fixture electrical components are attached. According to one embodiment, if the temperature of the ambient air surrounding the fluorescent bulbs  60  drops below an optimal point or range, the fans  70  will de-energize. De-energizing the air circulation fans will keep the forced air exchange between the enclosed lamp space and the chamber environment to a minimum. Without a forced air exchange, the heat produced by the lamps and ballasts will no longer be removed from inside the lamp space, and will serve to heat the ambient air surrounding the fluorescent bulbs. If the temperature inside the light fixture rises above the optimal point or optimum range for maximum lamp efficiency, the air circulation fans  70  will energize, and produce a forced air exchange between the environment inside the chamber with the ambient air surrounding the bulbs inside the light fixture  50 . The resulting air exchange will cool the air surrounding the fluorescent bulbs inside the light fixture  50 . It should be observed that in the design shown, there will be some chamber air entering through the slots  74 ,  76  as air may be forced in by the environmental chamber&#39;s main air circulation fans (not shown). This small remaining air exchange will also include some convection, as the heat from the lamps  60  and ballasts will have a tendency to rise out of the axial fan holes. 
         [0039]      FIG. 5  is a perspective view of one embodiment of a light fixture  50  of the present invention. The frame or housing of the light fixture includes opposite sides  80 ,  84  and front side  82 . The inside of the frame or housing of the light fixture  50  may be a uniform white surface or clad with spectral aluminum to further enhance light irradiance of the fluorescent lamps. 
         [0040]      FIG. 6  is an electrical schematic of one embodiment of a light fixture according to the present invention. In  FIG. 6 , a thermostat  64  is shown which includes a temperature sensor and switch which form a part of the electrical circuit of  FIG. 6 . The thermostat  64  is set to turn a switch on to activate the fans  70  when the temperature exceeds a first set point and the thermostat  64  is set turn the switch off to deactivate the fans  70  when the temperature is less than a second set point. The first set point and the second set point are associated with a temperature range based around the optimal point corresponding with the highest light intensity for the fluorescent lights  60 . In the case of T5 compact fluorescent bulbs the optimal point is approximately 35° C. or within a range of approximately 34° C. to 36° C.  FIG. 9 . If the temperature of the ambient air surrounding the fluorescent bulbs drops below the optimal point or the optimal range, the fans will de-energize. Also ballasts  90  are required to energize the fluorescent lights  60  and may be electronic type. 
         [0041]      FIG. 7  is another view of one embodiment of a lamp layout inside a light fixture according to one embodiment of the present invention. 
         [0042]    Two plant growth chambers, one with the intensity maintaining light fixture and one with a conventional light fixture were compared. The plant growth chamber with the light fixture of the present invention is shown on the right. Note that the plant growth chamber on the right provides significant energy savings over the plant growth chamber on the left. The plant growth chamber on the right uses T5 lamps as opposed to T12 lamps as on the left which is a viable option because although the T5 lamps have varying light intensity based on temperature, the temperature of the T5 lamps is maintained to result in an optimum light intensity. One of the added advantages of a plant growth chamber having the light fixture of the present invention is that a smaller condensing unit can be used. Because there is less heat generated by the fluorescent lamps, there is less heat in the environmental chamber and the evaporator coils run warmer. Warmer evaporator coils are conducive to better overall chamber performance such as higher potential humidity levels, etc. Furthermore, because there is less heat to remove from the fluorescent lights, a smaller condensing unit can be used. Typically, the condensing unit is the component that consumes the most electrical power. Thus, the present invention provides for numerous advantages. 
         [0000]    
       
         
               
               
               
             
               
               
               
             
           
               
                   
                   
               
               
                   
                 PGC-10 MODEL 
                 PGC-10 MODEL 
               
               
                   
                 2006 
                 2007 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 LAMP TYPE 
                 F48T12/CW/VHO 
                 F54T5/841/HO 
               
               
                 LAMP WATTAGE 
                 110 W 
                 54 W 
               
               
                 DESIGN LUMENS PER LAMP 
                 4950 
                 4750 
               
               
                 NUMBER OF LAMPS PER CHAMBER 
                 16 
                 18 
               
               
                 TOTAL LUMENS PER CHAMBER 
                 79200 
                 85500 
               
               
                 LIGHT OUTPUT @ 6″ FROM LAMPS 
                 1000 μmoles/m 2 /sec 
                 1075 μmoles/m 2 /sec 
               
               
                 HEAT GENERATED BY FLUOR. LAMPS 
                 5984 BTU/hr 
                 3304 BTU/hr 
               
               
                 HEAT GENERATED BY INC. LAMPS 
                 680 BTU/hr or 100 W 
                 340 BTU/hr or 100 W 
               
               
                 HEAT GENERATED BY ALL LAMPS 
                 6664 BTU/hr 
                 3644 BTU/hr 
               
               
                 FLUORESCENTS KW CONSUMPTION 
                 2112 Watts 
                 1112 Watts 
               
               
                 INCANDESCENS KW CONSUMPTION 
                 200 Watts 
                 100 Watts 
               
               
                 LIGHTING KW CONSUMPTION 
                 2312 Watts 
                 1212 Watts 
               
               
                 CONDENSING UNIT SIZE 
                 1½ HP 
                 ¾ HP 
               
               
                 CONDENSING UNIT MODEL 
                 F3AH-A150-TFC 
                 FTAH-A074-IAV 
               
               
                 AMPERAGE DRAW W/LIGHTS ON 
                 15 
                 9 
               
               
                 AMPERAGE DRAW W/LIGHTS OFF 
                 12 
                 6 
               
               
                 KW CONSUMPTION W/LIGHTS ON 
                 5.4 
                 3.4 
               
               
                 KW CONSUMPTION W/LIGHTS OFF 
                 4.2 
                 2.2 
               
               
                 COST PER Kw/hr OF ELECTRICITY 
                 $0.100 
                 $0.100 
               
               
                 DAILY CHAMBER OPERATING COST 
                 $11.76 
                 $6.96 
               
               
                 YEARLY CHAMBER ELECTRICAL 
                 $4,292.40 
                 $2,540.40 
               
               
                 OPERATING $ 
               
               
                   
               
             
          
         
       
     
         [0043]      FIG. 8  provides a graph illustrating the effect of ambient temperature and light intensity. Data regarding the effect of ambient temperature on light intensity may also be obtained from manufacturers of fluorescent bulbs  FIG. 9 . It should further be appreciated that light intensity may be considered to be synonymous with light irradiance and light output. Light intensity, output, irradiance is measured in μmoles/m 2 /sec, Lumens, Watts/m 2 , lux, foot candles, or μeinsteins/m 2 /sec. 
         [0044]    Although the present invention has been described with respect to a preferred embodiment, the present invention contemplates numerous variations, options, and alternatives. For example, although one or more fans and a thermostat may be used as the thermal management system as shown in  FIG. 6 , the thermal management system may otherwise be implemented. If, for example, an environmental chamber is likely to be used at cool temperatures, then in addition to a fan a heater may be used to provide additional heat to the fluorescent bulbs such that they maintain optimum light intensity. In operation, the heater may turn on in advance of the fluorescent bulbs so that the temperature is such that optimum light intensity may be achieved when the fluorescent bulbs turn on. Other types of thermal management may also be performed including liquid heating or cooling instead of air heating or cooling. Where fans are used, the present invention contemplates that instead of turning fans on and off, a variable speed fan can be used to assist in maintaining conditions for optimum light intensity. 
         [0045]    By way of another example, instead of using a temperature sensor or thermostat, light intensity may be measured with a photometer. Where light intensity is less than optimum, then temperature may be increased or decreased accordingly. Another example of a physical parameter that may be measured to provide insight into light intensity or temperature is the current draw of the fluorescent bulbs over time. 
         [0046]    It should also be appreciated that where a temperature sensor is used, the temperature sensor need not be proximate the fluorescent bulbs if light intensity can otherwise be inferred. For example, the temperature within the environmental chamber may be related to the light intensity. 
         [0047]      FIG. 10  illustrates a block diagram of another embodiment of the present invention. In  FIG. 10 , a thermal management control system  120  is shown. A sensor  122  is electrically connected to the thermal management control system  120 . The sensor  122  may be a temperature sensor near fluorescent bulbs, or a temperature within an environmental chamber. The sensor  122  may also be a photometer, a current sensor or other type of sensor. One or more cooling devices  124  are operatively connected to the thermal management control system  120 . The cooling device  124  may include one or more fans, one or more variable speed fans, or provide for liquid cooling. A heating device  126  may also be operatively connected to the thermal management control system  120 . The heating device  126  may include a heater. 
         [0048]    It should be appreciated that more than one sensor may be used at a time. For example, both a temperature sensor and a light sensor may be used together. A determination of whether the light fixture is operating in an optimum range can be made with a light sensor. Then a temperature sensor can indicate whether heat should be added or removed to stay in or return to the optimum range. Where a light sensor is used, it may be placed approximately six inches from the light fixture barrier, pointing towards the fluorescent bulbs. 
         [0049]    A relationship between current draw and light intensity may be inferred. Where such a relationship is known, measuring current draw, such as with a current sensor, may be used to assist in determining light intensity. 
         [0050]    The present invention is not to be limited to the specific embodiments described herein but also other variations, options, and alternatives within the spirit and scope of the invention.