23-09-2014, 11:09 AM
Electroless lamp
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1. INTRODUCTION
An electrodeless lamp is a light source in which the power required to generate light is transferred from the outside of the lamp envelope by means of (electro)magnetic fields, in contrast with a typical electrical lamp that uses electrical connections through the lamp envelope to transfer power. There are three advantages of eliminating electrodes:
• Extended lamp life, because the electrodes are usually the limiting factor in lamp life.
• The ability to use high efficiency light-generating substances that would react with metal electrodes in normal lamps.
• Improved collection efficiency because the source can be made very small without shortening life - a problem in electroded lamps
Two systems are described below—one, plasma lamps, based on the use of radio waves energizing a bulb filled with sulfur or metal halides, the other, fluorescent induction lamps, based upon conventional fluorescent lamp phosphors.
. PLASMA LAMPS
Plasma lamps are a family of light sources that generate light by exciting a plasma inside a closed transparent burner or bulb using radio frequency (RF) power. Typically, such lamps use a noble gas or a mixture of these gases and additional materials such as metal halides, sodium, mercury or sulfur. A waveguide is used to constrain and focus the electrical field into the plasma. In operation the gas is ionized and free electrons, accelerated by the electrical field collide with gas and metal atoms. Some electrons circling around the gas and metal atoms are excited by these collisions, bringing them to a higher energy state. When the electron falls back to its original state, it emits a photon, resulting in visible light or ultraviolet radiation depending on the fill materials.
The first plasma lamp was an ultraviolet curing lamp with a bulb filled with argon and mercury vapor developed by Fusion UV. That lamp led Fusion Systems to the development of the sulfur lamp, a bulb filled with argon and sulfur which is bombarded with microwaves through a hollow waveguide.
In the past, the reliability of the technology was limited by the magnetron used to generate the microwaves. Solid state RF generation can be used and gives long life. However, using solid state chips to generate RF is approximately fifty times more expensive currently than using a magnetron and so only appropriate for high value lighting niches. It has recently been shown by Dipolar [1] of Sweden to be possible to greatly extend the life of magnetrons to over 40,000 hours [7] making low cost plasma lamps possible. Plasma lamps are currently produced by Ceravision and Luxim and in development by Topanga Technologies.
Ceravision has introduced a combined lamp and luminaire under the trade name Alvara for use in high bay and street lighting applications. It uses an optically clear quartz waveguide with an integral burner allowing all the light from the plasma to be collected. The small source also allows the luminaire to
utilize more than 90% of the available light compared with 55% for typical HID fittings. Ceravision claims the highest Luminaire Efficacy Rating (LER) [8] of any light fitting on the market and to have created the first High Efficiency Plasma (HEP) lamp. Ceravision uses a magnetron to generate the required RF power and claim a life of 20,000 hours.
Luxim's LIFI, or light fidelity lamp, claims 120 lumens per RF watt (ie before taking into account electrical losses).[9] The lamp has been used in Robe lighting's ROBIN 300 Plasma Spot moving headlight.[10] It was also used in a line of, now discontinued, Panasonic rear projection TV's.
ADVANTAGES
• Long lifespan due to the lack of electrodes - between 65,000 and 100,000 hours depending on the lamp model;
• Very high energy conversion efficiency of between 62 and 90 Lumens/Watt [higher wattage lamps are more energy efficient];
• High power factor due to the low loss of the high frequency electronic ballasts which are typically between 95% and 98% efficient;
• Minimal Lumen depreciation (declining light output with age) compared to other lamp types as filament evaporation and depletion is absent;
• “Instant-on” and hot re-strike, unlike most conventional lamps used in commercial/industrial lighting applications (such as Mercury-vapor lamp, Sodium-vapor lamp and Metal halide lamp);
• Environmentally friendly as induction lamps use less energy, and use less mercury per hour of operation than conventional lighting due to their long lifespan. The mercury is in a solid form and can be easily recovered if the lamp is broken, or for recycling at end-of-life.
These benefits offer a considerable cost savings of between 35% and 55% in energy and maintenance costs for induction lamps compared to other types of commercial and industrial lamps which they replace.