Plasma lamps are a type ofelectrodeless gas-discharge lamp energized byradio frequency (RF) power. They are distinct from thenovelty plasma lamps that were popular in the 1980s.
The internal-electrodeless lamp was invented byNikola Tesla after his experimentation with high-frequencycurrents in evacuated glasstubes for the purposes of lighting and the study ofhigh voltage phenomena. The first practical plasma lamps were thesulfur lamps manufactured by Fusion Lighting. This lamp suffered several practical problems and did not prosper commercially. Plasma lamps with an internal phosphor coating are calledexternal electrode fluorescent lamps (EEFL); these external electrodes or terminal conductors provide the radio frequency electric field.
Modern plasma lamps are a family of light sources that generate light by excitingplasma inside a closed transparent burner or bulb usingradio frequency (RF) power. Typically, such lamps use anoble gas or a mixture of these gases and additional materials such as metalhalides,sodium,mercury orsulfur. In modern plasma lamps, awaveguide is used to constrain and focus theelectrical field into the plasma. In operation, the gas is ionized, and freeelectrons, accelerated by theelectrical field, collide with gas and metal atoms. Some atomic electrons circling around the gas and metal atoms areexcited by these collisions, bringing them to a higher energy state. When the electron falls back to its original state, it emits aphoton, resulting in visible light orultraviolet radiation, depending on the fill materials.
The first commercial plasma lamp was an ultravioletcuring lamp with a bulb filled with argon and mercury vapor developed byFusion UV. That lamp led Fusion Lighting to the development of thesulfur lamp, a bulb filled with argon and sulfur that is bombarded with microwaves through a hollowwaveguide. The bulb had to be spun rapidly to prevent the sulfur from burning through. Fusion Lighting did not prosper commercially, but other manufacturers continue to pursuesulfur lamps. Sulfur lamps, though relatively efficient, have had several problems, chiefly:
In the past, the life of the plasma lamps was limited by themagnetron used to generate the microwaves. Solid-state RF chips can be used and give long lives. However, using solid-state chips to generate RF is currently an order of magnitude more expensive than using amagnetron and so only appropriate for high-value lighting niches.
The use of a high-dielectric waveguide allowed the sustaining of plasmas at much lower powers—down to 100 W in some instances. It also allowed the use of conventionalgas-discharge lamp fill materials which removed the need to spin the bulb. The only issue with the ceramic waveguide was that much of the light generated by the plasma was trapped inside the opaque ceramic waveguide.
High-efficiency plasma lighting is the class of plasma lamps that have system efficiencies of 90lumens per watt or more. Lamps in this class are potentially the most energy-efficient light source for outdoor, commercial, and industrial lighting. This is due not only to their high system efficiency but also to the small light source they present enabling very high luminaire efficiency.
Luminaire Efficacy Rating (LER) is the single figure of merit theNational Electrical Manufacturers Association has defined to help address problems with lighting manufacturers' efficiency claims[1] and is designed to allow robust comparison between lighting types. It is given by the product of luminaire efficiency (EFF) times total rated lamp output in lumens (TLL) times ballast factor (BF), divided by the input power in watts (IP):
The "system efficiency" for a high-efficiency plasma lamp is given by the last three variables, that is, it excludes the luminaire efficiency. Though plasma lamps do not have a ballast, they have an RF power supply that fulfills the equivalent function. In electrodeless lamps, the inclusion of the electrical losses, or "ballast factor", in lumens per watt claimed can be particularly significant as the conversion of electrical power to radio frequency (RF) power can be a highly inefficient process.
Many modern plasma lamps have very small light sources—far smaller than HID bulbs or fluorescent tubes—leading to much higher luminaire efficiencies also.High-intensity discharge lamps have typical luminaire efficiencies of 55%, andfluorescent lamps of 70%. Plasma lamps typically have luminaire efficiencies exceeding 90%.
Plasma lamps have been used in high bay andstreet lighting applications, as well as instage lighting. They were briefly used in someprojection televisions.[2][3][4]
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