Patent Publication Number: US-9418829-B2

Title: Low pressure lamp using non-mercury materials

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 14/536,380, filed Nov. 7, 2014, which is a continuation of U.S. application Ser. No. 14/273,286, filed May 8, 2014, which is a continuation of U.S. application Ser. No. 13/631,311, filed Sep. 28, 2012, all of which are incorporated herein by reference in their entireties. 
    
    
     BACKGROUND 
     The present application relates generally to the field of low-pressure arc discharge lamps. The present application relates more specifically to the field of mercury-free low-pressure arc discharge lamps. 
     Low-pressure arc discharge lamps, for example fluorescent lamps, are more efficient at generating lumens per watt than incandescent bulbs. However, mercury or a mercury amalgam is conventionally used as an emissive material because mercury emits mostly ultraviolet photons and because mercury has a high vapor pressure, making mercury easy to vaporize. However, because of the potentially toxic effects of mercury when it is released into the environment, there is a need for an improved mercury-free lamp. 
     SUMMARY 
     One embodiment relates to a mercury-free low-pressure arc discharge lamp having a bulb. The bulb includes a non-mercury emissive material. When the bulb is in a non-operational state, the emissive material condenses into a liquid or solid, and when the bulb is in an operational state the emissive material forms an emitter, the emitter in combination with one or more gases generate photons when excited by an electrical discharge. 
     Another embodiment relates to a method of operating a mercury-free low-pressure lamp. The method includes providing a bulb having an envelope filled with one or more gases at a low pressure, and a non-mercury emissive material. The method further includes vaporizing at least a portion of the emissive material into the envelope to form an emitter, exciting the emitter with an electron such that the emitter in combination with the gases generate visible or ultraviolet photons. 
     Another embodiment relates to an apparatus for operating a mercury-free low-pressure lamp including a bulb having: one or more phosphors configured to convert photons to visible or other visible wavelengths, an envelope filled with one or more gases at a pressure below 0.01 atmospheres, and at least one emissive material including at least one of an alkali metal and an alkaline earth metal. The apparatus includes a circuit configured, in response to a startup command, to cause the emissive material to vaporize into the envelope to form an emitter and to cause the excitation of the emitter with an electron such that the emitter in combination with the gases generate visible or ultraviolet photons. 
     Another embodiment relates to a method of starting a low-pressure lamp. The method includes providing a bulb having an envelope filled with one or more gases at a pressure below 0.01 atmospheres. The method further includes spraying at least one non-mercury emissive material into the envelope and exciting the emissive material with an electron such that the emissive material in combination with the gases generate visible or ultraviolet photons. 
     The foregoing is a summary and thus by necessity contains simplifications, generalizations and omissions of detail. Consequently, those skilled in the art will appreciate that the summary is illustrative only and is not intended to be in any way limiting. Other aspects, inventive features, and advantages of the devices and/or processes described herein, as defined solely by the claims, will become apparent in the detailed description set forth herein and taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a schematic diagram of a lamp, shown according to an exemplary embodiment. 
         FIG. 1B  is a schematic diagram of a portion of the lamp of  FIG. 1A , shown according to an exemplary embodiment. 
         FIG. 2A  is a schematic diagram of a lamp, shown according to another embodiment. 
         FIG. 2B  is a schematic diagram of a lamp, shown according to another embodiment. 
         FIG. 3  is a schematic diagram of a portion of a lamp, shown according to another embodiment. 
         FIG. 4  is a schematic diagram of a portion of a lamp, shown according to another embodiment. 
         FIG. 5  is a schematic diagram of a portion of a lamp, shown according to another embodiment. 
         FIG. 6  is a schematic diagram of a portion of a lamp, shown according to another embodiment. 
         FIG. 7  is a schematic diagram of a portion of a lamp, shown according to another embodiment. 
         FIG. 8  is a schematic diagram of a plurality of the lamps of  FIG. 7  coupled to an electrical system, shown according to an exemplary embodiment. 
         FIG. 9  is a schematic diagram of a portion of a lamp, shown according to another embodiment. 
         FIG. 10  is a detailed block diagram of the processing electronics of  FIG. 9 , shown according to an exemplary embodiment. 
         FIG. 11  is a schematic diagram of a portion of a lamp, shown according to another embodiment. 
         FIG. 12  is a flowchart of a process of operating a lamp, shown according to an exemplary embodiment. 
         FIG. 13  is a flowchart of a process of operating a lamp, shown according to another embodiment. 
         FIG. 14  is a flowchart of a process of operating a lamp, shown according to another embodiment. 
         FIG. 15  is a flowchart of a process of operating a lamp, shown according to another embodiment. 
         FIG. 16  is a flowchart of a process of operating a lamp, shown according to another embodiment. 
         FIG. 17  is a flowchart of a process of operating a lamp, shown according to another embodiment. 
         FIG. 18  is a schematic diagram of a portion of a lamp, shown according to another embodiment. 
         FIG. 19  is a schematic diagram of a portion of a lamp, shown according to another embodiment. 
         FIG. 20  is a schematic diagram of a portion of a lamp, shown according to another embodiment. 
         FIG. 21  is a flowchart of a process of starting a lamp, shown according to an exemplary embodiment. 
         FIG. 22  is a flowchart of a process of starting a lamp, shown according to another embodiment. 
         FIG. 23  is a schematic diagram of a lamp, shown according to another embodiment. 
         FIG. 24  is a schematic diagram of a lamp, shown according to another embodiment. 
         FIG. 25  is a schematic diagram of a lamp, shown according to another embodiment. 
         FIG. 26  is a schematic diagram of a lamp, shown according to another embodiment. 
         FIG. 27  is a schematic diagram of a lamp, shown according to another embodiment. 
         FIG. 28  is a schematic diagram of a lamp, shown according to another embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Referring generally to the Figures, a lamp and components thereof are shown according to exemplary embodiments. The lamp may be a low-pressure arc discharge lamp, for example a fluorescent lamp, and may range in size from a compact fluorescent lamp (CFL) to a high-output parking lot or stadium sized lamp. The lamp includes a bulb, which may have an end plug and may be supported by a fixture. The bulb includes an envelope configured to receive and contain an ionizable gas. The lamp may be an electrodeless lamp or may include electrodes configured to create an arc which ionizes said gas. An emissive material is vaporized and dispersed in the envelope to form one or more emitters (i.e., atoms of the vaporized emissive material), which are excited by free electrons. An excited emitter gives off a photon as an electron in the emitter returns to a lower energy state from an excited, higher energy state. The photon given off by the emitter is converted by phosphors in the bulb from an invisible or less desirable wavelength to a visible or more desirable wavelength. 
     Conventionally, mercury or a mercury amalgam is used as an emissive material because mercury vapor emits mostly ultraviolet photons and because mercury has a high vapor pressure, making mercury easy to vaporize into the envelope. Mercury&#39;s vapor pressure is sufficiently high that the heat from ionizing the inert gas causes the mercury to vaporize. 
     Non-mercury emissive materials tend to have lower vapor pressures than mercury and, thus, may need assistance in order vaporize, especially in the short time spans that users expect a lamp to start and reach peak lumen output. According to one embodiment, a heater is used to vaporize the emissive material. According to another embodiment, a cooler is used to condense the emissive material in a selected portion of the lamp, for example, proximate the heater. According to various embodiments, the lamp may include a circuit configured to control the activation and deactivation of the heater and cooler. According to yet other embodiments, an injector may be used to spray the emissive material into the envelope. As the systems and methods described herein may require additional power during startup, systems and methods for controlling the startup of a plurality of lamps to reduce current or power spikes are also described. 
     Before discussing further details of the lamps and/or the components thereof, it should be noted that for purposes of this disclosure, the term coupled means the joining of two members directly or indirectly to one another. Such joining may be stationary in nature or moveable in nature and/or such joining may allow for the flow of fluids, electricity, electrical signals, or other types of signals or communication between the two members. Such joining may be achieved with the two members or the two members and any additional intermediate members being integrally formed as a single unitary body with one another or with the two members or the two members and any additional intermediate members being attached to one another. Such joining may be permanent in nature or alternatively may be removable or releasable in nature. 
     Referring to  FIGS. 1A and 1B , a lamp  100  (e.g., low-pressure lamp, a low-pressure arc discharge lamp, fluorescent lamp, etc.) is shown according to an exemplary embodiment. The lamp  100  includes a bulb  101  (e.g., tube, housing, luminary, etc.), which includes an envelope  102  (e.g., tube, container, etc.) and an emissive material  120 . An inert gas  108  (e.g., noble gas, neon, argon, krypton, xenon, etc.) is sealed inside the envelope  102  during manufacture of the bulb  101 . The envelope  102  is sealed such that the inert gas  108  is maintained at a low pressure (e.g., less that 1% of atmospheric pressure, approximately 0.3% of atmospheric pressure, etc.). Other gases may be used; however, using noble gases (e.g., inert gases) simplifies the chemistry of ionization and eliminates the need for energy that would otherwise be required to split a molecule during ionization. 
     As shown, the envelope  102  is lined with one or more phosphors  104  that are configured to receive photons of visible and invisible (e.g., ultraviolet light) light and emit photons of visible light. For example, the phosphors  104  may be configured to convert photons from one wavelength to another visible wavelength. Further, the phosphors may be configured to provide specific wavelengths, for example to provide a desired color, or a plurality of visible wavelengths in order to produce a whiter light. 
     Referring to  FIG. 2A , it is contemplated that in some embodiments, the bulb  101  may not include any phosphors, for example, in a germicidal lamp in which ultraviolet wavelengths are preferred. Referring to  FIG. 2B , it is further contemplated that the bulb  201  may include more than one layer of phosphors, shown as first layer of phosphor  204   a  and second layer of phosphor  204   b.  Having multiple layers of phosphor may facilitate sequential deposition of phosphors having different wavelength conversion properties. Having multiple layers may also enable the use of one or more intermediate phosphors which convert the plasma radiation wavelengths to an intermediate wavelength, which in turn is converted to an output wavelength by an outer layer of phosphors. 
     Referring to  FIG. 2B , the bulb  201 ′ may include a first or inner envelope  202 ′ configured to contain the emissive material  220 , the inert gas  208 , and the arc-discharge. The bulb  201 ′ may further include a second or outer envelope  203  (e.g., tube, housing, container, etc.) configured to support the phosphors  204 . According to the embodiment shown, the first envelope  202 ′ extends within the second envelope  203 . According to another embodiment, the first envelope  202 ′ may be adjacent to the second envelope  203 . The inner envelope  202 ′ maintains a relatively high temperature, for example, with respect to the outer envelope  203 . The space between the inner envelope  202 ′ and the outer envelope  203  may be substantially evacuated, filled with an inert gas, incorporate baffles, or be filled with a substantially transparent and/or translucent material (e.g., aerogel) to control convective heat transfer from the inner envelope  202 ′ to the outer envelope  203 . 
     Returning to  FIGS. 1A and 1B , the bulb  101  and envelope  102  may be formed of a material that is substantially translucent or substantially transparent to visible light, for example, glass, quartz, ceramic, etc. The envelope  102  is shown to be an elongated tube supported at opposite ends by one or more fixtures  106 . According to other embodiments, the bulb  101  and the envelope  102  may be bent in a circular shape, a U-shape, a spiral shape, or any other shape. The bulb  101  or envelope  102  may also take a form other than a simple tube, such as two or more tubes joined together. Depending on the shape of the bulb  101 , both ends of the bulb  101  may be supported by a single fixture  106 . According to various embodiments, the fixture  106  may be portable (e.g., a flashlight, torch, table lamp, etc.) or the fixture may be substantially stationary (e.g., a chandelier, a sconce, a streetlamp, etc.). According to some embodiments, the fixture  106  may be a part of the lamp  100 , and the bulb  101  may be releasably coupled to the fixture  106 . 
     Electrodes  110 , shown as first electrode  110   a  and second electrode  110   b,  create an arc that ionizes a portion of the inert gas  108  into ions  108 ′ and electrons  112 . The power or energy used to create the arc is received from one or more contacts  114 , which are shown as pins or bayonets. According to other embodiments, the contacts  114  may be prongs, flexible leads, screw-type contacts, or any other suitable electrical connector. The fixture  106  is configured to provide electrical power to contacts  114 . 
     Electrical power flowing to the lamp passes through a ballast  115 . As shown, the ballast  115  is located in the fixture  106 . According to another embodiment, the ballast  115  may be attached directly to the bulb  101 , for example, located in an end plug  116  between the contacts  114  and the electrode  110 . 
     In traditional fluorescent lamp installations, the ballast  115  comprises a simple inductor or resistor, and performs the single function of limiting the alternating current flowing through the lamp. A starter switch (not shown) may be included in series between the electrodes  110   a,    110   b,  and open in phase with the ballast to send an inductive voltage spike between the electrodes  110   a,    110   b  to create the arc and start the bulb  101 . However, more generally, the ballast may contain passive or active electrical components (e.g., transformer, autotransformer, solid-state inverter circuit) to convert the input voltage, frequency, and waveform to a different voltage, frequency, or waveform which is applied to the lamp electrodes  110 . For example, the ballast  115  may be configured to heat the electrodes  110   a,    110   b  to create a glow discharge which propagates through the bulb  101  to initiate the arc discharge and start the bulb  101 . Briefly referring to  FIGS. 2A and 2B , in some embodiments the electrodes  210  may each only have a single contact  214 . In these embodiments, the ballast  215  simply creates a high enough voltage between the electrodes  210   a,    210   b  that the gas in the envelope  202 ,  202 ′ breaks down and an arc discharges therebetween. In other embodiments, the ballast may convert the supplied power into radiofrequency (RF) power which is coupled into the plasma via capacitive, inductive, or RF absorption processes; in such embodiments electrodes  110  may take the form of capacitive plates, one or more inductive coils, or one or more RF antennas. In such embodiments electrodes  110  may be located entirely external to envelope  202 . 
     The switch  118  may be provided to switch or “turn” the lamp  100  on and off. The switch may be a manually operated switch or a remote control switch (e.g., operated by a computer system, an automatic controller, etc.), and the switch may be located on the lamp  100 , proximate the lamp  100 , or remote from the lamp  100 . According to the exemplary embodiment shown, the lamp  100  or a control circuit configured to start the lamp  100  is configured to receive a startup command, for example, from the switch  118  or a computer system. The control circuit may be configured to recognize a change in a power state as a startup command. The lamp  100  or a control circuit configured (e.g., the control circuit configured to start the lamp  100 , a control circuit configured to shut down the lamp  100 , etc.) may be configured to receive a shutdown command, for example, from the switch  118  or a remote controller. A remote control switch may be configured to operate in response to a signal (e.g., ultrasonic, RF, infrared, digital network, etc.) from a remote controller. 
     When the bulb  101  is in a non-operational state, as shown, for example, in  FIG. 1A , the emissive material  120  is largely in, or may condense into, a liquid or solid state. When the bulb  101  is in an operational state, as shown, for example, in  FIG. 1B , the condensed emissive material  120  is converted to emitters  120 ′. In some embodiments, this conversion may be a simple state change (i.e., evaporation) of an elemental emissive material  120 . In some embodiments, the emissive material  120  may be a mixture or amalgam of two or more materials, one or more of which may be evaporated to form emitters  120 ′. In some embodiments, the emissive material  120  may be a chemical compound which is thermally dissociated into emitters  120 ′ and non-emitting atoms or molecules. In some embodiments, the conversion may be facilitated by mechanical dispersion (e.g., spraying, injection, etc.) of the emissive material  120  within the envelope  102 . One or more free electrons  112  excite the emitter  120 ′, causing the emitter to emit or release a photon  122 , which may be of a visible or invisible wavelength (e.g., ultraviolet). The photon  122 , in turn, excites one of the phosphors  104 , which emits a photon  124  having a wavelength in the visible spectrum. 
     According to various exemplary embodiments, the emissive material  120  includes an alkali metal (e.g., lithium, sodium, potassium, rubidium, etc.). According to various embodiments, the emissive material  120  may be a mixture or alloy of atoms. According to one exemplary embodiment, the emissive material is sodium-potassium (NaK). According to another exemplary embodiment, the emissive material  120  is disodium-potassium (Na 2 K). According to various other embodiments, the emissive material  120  includes an alkaline earth metal (e.g., beryllium, magnesium, calcium, strontium, etc.). Non-mercury emissive materials tend to have lower vapor pressures than mercury and, thus, may need assistance in order to vaporize sufficiently. Systems and methods for dispersing non-mercury emissive materials  120  into the envelope  102  are described below. These systems and methods may also be used for dispersing mercury into the envelope. 
     Referring to a  FIG. 3 , a lamp  300  is shown according to an exemplary embodiment. The lamp  300  includes an envelope  302  lined with a layer of phosphors  304 . Electrodes  310  are configured to receive power from contacts  314  and to create an arc which ionizes the inert gas  312 . The lamp  300  is further shown to include a reservoir  350  and a thermal controller, which may include a heater  330  and/or a cooler  340 . 
     The heater  330  is configured to provide energy (e.g., heat, etc.) to the emissive material  320 . According to the embodiment shown, the heater  330  is configured to raise the temperature of the emissive material  320  in the reservoir  350  such that the vapor pressure of the emissive material  320  is increased such that the emissive material  320  begins to vaporize. For example, the heater  330  may be configured to raise the vapor pressure of the emissive material  320  above the pressure inside the envelope  302 . According to various embodiments, the heater  330  is configured to raise the temperature of the first portion of the lamp above 50 degrees centigrade and is configured to at least partially vaporize the emissive material  320  within a startup time of the heater  330  receiving power. According to another embodiment, the heater  330  is configured to completely vaporize the emissive material  320  within a startup time of the heater  330  receiving power. The startup time may be sufficiently short such that there is no perceptible delay (e.g., less than 1 second, less than 0.5 seconds, less than 0.3 seconds) in starting the lamp  300 . According to one embodiment, the startup time may be less than 5 seconds. The startup time of the apparatuses, systems, and methods described herein may be substantially faster than the startup times of conventional sodium vapor lamps, which may take 30 seconds to start to arc. According to other embodiments, the heater  330  may be configured to raise the vapor pressure of the emissive material  320  above a threshold pressure for maintaining a discharge, and the heater  330  may be configured to attain the threshold pressure within a startup time of the heater  330  receiving power. According to another embodiment, the heater  330  is configured to raise the temperature of the emissive material  320  to at least the boiling point of the emissive material. The heater  330  may be configured to heat the emissive material using a resistive element, electromagnetic induction, electromagnetic radiation (e.g., radio frequency, microwaves, millimeter, infrared, visible light, etc.), ultrasound, or resistive self-heating. As shown in  FIG. 3 , the heater  330  is coupled to or is incorporated into the lamp  300 , for example, in the bulb  301 , and more specifically in the end plug  316 . According to various embodiments, the heater may be located in a position other than the end plug. For example, referring briefly to  FIG. 2B , the heater  230  may be coupled to or incorporated into the envelope  203 ; or, referring briefly to  FIG. 4 , the heater  430  may be coupled to or be incorporated into the fixture  416  that supports the lamp  400 . 
     The lamp  300  is further shown to include a control circuit  360 . The control circuit  360  may include any number of mechanical or electrical circuitry components or modules for controlling the heater  330  or the cooler  340 . For example, the control circuit  360  may include a switch, a capacitor, an inductor, a resistor, or other solid state circuitry components. According to another embodiment, the control circuit  360  may include a processor. The processor may be or include one or more microprocessors, an application specific integrated circuit (ASIC), a circuit containing one or more processing components, a group of distributed processing components, circuitry for supporting a microprocessor, or other hardware configured for processing. According to an exemplary embodiment, the processor is configured to execute computer code stored in a memory to complete and facilitate the activities described herein. The memory can be any volatile or non-volatile memory device capable of storing data or computer code relating to the activities described herein. For example, the memory may include modules that are computer code modules (e.g., executable code, object code, source code, script code, machine code, etc.) configured for execution by the processor. When the code modules are executed by the processor, the control circuit is configured to complete the activities described herein. 
     The control circuit  360  may be configured to control the heater  330  in response to an input. For example, the control circuit  360  may be configured to switch off the heater  330  in response to an input. According to one embodiment, the control circuit  360  controls the heater  330  in response to a profile in time. For example, the circuit  360  may include a timer circuit which switches off the heater  330  a fixed amount of time after power is applied to the lamp  300 . According to another embodiment, the control circuit  360  switches off the heater  330  in response to an electrical state or property of the lamp  300 . For example, the circuit  360  may detect a voltage or a current, or the circuit  360  may detect that a shutdown command. The circuit  360  may detect whether electrode  310  has established an arc and has ionized the inert gas  312 . 
     As shown, the lamp  300  includes a sensor  362  which may receive the input and provide the input to the control circuit  360 . The sensor  362  is illustrated as separate from the control circuit  360 , but in other embodiments, the sensor  362  may be part of the control circuit  360 . According to one embodiment, the control circuit  360  switches off the heater  330  in response to a temperature of the lamp  300  or a portion thereof, for example, the bulb  301 , the envelope  302 , the inert gas  312 , or a portion of the end plug  316 . For example, the sensor  362  may include a thermostat, a thermistor, a thermocouple, etc., and the circuit  360  may use the sensor  362  to detect the temperature of the lamp  300  or a portion thereof. According to another embodiment, the control circuit  360  switches off the heater in response to an optical output of the bulb  301 . According to various embodiments, the optical output of the bulb  301  may be a total output, a brightness at a first location, an irradiance, or a spectral irradiance. For example, the sensor  362  may include a photodiode, phototransistor, or other light-sensitive device, and the circuit  360  may use the sensor to detect the light output of the bulb  301 . 
     When the lamp  300 ,  400  is switched off and allowed to cool, the emissive material  320 ,  420  may condense, returning to a liquid or solid state. That is, the emitter may form (e.g., transform into, become, condense into, etc.) a liquid or sold state of the emissive material  320 . Condensation generally occurs at the coolest part of the lamp  300 ,  400 . As shown in  FIG. 4 , the emissive material  420  condenses along the envelope  402 . Accordingly, the heater  430  may be configured to heat at least a portion of the envelope  402  in order to vaporize the emissive material  420 . According to one embodiment, the heater  430  is configured to heat the entire envelope  402 . 
     Returning to  FIG. 3 , the lamp  300  is configured such that the emissive material  320  preferably condenses in the reservoir  350 . That is, the reservoir  350  is configured to induce condensation of the emissive material  320  therein. Accordingly, the heater  330  can focus the heating energy on a more concentrated portion of the lamp, thereby reducing the energy required and the time necessary to vaporize the emissive material  320 . The reservoir  350  may be of any suitable shape, for example, the reservoir  350  may be a recess, a depression, or a substantially flat surface. The reservoirs  350  are illustrated as being located on the end plug  316  outboard of the electrodes  310 . According to other exemplary embodiments, the reservoirs  350  may be located elsewhere on the lamp  300 , for example, along the envelope  302 . According to another exemplary embodiment, the reservoir  350  may be located substantially between the electrodes  310  and thus able to take advantage of the electricity and heat of the electrodes  310  to vaporize the emissive material  320  during startup. 
     As shown, the reservoir  350  is configured to receive the emissive material  320 , and the heater  330  is configured to heat at least one of the reservoirs  350  and the emissive material  320  therein. Referring to  FIG. 5 , the lamp may include a plurality of reservoirs  550 , shown as first through fourth reservoirs  550   a - 550   d,  and the heater  530  may be configured to heat the emissive material  520  in the reservoirs  550  sequentially, simultaneously, or any combination thereof. Heating the reservoirs sequentially reduces the peak energy (e.g., current draw) required to vaporize the emissive material  520 ; whereas, heating the reservoirs simultaneously may help the lamp achieve peak lumen output in a shorter period of time. 
     The cooler is configured to remove energy from the emissive material  320 . The cooler  340  is configured to reduce the temperature of at least a portion of the lamp  300  (e.g., a cold spot, etc.) such that the emissive material  320  preferentially condenses at the cold spot. For example, the cooler  340  may be used to induce condensation of the emissive material  320  in the reservoir  350 . The portion cooled by the cooler  340  may be the same portion or approximately the same portion (i.e., proximate to) the portion of the lamp heated by the heater  330 . Accordingly, the cooler  340  induces condensation of the emissive material  320  proximate the heater  330 , thereby preparing the lamp  300  to more efficiently startup in response to the next startup command. According to another embodiment, the cooler induce condensation of the emissive material at a portion of the lamp  300  remote from the reservoir  350 . The lamp may then be configured such that the emissive material  320  that is in a liquid state at the cold spot flows to the reservoir  350 . 
     According to one embodiment, the cooler  340  reduces the temperature of the cold spot via passive cooling. For example, the cooler  340  may cool by radiating heat to the environment, by convecting heat to the environment, or by conducting heat to another location (e.g., another portion of the lamp, to the environment, etc.). As shown, the cooler  340  includes a fin  342  which is configured to increase the heat flux from the reservoir  350  to the environment around the lamp  300 . According to one embodiment, the cooler  340  may include a heat pipe. 
     According to another embodiment the cooler  340  reduces the temperature of the cold spot via active cooling. For example, the cooler  340  may cool by forcing a fluid (e.g., air, a liquid, etc.) over the cold spot or by forcing a fluid over another portion thermally coupled to the cold spot. The cooler  340  may be powered by a power supply external to the lamp  300 . For example, the cooler may be coupled to mains electricity and may be configured to receive power even when the lamp is switched off. For example, the control circuit  360  may be configured to provide power to the cooler even after power is removed from electrode  310  and the bulb  301  is in a non-operational state. 
     The cooler may be powered by an energy storage device (e.g., power source, etc.) coupled to the lamp. Referring briefly to  FIG. 11 , the energy storage device  1168  may be located in a fixture  1106  configured to support the bulb  1101 . Referring to  FIG. 6 , the energy storage device  668  may be located in the end plug  616  of the lamp  600 . According to various embodiments, the energy storage device  668  may be a battery or a capacitor. The energy storage device  668  may be charged while the lamp  600  is switched on. For example, the energy storage device  668  may be charged by a thermoelectric generator  664  which generates energy from heat from the bulb  601 . The energy storage device  668  may be charged by a photovoltaic cell  662  (e.g., solar cell) which generates energy from the light from the bulb  601 . The energy storage device  668  may be charged be electricity from a power supply external to the lamp  600 . For example, the energy storage device may be coupled to mains electricity through pins  614 . 
     Referring to the embodiments of  FIGS. 27 and 28 , shown schematically, in some embodiments, the reservoir may have the form of a pattern or network distributed over a portion of the inner surface of the envelope. According to some embodiments, at least a portion of the pattern or network includes microchannels etched or printed onto the inner surface of the envelope  2702 ,  2802  of the bulb  2701 ,  2702 . According to other embodiments, at least a portion of the pattern or network includes a material (e.g., a wick, a tapered-pitch fabric wick, etc.) wetted by the emissive material, such that the condensing emissive material will be distributed over the pattern by capillary force. The pattern or network may comprise a resistive heater. The pattern or network may comprise paths which act as resistive self-heaters when coated with emissive material. 
     As shown in  FIG. 27 , the lamp  2700  includes a first conductor  2790  extending from the first electrode  2710   a,  and a second conductor  2792  extending from the second electrode  2710   b.  At least one path  2794  (e.g., channels, filaments, etc.) extends between the first and second conductors  2790 ,  2792 , forming a portion of a current path between the electrodes  2710   a,    2710   b.  The paths  2794  are configured to preferentially induce condensation of the emissive material therein or thereon. For example, the paths  2794  may include a chrome filament, the paths  2794  may be passively cooled (e.g., coupled to a radiative element), or the paths  2794  may be actively cooled. Accordingly, when the lamp  2700  is in a non-operational state, the emissive material condenses into or onto the paths  2794 . During startup, current passes between the first conductor  2790  and the second conductor  2792  via the paths  2794 , the current passing through the emissive material and causing vaporization thereof. 
     As shown in  FIG. 28 , the first and second conductors  2892  may form more intricate networks where some portions of the conductors  2890 ,  2892  or paths  2894  have different cross-sections of their lengths. For example the networks may have the appearance of filigree or an arterial tree. In such an embodiment, the paths  2894  extend between the first and second conductors  2890 ,  2892  like capillaries. According to another embodiment, the elements  2890 ,  2892  are not conductors, instead being thickening channels such that as the emissive material condenses proximate the paths  2894 , the condensed material flows away from the paths  2894 . The emissive material may itself be the conductor, forming at least part of the conductive path. 
     Referring to the embodiments of  FIGS. 23-26 , shown schematically, it is contemplated that the components of the lamp  2300 ,  2400 ,  2500 ,  2600  may be assembled in a variety of different configurations. For example, the lamp  2300  includes a bulb  2301  supported by a fixture  2306 . The thermal controller  2331 , which is shown to include the heater  2330  and cooler  2340 , is located in the bulb  2301  along with the control circuit  2360 . For example, the thermal controller  2331  and the control circuit  2360  may be located between a plurality of envelopes. 
     Lamp  2400  includes a bulb  2401  having an end plug  2416 , the bulb  2401  supported by the fixture  2406 . The reservoir  2450  is located in the envelope  2402 , which is located in the bulb  2401 . The thermal controller  2431 , shown to include the heater  2430  and cooler  2440  are located in the end plug  2416 , along with the sensor  2462 , control circuit  2460  and energy storage device  2468 . In such an embodiment, a bulb  2401  having the improvements described herein may be installed (e.g., coupled, releasably coupled, etc.) into an existing fixture  2406 . 
     Lamp  2500  includes a bulb  2501  having an end plug  2516  supported by a fixture  2506 . The reservoir  2550  and envelope  2502  are located in the bulb  2501 . The heater  2530 , the cooler  2540 , and the sensor  2562  are located in the end plug  2516 . The control circuit  2560  and the energy storage device  2568  are located in the fixture  2506 . 
     Lamp  2600  includes a bulb  2601  having an end plug  2616  supported by a fixture  2606 . The reservoir  2650  is located in the bulb  2601 . The sensor  2662  is located in the end plug  2616 . The heater  2630 , the cooler  2640 , the control circuit  2660 , and the energy storage device  2668  are located in the fixture  2606 . The heater  2630  and the cooler  2640  are thermally coupled to the reservoir  2650 , for example, by a thermally conductive pathway  2633 . In such an embodiment, the more costly and durable components may be located in the fixture  2606 , thereby keeping down the per piece cost of the replaceable bulb  2601 . 
     Other embodiments not shown are further contemplated. For example, the heater and the cooler need not be in the same component, that is the heater may be in the bulb while the cooler is in the end plug, the heater may be in the end plug while the cooler is in the fixture, etc. Similarly, the control circuit and the energy storage device need not be in the same component, for example, the control circuit may be in the bulb while the energy storage device is in the end plug or fixture, the control circuit could be in the fixture while the energy storage device is in the end plug, etc. 
     When starting the lamps described herein, the lamp must vaporize on the order of several to tens of milligrams of the emissive material. Further, in a configuration in which the heater heats the entire envelope, on the order of dozens of grams of the lamp are also heated (e.g., inert gases, phosphors, etc.). The heat capacities involved may be on the order of 100 J/g to raise the temperatures from room temperature (approximately 25° C.) to a few hundred degrees Celsius. Thus, a single kilojoule may be sufficient to vaporize the emissive material during startup. However, due to the short period of time of startup, this may result in a temporarily high power draw on the electrical system that provides power to the lamp. Further, if a plurality of lamps are commanded on (e.g., switched on) substantially simultaneously, the power draw on the electrical system is multiplied. Accordingly, a startup system may be used to control the startup of the lamps to limit the overall power draw on the electrical system. According to one embodiment, a central controller may receive a startup command, and the central controller may then cause one or more lamps to startup in an order which limits the current draw on the system. For example, the central controller may start the lamps in series, in parallel, or in any combination thereof. According to other embodiments, a decentralized startup controller (e.g., a startup circuit, control startup circuit, etc., described below) may be coupled to and control the startup of each lamp such that the overall power draw of the plurality of lamps is maintained within acceptable limits during startup. 
     Referring to  FIG. 7 , a lamp  700  is shown according to an exemplary embodiment. Further referring to  FIG. 8 , a plurality of lamps  700 , shown as first through third lamps  700   a - c , are coupled to an electrical system  776 . For example, the contacts  714  of the lamp  700  may couple to the power lines  776   a  and  776   b  of the electrical system  776 . 
     The lamp  700  is shown to include a startup circuit  760  (e.g., a controller) coupled to the lamp  700 . The startup circuit  760  may include any number of mechanical or electrical circuitry components or modules for controlling the startup of the lamp  700 . For example, the startup circuit  760  may include a switch, a capacitor, an inductor, a resistor, or other solid state circuitry components. According to another embodiment, the startup circuit  760  may include a processor as described above. The processor may be or include one or more microprocessors, an application specific integrated circuit (ASIC), a circuit containing one or more processing components, a group of distributed processing components, circuitry for supporting a microprocessor, or other hardware configured for processing. According to an exemplary embodiment, the processor is configured to execute computer code stored in a memory to complete and facilitate the activities described herein. The memory can be any volatile or non-volatile memory device capable of storing data or computer code relating to the activities described herein. For example, the memory may include modules that are computer code modules (e.g., executable code, object code, source code, script code, machine code, etc.) configured for execution by the processor. When the code modules are executed by the processor, the control circuit is configured to complete the activities described herein. 
     According to one embodiment, the startup circuit  760  is configured start the lamp  700  at a time relative to a plurality of other lamps such that the current draw on an electrical system providing power to the lamp is maintained below a first power level. 
     According to another embodiment, the startup circuit  760  includes an input  772  configured to receive a startup signal from another lamp and an output  774  configured to transmit a startup signal. The startup circuit  760  is configured to delay starting the lamp  700  for a second period of time in response to the input  772  receiving a startup signal within a first period of time after the startup circuit  760  receives a startup command. The startup circuit  760  is further configured to start the lamp  700  and cause the output  774  to transmit (e.g., broadcast, output, provide, cause to be transmitted, etc.) a startup signal in response to the input  772  not receiving a startup signal within the first period of time after the startup circuit receives the startup command. The first and second periods of time may be random amounts of time and may be limited to less than one second. According to an exemplary embodiment, the startup signal may be passed over a power line  776   a,    776   b.  According to other embodiments, the startup signal may be passed over a dedicated line, over a wired network connection, over another line, or wirelessly. 
     In operation, the system of this embodiment may act as a collision avoidance system. For example, the plurality of lamps  700  may receive the startup command at substantially the same time. Each of the lamps  700  then waits its first period of time. The lamp  700  with the first expiring period of time, for example lamp  700   a,  having not received a startup signal begins to start and broadcasts a startup signal to the other lamps  700  (e.g., lamps  700   b,    700   c ). These other lamps  700   b,    700   c  each wait its second period of time. The lamp having the first expiring second period of time, for example lamp  700   c,  having not received a startup signal during the second period of time begins to start and broadcasts a startup signal to the other lamps  700  (e.g., lamps  700   a,    700   b ). Lamp  700   b  then waits a third period of time, and having not received a startup signal during the third period of time begins to startup and transmits a startup signal. The concepts of this system may be expanded to any number of lamps. 
     Referring to  FIG. 9 , a lamp  900  is shown according to an exemplary embodiment. The lamp  900  may be a mercury-free low-pressure lamp having a bulb  901  having one or more phosphors  904  configured to convert photons to visible wavelengths, having an envelope  902  filled with a gas at low pressure, and having at least one emissive material including at least one of an alkali metal and an alkaline earth metal. The envelope  902  may be filled with one or more inert gases  908 . The lamp  900  further includes a control startup circuit  960  configured, in response to a startup command, to cause the vaporization of the emissive material into the envelope and to cause the excitation of the emissive material with an electron such that the emissive material in combination with the inert gases generate visible or ultraviolet photons. The control startup circuit  960  may be coupled to or incorporated into the lamp  900 , for example, in the end plug  916 , as shown; or, as shown in  FIG. 11 , the control startup circuit  1160  may be coupled to or incorporated into a fixture  1106  configured to support the bulb  1101  of the lamp  1100 . 
     The control startup circuit  960  may include any number of mechanical or electrical circuitry components or modules for controlling the control startup of the lamp  900 . For example, the control startup circuit  960  may include a switch, a capacitor, an inductor, a resistor, or other solid state circuitry components. According to another embodiment, the startup circuit  960  may include a processing electronics  961 . 
     Referring now to  FIG. 10 , a detailed block diagram of processing electronics  1000  configured to execute the systems and methods of the present disclosure is shown, according to an exemplary embodiment. The processing electronics  1000 , or components and modules thereof, may be included in the lamps of  FIGS. 3-9, 11, and 23-26 , for example, as part of control circuit  360 , startup circuit  760 , control startup circuit  960 , control startup circuit  1160 , control circuit  2360 , control circuit  2460 , control circuit  2560 , or control circuit  2660 . Processing electronics  1000  includes a memory  1004  and processor  1002 . Processor  1002  may be or include one or more microprocessors, an application specific integrated circuit (ASIC), one or more field programmable gate arrays (FPGAs), a circuit containing one or more processing components, a group of distributed processing components, circuitry for supporting a microprocessor, or other hardware configured for processing. According to an exemplary embodiment, processor  1002  is configured to execute computer code stored in memory  1004  to complete and facilitate the activities described herein. Memory  1004  can be any non-transient, volatile or non-volatile memory device capable of storing data or computer code relating to the activities described herein. For example, memory  1004  is shown to include modules  1010 - 1016  which are computer code modules (e.g., executable code, object code, source code, script code, machine code, etc.) configured for execution by processor  1002 . When executed by processor  1002 , processing electronics  1000  is configured to complete the activities described herein. Processing electronics  1000  includes hardware circuitry for supporting the execution of the computer code of modules  1010 - 1016 . For example, processing electronics  1000  includes hardware interfaces (e.g., output  1020 ) for communicating control signals (e.g., analog, digital) from processing electronics  1000  to control startup circuit  960 . The output  1020  may be, include, or communicate with the output  974  of the circuit  960 . Processing electronics  1000  may also include an input  1030  for receiving, for example, a startup command from input  972 , feedback signals from the heater  930  or the cooler  940 , or for receiving data or signals from other, sensors, systems, or devices. The input  1030  may be, include, or communicate with the input  972  of the circuit  960 . 
     The memory  1004  is shown to include a memory buffer  1006 . The memory buffer  1006  is configured to receive data via an input  1030 . The data may include data from a temperature sensor or temperature controller, data from an optical sensor, data from an input relating to a startup signal or startup command, data that may be used to determine whether a heater or cooler should or should not be activated, or other data that may be used to determine whether a heater or cooler should or should not be deactivated. 
     The memory  1004  further includes configuration data  1008 . The configuration data  1008  includes data relating to the processing electronics  1000  or to various controllers, thermal sensors, or optical sensors. For example, the configuration data  1008  may include information relating to a retrieval process of data from a sensor (e.g., transfer functions for thermocouples, photocells, etc.). The configuration data  1008  may also include data regarding the number, size and orientation of reservoirs, heaters, and coolers. For example, a high lumen output lamp may have more emissive material and more reservoirs. 
     The memory  1004  is shown to include a communication module  1010 . The communication module  1010  is configured to provide communication capability with other components of the circuit  960  via the output  1020 . For example, the communication module  1010  may be configured to activate or deactivate the heater  930  or the cooler  940  in response to a determination by the heater module  1012  or the cooler module  1014 , respectively. The communication module  1010  may be configured to receive a startup command and to cause a startup signal to be transmitted. 
     The memory  1004  is shown to include a heater module  1012  configured to control the heater  930 . The heater module  1012  may be configured to cause the heater  930  to heat or cease heating, for example, in response to a startup command, a signal from a sensor  962 , or a command from the startup module  1016 . The heater module  1012  may be configured to control the operation of various heaters  930  such that a plurality of reservoirs  950  and/or the emissive material  920  therein may be heated sequentially, simultaneously, or any combination thereof. 
     The memory  1004  is shown to include a cooler module  1014  configured to control the cooler  940 . The cooler module  1014  may be configured to cause the cooler  940  to cool or cease cooling, for example, in response to a startup command, a shutdown command, a signal from a sensor  962 , or a command from the startup module  1016 . For example, in the case where the lamp  900  is switched off and then soon after switched back on, the cooler module  1014  may cause the cooler  940  to cool in response to the shutdown command, but may then cause the cooler  940  to cease cooling in response to the startup command. The cooler module  1014  may further include logic for charging and discharging the energy storage device  968 , for example, via a charger  976  coupled to the contacts  914 , a photovoltaic cell (e.g., sensor  962 ), or a thermoelectric generator. 
     The memory  1004  is shown to include a startup module  1016 . The startup module  1016  is configured to cause the lamp  900  to startup in response to a startup command. For example, the startup module  1016  may control the ballast, for example, if the ballast is an electronic ballast. The startup module  1016  may include a timer and logic for generating a random value for use with a decentralized startup control system. The startup module  1016  may communicate with the communication module  1010  to receive a startup command and to cause transmission of a startup signal. For example, the startup module  1016  may include logic for carrying out the processes of startup circuit  760  as described above with respect to  FIGS. 7 and 8 . According to other embodiments, the startup module  1016  may include logic for controlling an injector and carrying out the processes as described in relation to  FIGS. 18-20 . 
     Returning to  FIG. 9 , the control startup circuit  960  may include or couple to the heater  930  configured to raise the temperature of a first portion (e.g., the reservoir  950 ) of the lamp  900  and/or the emissive material  920  therein such that the vapor pressure of the emissive material  920  is increased such that the emissive material  920  begins to vaporize. The control startup circuit  960  may be configured to switch off the heater  930  in response to an input, for example, the passage of time, a temperature of the lamp  900 , an optical output of the lamp  900 , or an electrical state of the lamp  900 . The control startup circuit  960  may include or couple to the cooler  940  configured to reduce the temperature of at least a second portion (e.g., the reservoir  950 ) of the lamp  900  such that the emissive material  920  preferentially condenses at the second portion of the lamp  900 . The control startup circuit  960  may be configured to switch off the cooler  940  in response to an input, for example, a profile of time, a temperature of the lamp  900 , an optical output of the lamp  900 , an electrical property of the lamp  900 , a startup command, etc. The control startup circuit  960  may be configured to provide power to the heater  930  and the cooler  940 . For example the control startup circuit  960  may include or pass on power from an energy storage device  968  or may pass on power from a power supply coupled to the contacts  914 . 
     Referring generally to  FIGS. 12-17 , various processes for operating a mercury-free low-pressure arc discharge lamp are shown. The processes of  FIGS. 12-17  may be implemented by the various systems described in  FIGS. 1-11 . 
     Referring to  FIG. 12 , a flowchart of a process  1200  for operating a low-pressure arc discharge lamp is shown, according to an exemplary embodiment. The process  1200  includes the steps of providing a bulb having one or more phosphors configured to convert photons to visible wavelengths, an envelope filled with one or more gases at low pressure, and an emissive material including at least one of an alkali metal and an alkaline earth metal (step  1202 ), vaporizing at least a portion of the emissive material into the envelope to form an emitter (step  1204 ), exciting the emitter with an electron such that the emitter in combination with the gases generate visible or ultraviolet photons (step  1206 ), and converting at least a portion of the photons to other visible wavelengths (step  1208 ). 
     Referring to  FIG. 13 , a flowchart of a process  1300  for operating a low-pressure arc discharge lamp is shown, according to an exemplary embodiment. The process  1300  includes the steps of providing a bulb having one or more phosphors configured to convert photons to visible wavelengths, an envelope filled with one or more inert gases at low pressure, and an emissive material including at least one of an alkali metal and an alkaline earth metal (step  1302 ), and heating the emissive material such that the vapor pressure of an emissive material is increased such that the emissive material begins to vaporize (step  1304 ). The process  1300  further includes the steps of exciting the emissive material with an electron such that the emissive material in combination with the inert gases generate visible or ultraviolet photons (step  1306 ), converting at least a portion of the photons to other visible wavelengths (step  1308 ), ceasing heating in response to an input (step  1310 ), and cooling a portion of the lamp such that the emissive material preferentially condenses at the second portion of the lamp (step  1312 ). 
     Referring to  FIG. 14  a flowchart of a process  1400  for operating a low-pressure arc discharge lamp is shown, according to an exemplary embodiment. The process  1400  includes the steps of providing a bulb having one or more phosphors configured to convert photons to visible wavelengths, an envelope filled with one or more inert gases at low pressure, and an emissive material including at least one of an alkali metal and an alkaline earth metal (step  1402 ), vaporizing at least a portion of the emissive material into the envelope (step  1404 ), exciting the emissive material with an electron such that the emissive material in combination with the inert gases generate visible or ultraviolet photons (step  1406 ), and converting at least a portion of the photons to other visible wavelengths (step  1408 ). The process  1400  further includes the step of charging an energy storage device while the lamp is switched on, the energy storage device configured to provide power to a cooler, the cooler configured to cool a cold spot (step  1410 ). The process  1400  further includes the step of cooling the cold spot such that the emissive material preferentially condenses at cold spot of the lamp (step  1412 ). 
     Referring to  FIG. 15  a flowchart of a process  1500  for operating a low-pressure arc discharge lamp is shown, according to an exemplary embodiment. The process  1500  includes the steps of providing a bulb having one or more phosphors configured to convert photons to visible wavelengths, an envelope filled with one or more inert gases at low pressure, and an emissive material including at least one of an alkali metal and an alkaline earth metal (step  1502 ), and starting the lamp at a time relative to a plurality of other lamps such that the current draw on an electrical system providing power to the lamp is maintained below a first power level (step  1504 ). The process  1500  further includes the steps of vaporizing at least a portion of the emissive material into the envelope (step  1506 ), exciting the emissive material with an electron such that the emissive material in combination with the inert gases generate visible or ultraviolet photons (step  1508 ), and converting at least a portion of the photons to other visible wavelengths (step  1510 ). 
     Referring to  FIG. 16  a flowchart of a process  1600  for operating a low-pressure arc discharge lamp is shown, according to an exemplary embodiment. The process  1600  includes the steps of providing a bulb having one or more phosphors configured to convert photons to visible wavelengths, an envelope filled with one or more inert gases at low pressure, and an emissive material including at least one of an alkali metal and an alkaline earth metal (step  1602 ), receiving a startup command (step  1604 ), and waiting a period of time after receiving the startup command (step  1606 ). The process  1600  then determines if a startup signal is received during the period of time (step  1608 ). If a startup signal is received during the period of time, then the process  1600  waits another period of time before returning to the determining step  1608  (step  1610 ). If a startup signal is not received during the period of time, then the process  1600  proceeds to starting the lamp (step  1614 ). The process  1600  further includes the steps of vaporizing at least a portion of the emissive material into the envelope (step  1616 ), exciting the emissive material with an electron such that the emissive material in combination with the inert gases generate visible or ultraviolet photons (step  1618 ), and converting at least a portion of the photons to other visible wavelengths (step  1620 ). 
     Referring to  FIG. 17  a flowchart of a process  1700  for operating a low-pressure arc discharge lamp is shown, according to an exemplary embodiment. The process  1700  includes the steps of providing a bulb having one or more phosphors configured to convert photons to visible wavelengths, an envelope filled with one or more inert gases at low pressure, and an emissive material including at least one of an alkali metal and an alkaline earth metal (step  1702 ), receiving a startup command (step  1704 ). The process  1700  then determines if the present line-voltage of the electrical is less than approximately 95 percent of a long-term-average voltage of the electrical system (step  1706 ). If the determination is yes, then the process limits the power drawn by the lamp to a first value (step  1708 ) and proceeds to vaporizing at least a portion of the emissive material into the envelope (step  1710 ). If the determination is no, the process  1700  proceeds directly to the vaporizing step  1710  without limiting the power drawn. The process  1700  further includes the steps of exciting the emissive material with an electron such that the emissive material in combination with the inert gases generate visible or ultraviolet photons (step  1712 ), and converting at least a portion of the photons to other visible wavelengths (step  1714 ). 
     Referring to  FIGS. 18-20 , lamps  1800 ,  1900 , and  2000  are shown, according to exemplary embodiments. As described above, the lamps  1800 ,  1900 ,  2000  are low-pressure lamps (e.g., arc discharge lamps) using a non-mercury emissive material  1820 ,  1920 ,  2020 . Due the relatively low vapor pressure of the non-mercury emissive material, the lamps  1800 ,  1900 ,  2000  include an injector  1880 ,  1980 ,  2080  (e.g., sprayer, atomizer, jet, etc.) configured to spray (e.g., inject, discharge, etc.) at least some of the emissive material  1820 ,  1920 ,  2020  into the envelope  1802 ,  1902 ,  2002 . According to exemplary embodiments, a controller (e.g., startup circuit  760 , control startup circuit  960 , startup module  1016 , etc.) may be configured to control actuation of the injector  1880 ,  1980 ,  2080 . 
     Referring to  FIG. 18 , the injector  1880  is shown to include a nozzle  1881  and an injection chamber  1882 . A capillary  1883  is configured to move (e.g., draw, transport, etc.) the emissive material from the reservoir  1850  to the injection chamber  1882 . A cooler  1840  may be coupled to the reservoir  1850  to induce condensation the emissive material  1820  at the reservoir  1850  after the prior shutdown. A heater  1830  may be coupled to the reservoir  1850  in order heat the emissive material  1820  prior to injection. Heating the emissive material  1820  raises the vapor pressure of the emissive material  1820 , facilitating a finer spray and increases the fluidity of the emissive material  1820 , facilitating flow of the emissive material  1820  from the reservoir  1850  to the injection chamber  1882 . Depending on the materials used for the emissive material  1820 , the heater  1830  may melt a solidified emissive material  1820  in the reservoir  1850  so that the emissive material  1820  can be more easily sprayed by the injector  1880 . 
     According to the embodiment shown, the injector  1880  uses a piezoelectric element  1884  to create a pressure wave in the injection chamber  1882 . The pressure wave pushes at least some of the emissive material  1820  into the envelope  1802 . The emissive material  1820  that is sprayed into the envelope  1802  may be sufficiently atomized that the emissive material  1820  can be excited by electrons and ions in the envelope  1802 . According to another embodiment, the emissive material  1820  that is sprayed into the envelope  1802  may be sufficiently fine that an ionized gas (e.g., plasma) in the envelope  1802  may quickly and easily vaporize the emissive material  1820  such that the emissive material  1820  can be excited in order to produces photons. 
     Referring to  FIG. 19 , the emissive material  1920  flows into an injection chamber  1982 . A heater  1986 , which may be the same or separate from the heater  1930 , heats the emissive material  1920  in the injection chamber  1982  causing the emissive material  1920  to expand. At least some of the emissive material  1920  is pushed out of the injection chamber  1982  through the nozzle  1981 . According to one embodiment, the emissive material  1920  expelled through the nozzle  1981  forms a bubble  1922 . Continued heating of the emissive material  1920  by the heater  1986  causes the bubble  1922  to pop, releasing particles of the emissive material  1920  into the envelope. The particles of the emissive material  1920  may be sufficiently fine to release photons in response to electronic excitation or may be sufficiently fine to be quickly and easily vaporized by the ionized gas in the envelope  1902 . 
     Referring to  FIG. 20 , the emissive material  2020  may be conductive as a liquid. Accordingly, an electromagnet  2088  may be used to generate a force to act upon the emissive material  2020 . The electromagnetic force draws the emissive material  2020  from the reservoir  2050  and forces the emissive material  2020  into the envelope  2002  through the nozzle  2081 . The nozzle  2081  may be configured to cause the discharged emissive material  2020  to form a mist of emissive material  2020  particles. The particles of the emissive material  2020  may be sufficiently fine to release photons in response to electronic excitation or may be sufficiently fine to be quickly and easily vaporized by the ionized gas in the envelope  2002 . 
     Referring generally to  FIGS. 21-22 , various processes for operating a mercury-free low-pressure arc discharge lamp are shown. The processes of  FIGS. 21-22  may be implemented by the various systems described in  FIGS. 18-20 . 
     Referring to  FIG. 21 , a flowchart of a process  2100  for starting a low-pressure arc discharge lamp is shown, according to an exemplary embodiment. The process  2100  includes the steps of providing a bulb having one or more phosphors configured to convert photons to visible wavelengths and an envelope filled with one or more gases (e.g., inert gases) (step  2102 ), spraying at least a portion of the emissive material into the envelope, the emissive material comprising at least one of an alkali metal and an alkaline earth metal (step  2104 ), and exciting the emissive material with an electron such that the at least one emissive material in combination with the one or more gases generate visible or ultraviolet photons (step  2106 ). 
     Referring to  FIG. 22 , a flowchart of a process  2200  for starting a low-pressure arc discharge lamp is shown, according to another embodiment. The process  2200  includes the steps of providing a bulb having one or more phosphors configured to convert photons to visible wavelengths and an envelope filled with one or more inert gases (step  2202 ), and cooling a portion of the lamp such that an emissive material preferentially condenses at the cooled portion of the lamp, the emissive material comprising at least one of an alkali metal and an alkaline earth metal (step  2204 ). The process  2200  further includes the steps of melting the emissive material such that the emissive material may be sprayed (step  2206 ), drawing the emissive material into an injection chamber using capillary action (step  2208 ), spraying at least a portion of the emissive material into the envelope, (step  2210 ), and exciting the emissive material with an electron such that the at least one emissive material in combination with the one or more inert gases generate visible or ultraviolet photons (step  2212 ). According to an exemplary embodiment, a period of time may lapse between the cooling step  2204  and the melting step  2006 . For example, the cooling step  2204  may occur during or after prior operation of the lamp, and a period of seconds, minutes, hours, days, weeks, months, or years may pass between the cooling step  2206  and the melting step  2206 , which may be triggered in response to a startup command. 
     The construction and arrangement of the elements of the systems and methods as shown in the exemplary embodiments are illustrative only. Although only a few embodiments of the present disclosure have been described in detail, those skilled in the art who review this disclosure will readily appreciate that many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter recited. For example, elements shown as integrally formed may be constructed of multiple parts or elements. It should be noted that the elements and assemblies described herein may be constructed from any of a wide variety of materials that provide sufficient strength or durability, in any of a wide variety of colors, textures, and combinations. Additionally, in the subject description, the word “exemplary” is used to mean serving as an example, instance, or illustration. Any embodiment or design described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments or designs. Rather, use of the word exemplary is intended to present concepts in a concrete manner. Accordingly, all such modifications are intended to be included within the scope of the present inventions. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. Other substitutions, modifications, changes, and omissions may be made in the design, operating conditions, and arrangement of the preferred and other exemplary embodiments without departing from scope of the present disclosure or from the scope of the appended claims. 
     The present disclosure contemplates methods, systems and program products on any machine-readable media for accomplishing various operations. The embodiments of the present disclosure may be implemented using existing computer processors, or by a special purpose computer processor for an appropriate system, incorporated for this or another purpose, or by a hardwired system. Embodiments within the scope of the present disclosure include program products comprising machine-readable media for carrying or having machine-executable instructions or data structures stored thereon. Such machine-readable media can be any available media that can be accessed by a general purpose or special purpose computer or other machine with a processor. By way of example, such machine-readable media can comprise RAM, ROM, EPROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to carry or store desired program code in the form of machine-executable instructions or data structures and which can be accessed by a general purpose or special purpose computer or other machine with a processor. When information is transferred or provided over a network or another communications connection (either hardwired, wireless, or a combination of hardwired or wireless) to a machine, the machine properly views the connection as a machine-readable medium. Thus, any such connection is properly termed a machine-readable medium. Combinations of the above are also included within the scope of machine-readable media. Machine-executable instructions include, for example, instructions and data which cause a general purpose computer, special purpose computer, or special purpose processing machines to perform a certain function or group of functions. 
     Although the figures may show a specific order of method steps, the order of the steps may differ from what is depicted. Also two or more steps may be performed concurrently or with partial concurrence. Such variation will depend on the software and hardware systems chosen and on designer choice. All such variations are within the scope of the disclosure. Likewise, software implementations could be accomplished with standard programming techniques with rule based logic and other logic to accomplish the various connection steps, processing steps, comparison steps and decision step.